Method and apparatus for soldering electronic components to circuit boards

Abstract

The present invention relates to a method for soldering an electronic component (1) having a pin (4) inserted into a through hole (3) to a circuit board (2) having the through hole (3). The method is characterized in that a liquefied solder ball (5) is applied, particularly sprayed, onto the circuit board (2), such that a portion of the liquefied solder ball (5) flows in and fills the annular gap between the pin (4) and the through hole (3).

Description

Technical Field

[0001] This disclosure relates to a method and apparatus for soldering electronic components having pins inserted into through-holes to a circuit board having through-holes. This disclosure also relates to a computer program product and a computer-readable medium. Background Technology

[0002] Surface mount technology (SMT) allows electronic components to be directly mounted onto the surface of a circuit board (such as a printed circuit board (PCB)). Electronic components mounted in this way are called surface mount devices (SMDs). SMT has largely replaced through-hole technology (THT), in which the leads of a through-hole device (THD) are inserted into through-holes in the circuit board, because SMT allows for increased manufacturing automation, which reduces costs and improves soldering quality.

[0003] However, THT is still required for electronic components that are not suitable for SMT. This is when high mechanical strength or heat sinks are required. Exemplary electronic components are large transformers, power semiconductors (such as power transistors, lasers, and light-emitting diodes (LEDs)) with heat sinks, or connectors. To ensure a sufficiently strong connection between the THT and the circuit board, the annular gap formed between the via and the pin inserted into the via needs to be filled with solder at least 70%. In the following text, a fill degree of more than 70% of the annular gap volume is also referred to as high fill degree.

[0004] Therefore, circuit boards are typically packaged using both SMT and THT methods. In the following text, this type of circuit board is referred to as a hybrid package circuit board.

[0005] To produce hybrid packaged circuit boards, WO 03 / 079 743 A2 teaches the use of a so-called back-side reflow method to solder a thermally critical device (THD) with a thermally critical housing to a circuit board. In this method, the hybrid packaged circuit board is specifically produced by pre-assembling a first side of the circuit board with the SMD and THD, rotating the circuit board so that the first side of the circuit board is below a second side of the circuit board, and pre-assembling only the second side of the circuit board with the SMD. The SMD is pre-assembled onto the circuit board by placing the contacts of the SMD on corresponding locations on the circuit board where solder paste is applied. The SMD can be secured to the circuit board with adhesive. The THD is pre-assembled by inserting the leads of the THD into through-holes on the first side, such that the leads protrude from the second side in the contact area where solder paste is applied. To prevent the THD from detaching when the circuit board is flipped, the THD can be secured to the circuit board with adhesive or a soft-locking technique, wherein the through-hole includes a collar portion to hold the THD leads. The circuit board is then inserted into a reflow oven and heated such that the first side of the circuit board with the THD mounted thereon is at least partially shielded from the heat or energy affecting soldering.

[0006] A further development of the above method is disclosed in DE 10 2008 035 405 A1. In this method, the circuit board has SMDs pre-assembled on two sides and at least one THD pre-assembled on the first side. Instead of adhesives or soft-locking devices, at least one THD is secured to the first side of the circuit board by selectively soldering at least one pin of the THD to the circuit board before the circuit board is flipped over to encapsulate the second side with the SMDs. The circuit board is then inserted into a reflow oven to solder the SMDs and THDs to the circuit board.

[0007] Another method for manufacturing a hybrid packaged circuit board is disclosed in DE 10 2005 043 279 A1. In this method, the circuit board is only packaged with SMDs and placed in a reflow oven for soldering the SMDs to the circuit board. Then, at least one THD is selectively soldered to the circuit board.

[0008] To selectively solder the pins of the THD to the circuit board, solder cans are driven in three orthogonal directions—the X, Y, and Z directions in a Cartesian coordinate system—to contact the corresponding pins protruding from the vias. Furthermore, flux needs to be applied to the pins to prevent oxidation and achieve proper soldering. However, compared to soldering methods using a reflow oven, the movement in the Z direction requires a longer time to solder the THD to the circuit board, allowing the solder cans to advance to or from the pins respectively. Therefore, EP 3 153 270 A1 proposes using at least two solder cans, each driven individually in one of the three orthogonal directions, to improve soldering speed. However, a drawback remains: when selectively soldering the pins of the THD to the circuit board using solder cans, the amount of solder applied to the pins cannot be precisely controlled. Summary of the Invention

[0009] Therefore, the purpose of this disclosure is to overcome the shortcomings of the prior art and to provide an advanced method and apparatus for soldering electronic components with pins having through-holes to a circuit board having through-holes. Furthermore, the method and apparatus according to this disclosure can also be used in the manufacture of hybrid packaged circuit boards.

[0010] This objective is achieved by the method and apparatus according to the invention. This objective is also achieved by the computer program product and computer-readable medium according to the invention.

[0011] According to the method of this disclosure, this objective is achieved by applying liquefied solder balls, particularly by spraying them onto a circuit board comprising through-holes into which leads of electronic components are inserted, such that a portion of the liquefied solder balls flows in and fills the annular gap between the leads and the through-holes. Therefore, this method can be used for thermally critical electronic components. Furthermore, it eliminates the need for the solder can to advance to or exit from the leads, thereby reducing the time required to solder electronic components with leads inserted into the through-holes to a circuit board with through-holes. Additionally, by applying liquefied solder balls, the amount of solder applied to the through-holes can be appropriately controlled. It should be noted that the liquefied solder balls partially fill at least 70% of the volume of the annular gap to ensure proper engagement between the leads and the through-holes. It should also be mentioned that the volume of the solder balls is preferably larger than the volume of the annular gap, and solder is also present outside the through-holes after the liquefied solder flows into the annular gap. After the liquefied solder fills the annular gap, it solidifies and forms a permanent conductive joint between the leads and the through-holes. As described above, the liquefied solder balls are specifically sprayed onto the circuit board. A method and apparatus for applying, in particular spraying, liquefied welding balls are disclosed in WO 02 / 28 588 A1. The contents of that document are incorporated herein by reference.

[0012] According to one aspect of this disclosure, the ratio of the diameter to the depth of the via can be in the range of 0.5 to 3. Preferably, this ratio can be 1. Furthermore, the diameter of the via can be 1.5 to 3 times the pin diameter. Preferably, the diameter of the via can be 2 times the pin diameter. Furthermore, the height of the pin above the circuit board surface can be 0 or equal to or less than 0.5 times the via diameter. Furthermore, the diameter of the solder base outside the via can be 1.5 to 2 times the via diameter. Most preferably, the fill factor of the via after soldering can be equal to or greater than 0.7 times the volume of the annular gap formed between the pin and the via. Using the above parameters, the solder joint between the pin and the via provides appropriate mechanical strength and good electrical connection between the contact areas of the pin and the via, which in turn allows connection to leads on the circuit board.

[0013] According to one aspect of this disclosure, after the liquefied solder balls have partially filled the annular gap and after the solder has solidified, the filling degree of the annular gap can be determined by measuring the volume of solidified solder outside the via, based on a predetermined total volume of the liquefied solder balls before application. Preferably, the volume of solidified solder outside the via is measured using three-dimensional image processing. As an example, a 3D scanner, a white light interferometer, or a light field camera can be used to detect the volume of solder outside the via. The volume of solder flowing into the annular gap can be determined by subtracting the measured volume of solidified solder outside the via from the volume of the solder balls known before application. It should be noted that the volume of the pins above the circuit board needs to be subtracted from the volume determined by using three-dimensional image processing to determine the volume of solder outside the via. Furthermore, the volumes and dimensions of the pins and vias are known in advance, such that the volume of the annular gap can also be determined by subtracting the volume of the pins inside the via from the volume of the via. Therefore, the filling degree of the annular gap can be determined by dividing the volume of solder flowing into the annular gap by the volume of the annular gap. Thus, this method enables on-site inspection of the quality of the solder joint. Therefore, the time required for quality inspection of the conductive connections between pins and vias can be reduced. Conversely, fill factor is typically determined using X-ray or cross-sectional inspection. When using reflow soldering or wave soldering, solder cans, X-rays, and cross-sectional inspections are the only methods for determining the fill factor of annular gaps. Therefore, the method according to this disclosure provides a time- and cost-efficient quality inspection, enabling the inspection of more packaged circuit boards, thereby improving overall production quality.

[0014] According to one aspect of this disclosure, liquefied solder balls can be applied to the circuit board from the side opposite to the side of the circuit board where electronic components are arranged. Therefore, liquefied solder balls can be easily applied to the point to be soldered, i.e., the annular gap.

[0015] According to one aspect of this disclosure, liquefied solder balls can be applied downwards onto the circuit board. It should be noted that downwards is defined as the direction of gravity. Therefore, the portion of the liquefied solder balls flowing into the annular gap is supported by gravity, making the annular gap more easily filled with height compared to, for example, the case where liquefied solder balls are applied upwards using a solder can.

[0016] According to one aspect of this disclosure, liquefied solder balls can be applied to a circuit board at an angle. This means that the application direction of the liquefied solder balls is inclined relative to the circuit board (i.e., the surface of the circuit board). Preferably, the angle of inclination relative to the circuit board is in the range of 30° to 60°. More preferably, the angle of inclination relative to the circuit board is substantially 45°. Therefore, the liquefied solder balls can be easily applied to vias, so that the annular gaps are properly filled. Furthermore, the length of the leads can be selected individually, because the length of the leads is not limited by the height of the solder wave or the depth of the solder can. Compared with using a solder can, solder does not need to be applied to the tips of the leads, thereby saving solder material. In particular, when using leads with tips, the liquefied solder balls can be applied at an angle. In this way, laser beam reflection from the tips can be avoided. Furthermore, when using leads with tips, splattering of the liquefied solder balls can be avoided by applying the liquefied solder balls at an angle.

[0017] According to one aspect of this disclosure, the liquefied solder ball can be applied in a direction directed towards the through-hole. Preferably, the application direction is directed towards the point where the pin leaves the through-hole. Therefore, proper application of the liquefied solder ball allows for a high fill degree of the annular gap.

[0018] According to one aspect of this disclosure, energy can be supplied to solid solder balls before liquefied solder balls are applied to generate liquefied solder balls. Therefore, the volume of solder applied to the circuit board (i.e., to the annular gap) is known in advance, and a high fill factor of the annular gap can be achieved by selecting an appropriate volume of solid solder balls relative to the volume of the annular gap.

[0019] According to one aspect of this disclosure, the energy can be a laser beam. Preferably, the laser beam is a near-infrared laser beam adapted to provide power in the NIR range of 200W to 400W. Preferably, the laser beam is supplied for a duration in the range of 20 to 4000 ms. This ensures that the liquefied solder balls are sufficiently liquefied, allowing a portion of the liquefied solder balls to properly flow into and fill the annular gap to achieve proper bonding.

[0020] According to one aspect of this disclosure, a laser beam can be supplied when liquefied solder balls are applied, particularly when they are sprayed onto a circuit board. More specifically, the laser beam is applied to the liquefied solder balls as they fly toward the circuit board. Therefore, liquefaction of the solder balls can be ensured.

[0021] According to one aspect of this disclosure, a laser beam can be continuously or intermittently supplied to solid or liquefied solder balls. Therefore, liquefaction of the solder balls can be ensured.

[0022] According to one aspect of this disclosure, when the liquefied solder ball has reached the circuit board (i.e., reached the surface of the circuit board), a laser beam can be applied to the liquefied solder ball to maintain its liquefaction. The arrival time can be pre-calculated based on the application speed and the distance from which the liquefied solder ball is applied, or it can be determined by image processing or experimentation. Therefore, it can be ensured that a portion of the liquefied solder ball properly flows in and fills the annular gap.

[0023] According to one aspect of this disclosure, the temperature of the solder balls can be measured simultaneously with the supply of energy. Preferably, the energy supply, i.e., the laser beam supply, can be stopped when the temperature of the solid or liquefied solder balls exceeds a predetermined threshold. Preferably, the energy supply, i.e., the laser beam, can be started or restarted when the temperature of the liquefied solder balls falls below a predetermined lower temperature threshold. Therefore, solder burning or solidification can be avoided. This ensures that a portion of the liquefied solder balls properly flows in and fills the annular gap, thereby achieving proper engagement of the leads and vias.

[0024] According to one aspect of this disclosure, the solid solder ball may have a diameter ranging from 0.8 mm to 2.0 mm. Preferably, the diameter of the solder ball is in the range of 0.8 to 1.4 times the diameter of the through-hole. Therefore, a high filling degree of the annular gap can be provided.

[0025] According to an optional aspect of this disclosure, flux may be applied to the via before the application of liquefied solder balls. As mentioned above, flux application is not explicitly required, but it can have a positive effect on the oxidation of the solder, leads, and vias. Therefore, proper bonding of the leads and vias can be achieved.

[0026] According to one aspect of this disclosure, the flux can be activated before the application of liquefied solder balls. Specifically, the flux can be activated by heating it to a temperature between 60°C and 130°C. Preferably, the flux can be activated by supplying energy, more preferably, the supplied energy is a laser beam. Therefore, the bonding between the pins and vias can be positively affected.

[0027] According to one aspect of this disclosure, the circuit board can be heated to a temperature in the range of 60°C to 90°C before applying the liquefied solder balls. Therefore, the liquefied solder balls are not drastically cooled after reaching the surface of the circuit board, and thus remain sufficiently liquefied, allowing them to properly flow into and fill the annular gap. This results in a high filling degree of the annular gap.

[0028] According to one aspect of this disclosure, the pin can be heated before the liquefied solder ball is applied. Preferably, the pin can be heated by directing a laser beam onto the pin. More preferably, a pin-heating laser beam having a wavelength of light suitable for the absorption characteristics of the pin (i.e., the material used to manufacture the pin) is directed onto the pin. In particular, the pin-heating laser beam is a blue laser beam. For example, the light of the pin-heating laser beam may have a wavelength in the range of 450 nm to 475 nm, especially 450 nm. In this way, when the liquefied solder ball reaches the pin, the solidification of the liquefied solder ball can be delayed, allowing a portion of the liquefied solder ball to properly flow in and fill the annular gap. Therefore, a high fill degree of the annular gap can be achieved, and thus a proper engagement between the pin and the via can be achieved.

[0029] According to an additional aspect of this disclosure, the temperature of the pin can be measured during heating. Heating of the pin is stopped if the pin temperature exceeds a predetermined threshold temperature. In this way, overheating of the pin or electronic components connected to the pin is avoided.

[0030] According to another aspect of this disclosure, the duration for heating the pin can be predetermined. For example, the duration can be predetermined by conducting an experiment. This prevents the pin or the electronic components connected to the pin from overheating.

[0031] According to one aspect of this disclosure, an inert gas can be applied passively or actively to the via. The inert gas can be nitrogen, argon, helium, or formaldehyde. Therefore, solder oxidation is avoided, thereby positively influencing the soldering of the leads to the via.

[0032] According to one aspect of this disclosure, the electronic components and the circuit board can be spaced apart from each other, thereby forming an exhaust channel between the electronic components and the circuit board. This can be achieved by maintaining the electronic components and the circuit board at a distance or by arranging a spacer between the electronic components and the circuit board. Therefore, gas present in the annular gap, such as inert gas or air, can be discharged from an opening in a through-hole on the side opposite to the side where the liquefied solder ball is applied to the circuit board. Thus, portions of the liquefied solder ball can more easily flow into and fill the annular gap to achieve a high fill ratio.

[0033] The computer program product according to this disclosure includes instructions for performing the methods according to this disclosure. Therefore, the instructions cause a computer or control unit to perform the methods according to this disclosure.

[0034] The computer-readable medium according to this disclosure stores a computer program product according to this disclosure. Therefore, the CPU or control unit of a computer can read instructions from the computer-readable medium to perform the steps of the method according to this disclosure.

[0035] An apparatus for soldering electronic components having pins inserted into through-holes to a circuit board having through-holes includes a solder ball application device for applying, particularly spraying, liquefied solder balls onto the circuit board, such that a portion of the liquefied solder balls flows into and fills the annular gap between the pins and the through-holes. An apparatus for applying, particularly spraying, solder balls is disclosed in WO 02 / 28 588A1, the contents of which are incorporated herein by reference. Specifically, the solder ball application device includes a capillary movable relative to the circuit board (i.e., the annular gap) and a pressurized gas source for supplying pressurized gas into the capillary to apply (particularly spray) the liquefied solder balls onto the circuit board. By using the aforementioned solder ball application device, it is not necessary to advance the capillary into or out of the pins and through-holes, thereby increasing the speed of the soldering process.

[0036] According to one aspect of this disclosure, the apparatus may include a control unit and a drive unit for controlling and driving the solder ball application device. The control unit includes a CPU, a memory, and an input / output unit. The memory includes a computer-readable medium storing a computer program product including instructions for executing the method according to this disclosure. The drive unit is an electromechanical device for positioning the capillary of the solder ball application device relative to a circuit board (i.e., relative to an annular gap).

[0037] According to one aspect of this disclosure, the capillary can be regenerated toward the opening such that the inner diameter of the capillary is smaller than the diameter of the solid solder ball used to generate the liquefied solder ball. Therefore, it prevents the solid solder ball from falling out of the capillary.

[0038] According to one aspect of this disclosure, the capillary can be tilted relative to the surface of the circuit board. The capillary can be tilted at a fixed angle or a variable angle, which can be set by using a drive unit. Therefore, liquefied solder balls can be easily applied to the circuit board.

[0039] According to one aspect of this disclosure, the apparatus may include an energy supply unit for supplying energy to solid solder balls to produce liquefied solder balls. Thus, when pressurized gas is supplied to the capillary, the solid solder balls can be sufficiently liquefied to be ejected from the regenerated capillary.

[0040] According to a preferred aspect of this disclosure, the energy supply unit can be a laser beam, i.e., a laser source. Preferably, the laser beam is a near-infrared laser beam that can provide 200W to 400W NIR. More preferably, the laser beam is adapted to be supplied continuously or intermittently. The power and duration of the laser beam are controlled by a control unit, and the laser beam can be guided through a capillary such that the laser beam is pointed in the same direction as the capillary. Therefore, the laser beam can be appropriately applied to the solid solder ball to produce a liquefied solder ball, and can also be used to keep the liquefied solder ball sufficiently liquefied. Since the direction of the laser beam is the same as the direction of the capillary, the laser beam can still reach the liquefied solder ball after it exits the capillary. Therefore, the laser beam can be applied to the liquefied solder ball during its flight from the capillary to the circuit board or after the liquefied solder ball has reached the circuit board. Therefore, it can be ensured that a portion of the liquefied solder ball flows properly into the annular gap, thereby achieving a high fill factor.

[0041] According to one aspect of this disclosure, the device may include a temperature measuring unit for measuring the temperature of liquefied or solid solder balls. Preferably, the temperature measuring unit may be composed of an infrared sensor, and optionally an optical infrared sensor. Thus, the temperature can be transmitted from the temperature measuring unit to the control unit, and the energy supply unit, particularly the laser beam, can be appropriately controlled to prevent the liquefied solder balls from burning or to prevent the liquefied solder balls from solidifying before flowing into and filling the annular gap.

[0042] According to one aspect of this disclosure, the device may include a holding unit for holding a circuit board and an electronic component such that the pins of the electronic component are inserted into through-holes in the circuit board. Preferably, the holding unit may clamp the electronic component and the circuit board separately and insert the pins of the electronic component into the through-holes. In particular, the holding unit may be adapted to hold the electronic component and the circuit board such that the electronic component is arranged on a first side of the circuit board and liquefied solder balls are applied from a second side opposite the first side. More preferably, the holding unit may be adapted to hold the electronic component and the circuit board such that liquefied solder balls are applied downwards. Alternatively, the holding unit may be adapted to hold a circuit board on which electronic components are pre-assembled.

[0043] According to one aspect of this disclosure, the device may include a volume measuring unit for measuring the volume of solidified solder outside the via. Preferably, the volume measuring unit comprises a three-dimensional inspection device, such as a 3D scanner, and a control unit that receives captured images and performs three-dimensional image processing to determine the volume of solidified solder outside the via. Alternatively, a white light interferometer or a light field camera may be used as the three-dimensional inspection device. Therefore, the volume of solidified solder flowing into the annular gap can be determined by subtracting the measured volume of solidified solder outside the via from the total volume of the solid solder ball. It should be noted that the volume of the pins above the circuit board needs to be subtracted from the volume determined by the three-dimensional image processing to determine the volume of solder outside the via. Since the dimensions and volumes of the pins and vias are known, the volume of the annular gap can be calculated. The fill factor of the annular gap can then be determined by dividing the volume of liquefied solder flowing into the annular gap by the volume of the annular gap. Note that the above calculation can be performed by the control unit. Therefore, the device according to this disclosure can inspect the fill factor of the annular gap on-site without requiring X-ray inspection or cross-sectional inspection. Therefore, the time required to inspect the quality of weld joints can be reduced.

[0044] According to an optional aspect of this disclosure, the apparatus may include a flux application unit for applying flux to the leads and vias. This prevents oxidation of the leads and vias, thus achieving proper bonding between the leads and vias.

[0045] According to a preferred aspect of this disclosure, the energy supply unit, particularly the laser beam, can be used to activate the flux, especially by heating the flux to a temperature up to 60°C to 130°C. Therefore, the welding process can be positively influenced.

[0046] According to a preferred aspect of this disclosure, the device may include a circuit board heating unit for heating the circuit board, particularly to a temperature of 60°C to 90°C. The circuit board heating unit may supply warm air or may be a heated component in contact with the circuit board. The heated component in contact with the circuit board is preferably included in a holding unit. This prevents the liquefied solder balls from cooling upon reaching the surface of the circuit board. Therefore, it ensures that a portion of the liquefied solder balls properly flows in and fills the annular gap.

[0047] According to one aspect of this disclosure, the device may include a pin heating unit for heating the pin. The pin heating unit may be the aforementioned laser beam for liquefying solid solder balls. The laser beam can be directed to the pin through a capillary and is turned on when no solid solder ball is placed in the capillary. Preferably, the pin heating unit may be a pin-heating laser beam capable of emitting light with a wavelength suitable for the absorption characteristics of the pin (i.e., the material of the pin). It has been found that blue lasers, such as lasers with wavelengths in the range of 450 nm to 475 nm, particularly 450 nm, are most suitable for heating pins. Therefore, when the liquefied solder ball reaches the pin, the solidification of the liquefied solder ball is delayed, allowing a portion of the liquefied solder ball to properly flow in and fill the annular gap.

[0048] According to an additional aspect of this disclosure, the temperature measuring unit is adapted to measure the temperature of the pin during heating. A temperature threshold for the pin can be predetermined and stored in the control unit. The control unit is adapted to compare the temperature threshold with a temperature value obtained from the temperature measuring unit. If the control unit receives a temperature value from the temperature measuring unit that exceeds the temperature threshold, the control unit can stop heating the pin by turning off the laser beam or the pin-heating laser beam.

[0049] According to another aspect of this disclosure, the duration for which the pin is heated can be predetermined. The duration can be determined, for example, experimentally. In this way, overheating of the pin or the electronic components connected to the pin can be avoided.

[0050] According to one aspect of this disclosure, the device may include an inert gas supply unit for actively or passively supplying inert gas to the vias and leads. According to an alternative aspect, the device may be placed in a chamber or container containing an inert gas atmosphere. Therefore, oxidation of the liquefied solder is avoided, thereby having a positive impact on the soldering process.

[0051] According to one aspect of this disclosure, the holding unit is adapted to hold the circuit board and electronic components such that the electronic components and the circuit board are spaced apart from each other, thereby forming an exhaust channel between the electronic components and the circuit board. Therefore, the gas present in the annular gap, i.e., inert gas or air, can exit the annular gap to reduce resistance to the liquefied solder balls as they reach the circuit board and flow into and fill the annular gap. Thus, a high filling degree of the annular gap can be achieved. Attached Figure Description

[0052] Preferred embodiments of the present disclosure are described below with reference to the accompanying drawings. In the drawings:

[0053] Figure 1 An apparatus for soldering an electronic component having pins inserted into a through-hole to a circuit board having a through-hole, according to a first embodiment of the present disclosure, is illustrated schematically.

[0054] Figure 2 An apparatus according to a second embodiment of the present disclosure is schematically shown, the apparatus including a 3D scanner as a three-dimensional inspection device for measuring the volume of solidified solder outside a through-hole in order to determine the fill degree of the annular gap between the pin and the through-hole;

[0055] Figure 3 A variant of the device according to the second embodiment is schematically shown, which includes an interferometer that emits a measurement beam as a three-dimensional detection device;

[0056] Figure 4 The diagram schematically illustrates the definition of the size parameters of the truncated cone of solidified solder outside the through-hole, the lead, and the through-hole.

[0057] Figure 5 An apparatus according to a third embodiment of the present disclosure is schematically shown, wherein the capillary is tilted relative to the circuit board;

[0058] Figure 6 A variation of the device according to the third embodiment is schematically shown, which is capable of changing the angle of the capillary relative to the circuit board;

[0059] Figure 7 An apparatus according to a fourth embodiment of the present disclosure is schematically shown, wherein a gap is formed between a circuit board and electronic components;

[0060] Figure 8 An apparatus according to a fifth embodiment of the present disclosure is schematically shown, the apparatus including a pin-heating laser beam for heating pins;

[0061] Figure 9 An apparatus according to a sixth embodiment of the present disclosure is schematically shown, which emits a laser beam after liquefied solder has reached the circuit board and flowed into the annular gap.

[0062] Wherein: 1-Electronic component; 2-Circuit board; 3-Through hole; 4-Pin; 5-Liquefied solder ball; 6-Capillary; 7-Laser beam; 8-Solder; 8a-Solder outside the through hole; 8b-Solder inside the through hole; 9-Infrared sensor; 10-Inert gas; 11-Exhaust channel; 12-3D scanner; 13-Interferometer; 14-Measuring beam; 15-Pin heating laser beam; a-Through hole diameter; b-Through hole depth; c-Pin diameter; d-Pin height above the circuit board; e-Diameter of the truncated cone base; f-Diameter of the truncated cone top; g-Height of the truncated cone. Detailed Implementation

[0063] Figure 1An apparatus for soldering an electronic component 1 having pins 4 to a circuit board 2 having through holes 3, according to a first embodiment of the present disclosure, is shown. The pins 4 of the electronic component 1 are inserted into the through holes 3. Therefore, the electronic component 1 corresponds to a through-hole device (THD). In this embodiment, the three pins 4 of the electronic component 1 protrude substantially vertically upward from the surface of the electronic component 1, i.e., from the surface of the housing of the electronic component 1. The pins 4 protrude from the first side of the circuit board 2 (i.e., Figure 1 The pin 4 is inserted into three corresponding through holes 3 formed in the circuit board 2 from the lower side of the circuit board 2, so that the pin 4 is inserted from the second side of the circuit board 2 opposite to the first side (i.e., the lower side of the first side of the circuit board 2). Figure 1 The upper side of the pin 4 protrudes. It should be noted that this disclosure is not limited to three pins 4; the electronic component 1 may include at least one pin, two or more pins. Furthermore, the pin 4 may be tilted relative to the pins of the electronic component 1 from its protruding surface, and the pin 4 may include a bent structure. Similarly, the circuit board 2 may include a plurality of through holes 3, the number of through holes corresponding at least to the number of pins 4 on the electronic component 1. Furthermore, the through holes 3 are arranged on the circuit board 2 such that the positions of the through holes correspond to the positions of the pins 4 on the electronic component 1.

[0064] By spraying liquefied solder balls 5 onto the circuit board 2, a portion of the liquefied solder balls 5 flows into and fills the annular gap formed between the pin 4 and the through-hole 3, thereby bonding the pin 4 to the through-hole 3. After the portion of the liquefied solder balls 5 flows into the annular gap, this portion solidifies due to the ambient temperature below the melting point of the solder. Therefore, a conductive joint is formed between the pin 4 and the through-hole 3, and thus a conductive joint is formed between the pin 4 and the lead of the circuit board 2 connected to the through-hole 3.

[0065] exist Figure 1 In the illustrated embodiment, the liquefied solder balls 5 are specifically generated and sprayed using a solder ball application device comprising a regenerated capillary 6 with an opening facing the capillary 6. Specifically, the diameter of the opening of the capillary 6 is smaller than the diameter of the solid solder ball (not shown) used to generate the liquefied solder balls 5. Therefore, the solid solder ball is held at a position where the diameter of the regenerated capillary 6 corresponds to the diameter of the solid solder ball.

[0066] To direct the liquefied solder ball 5 towards the point to be welded, i.e., the annular gap, pressure is applied to the capillary 6 by a pressurized gas source, and a laser beam 7 from a laser source supplies energy to the solid solder ball to generate the liquefied solder ball 5. Therefore, as... Figure 1 As shown, the laser beam 7 is guided through the capillary 6. When the solid solder ball is fully liquefied, the liquefied solder ball 5 can deform due to the pressure within the capillary 6, allowing it to leave the capillary 6 and be ejected from the capillary 6 onto the circuit board 2 (i.e., the annular gap). Therefore, the capillary 6 does not need to advance to or exit from the circuit board 2 to apply the liquefied solder ball 5. Figure 1 The capillary tube is precisely pointed to the tip of pin 4, but it is also possible to point the capillary tube 6 to a point inside the circumference of the through hole 3 other than pin 4.

[0067] To control and move the capillary tube and control the laser beam 7, i.e., the applied power and duration of the laser beam 7, and the gas pressure source, the device includes a control unit and a drive unit (not shown). The control unit is implemented by a computer including a CPU, a memory, and an input / output unit. The memory stores a control program, which is executed by the CPU and includes instructions for executing the method according to this disclosure. The drive unit is implemented by an electromechanical actuator for driving the capillary tube 6 and other units of the device, such as a holding unit (not shown) for holding the electronic components 1 and / or the circuit board 2.

[0068] exist Figure 1 In the illustrated embodiment, liquefied solder balls 5 are sprayed onto the circuit board 2 from a second side, which is opposite to the first side where electronic components 1 are arranged. Figure 1 In this configuration, liquefied solder balls 5 are sprayed downwards. It should be noted that in this specification, downwards is defined as the direction of gravity. This arrangement provides the advantage that the liquefied solder balls 5 can easily reach the through-hole 3, and the portion of the liquefied solder balls 5 flowing into the annular gap between the pin 4 and the through-hole 3 is supported by gravity. Therefore, the solder fill of the annular gap can be increased compared to spraying the liquefied solder balls 5 upwards. To prevent electronic components 1 from falling off the circuit board 2, the device includes a holding unit (not shown) that holds at least electronic components 1 and circuit board 2. The holding unit can be adapted to hold multiple electronic components 1 and circuit board 2 individually. Alternatively, electronic components 1 and circuit board 2 can be pre-assembled using adhesive, and the holding unit can be adapted to hold only circuit board 2.

[0069] It should be noted that the supply of laser beam 7 is not limited to the case where the liquefied solder ball 5 is inside the capillary tube 6, and laser beam 7 can also be applied continuously or intermittently after the liquefied solder ball 5 is ejected from the capillary tube 6 to ensure that the liquefied solder ball 5 remains fully liquefied. Laser beam 7 is specifically supplied as the liquefied solder ball 5 flies from the capillary tube 6 towards the surface of the circuit board 2 to ensure that the liquefied solder ball 5 is still liquefied when it reaches the circuit board 2.

[0070] Furthermore, infrared sensor 9 is used to measure the temperature of the liquefied solder ball 5. Therefore, infrared sensor 9 corresponds to the temperature measurement unit and is communicatively connected to the control unit, transmitting the measured temperature of the liquefied solder ball 5 to the control unit. Thus, laser beam 7 can be controlled by the control unit to maintain the temperature of the liquefied solder ball 5 within a predetermined temperature range defined by an upper and lower temperature threshold. If the temperature of the liquefied solder ball 5 becomes higher than the upper temperature threshold, the supply of laser beam 7 is stopped or the power of laser beam 7 is set to a lower value. Therefore, combustion of the liquefied solder can be avoided. Similarly, if the temperature of the liquefied solder becomes lower than the lower temperature threshold, laser beam 7 is resupplyed to the liquefied solder ball 5, or the power of the laser beam can be set to a higher value. In this way, it is ensured that the liquefied solder ball 5 is fully liquefied, allowing a portion of the liquefied solder ball to properly flow into the annular gap. Therefore, proper engagement between pin 4 and via 3 can be ensured.

[0071] According to this disclosure, inert gas 10 is applied to the points to be soldered, i.e., to the via 3 and the pin 4. This can be achieved by actively applying inert gas 10, for example, by supplying inert gas through a capillary 6 connected to an inert gas source. Thus, the capillary 6 corresponds to an inert gas supply unit. However, the device may include an inert gas supply unit separately from the capillary 6, such as a separate nozzle. In another embodiment, inert gas 10 can be passively applied by placing the device for soldering pin 4 to via 3 in a closed environment filled with inert gas 10. Therefore, oxidation of the solder, pin 4, and / or via 3 can be avoided, and this has a positive impact on the soldering process.

[0072] After the liquefied solder ball 5 reaches the circuit board 2, it flows into and fills the annular gap between the pin 4 and the through-hole 3. To allow a portion of the liquefied solder ball 5 to properly flow into the annular gap, the circuit board 2 can be heated to prevent the liquefied solder ball 5 from solidifying upon arrival at the circuit board 2. The circuit board 2 can be heated using a circuit board heating unit, such as a blower supplying heated air or a component that contacts the circuit board 2. Preferably, the circuit board heating unit that contacts the circuit board 2 is included in a holding unit for holding the electronic component 1 and the circuit board 2.

[0073] Figure 1 The annular gap, already filled with solidified solder 8, is shown. In this embodiment, the volume of the solid solder ball and the volume of the liquefied solder ball 5 are larger than the volume of the annular gap, so not all the solder flows into the annular gap. Therefore, a portion of the liquefied solder ball 5 flows into and fills the annular gap, while another portion remains outside the through-hole.

[0074] The device according to this disclosure provides the additional benefit that, by using a solder ball application device, an SMD (surface mount device) disposed on the first side can be soldered to a circuit board, the circuit board can then be flipped, and a THD (i.e., an electronic component 1 having pins 4 inserted into a through hole 3 of a circuit board 2) can be soldered to a circuit board 2 as described above.

[0075] More preferably, at least one THD is disposed on the first side such that the pin protrudes from the second side, and liquefied solder balls 5 are applied from the second side. Furthermore, an SMD is disposed on the second side (i.e., the upper side) of the circuit board 2 and is also soldered to the circuit board 2. Then, the circuit board 2 is flipped so that the first side is above the second side, and the THD device is disposed on the second side such that the pin 4 protrudes from the first side. Then, liquefied solder balls 5 are applied to the first side to solder the pin 4 to the through-hole 3. Furthermore, an SMD is disposed on the first side and is also soldered to the circuit board using liquefied solder balls 5. In this manner, a hybrid package circuit board with electronic components (i.e., SMD and THD) on both sides of the circuit board can be easily manufactured without using a second soldering method, such as reflow soldering or selective soldering.

[0076] Figure 2 An apparatus according to a second embodiment of the present disclosure is shown, comprising a 3D scanner 12 as a three-dimensional inspection device. In this embodiment, the volume of solidified solder 8a outside the through-hole 3 is measured by using three-dimensional image processing. It should be noted that image processing methods known in the prior art for three-dimensional reconstruction can be used in this disclosure. The 3D scanner 12 may be included in the same housing as the infrared sensor 9, or may be provided separately. The 3D scanner 12 is connected to a control unit, in which image processing for determining the volume of solidified solder 8b outside the through-hole is performed. Thus, the 3D scanner 12 and the control unit correspond to a volume measurement unit. It should be noted that the three-dimensional image processing may also be performed by a computer different from the control unit.

[0077] also, Figure 2 The annular gap filled with solidified solder 8 is shown in detail. As mentioned above, the volume of the liquefied solder ball 5 is preferably larger than the volume of the annular gap. In this disclosure, the fill degree of the annular gap must be at least 70% to ensure proper electrical and mechanical bonding between the pin 4 and the through-hole 3.

[0078] According to this disclosure, when a predetermined volume of solder (i.e., the volume of liquefied solder ball 5 corresponding to the volume of solid solder ball) is applied to the circuit board 2, the filling degree of the annular gap can be determined by measuring the volume of solidified solder 8a outside the through hole 3.

[0079] To determine the fill factor, the control unit can be configured to perform the following process: The measured volume of solidified solder 8a is compared with the total volume of liquefied solder balls 5 before application to determine the volume of solder 8b flowing and solidifying in the annular gap. In this regard, it should be noted that when determining the volume of solder 8a outside the via 3, the volume of the pins 4 outside the via 3 needs to be considered. The dimensions of the pins 4 and the via 3 are known in advance, for example, from the specifications of the electronic component 1 and the circuit board 2. Therefore, the volume of the annular gap can also be determined by subtracting the volume of the pins 4 inside the via 3 from the volume of the via 3. Then, the volume of solidified solder 8b inside the annular gap is divided by the volume of the annular gap to determine the fill factor. In cases where some solder flows out from the opening of the via on the lower side, the determined volume of solidified solder 8b may even be greater than the volume of the annular gap. In this case, the fill factor is determined to be 100%.

[0080] The determined volume, fill degree, and captured image results are stored in the memory of the control unit. Therefore, this disclosure enables on-site inspection of weld joint quality without the use of X-ray inspection or cross-sectional inspection by determining the fill degree of the annular gap.

[0081] Figure 3 A variation of the second embodiment is shown, in which the interferometer 13 emitting the measurement beam 14 is used as a three-dimensional inspection device to detect the volume of solidified solder 8a outside the through-hole 3, thereby determining the fill degree. Therefore, the interferometer 13 and the control unit correspond to the volume measurement unit.

[0082] Figure 4 The parameters of the through-hole 3, the pin 4, and the solidified solder 8a outside the through-hole 3 are defined. In particular, the inventors have discovered that the solidified solder 8a can be approximately considered as a truncated cone. When the height d of the pin above the circuit board is less than the height g of the solidified solder 8a, the solidified solder 8a has a conical shape.

[0083] Furthermore, the inventor has discovered that, Figure 4 The ratios of the different parameters shown should be within the range described in the table below to obtain good results, i.e., a fill factor of 70% or greater.

[0084]

[0085] As shown in the table above, the ratio of the diameter a of the through-hole 3 to the depth b of the through-hole 3 can be in the range of 0.5 to 3. Preferably, the ratio should be 1. Additionally, the diameter a of the through-hole 3 can be 1.5 to 3 times the diameter c of the pin 4. Preferably, the diameter a of the through-hole 3 should be 2 times the diameter c of the pin 4. Furthermore, the height d of the pin 3 above the surface of the circuit board 2 should be 0 or equal to or less than 0.5 times the diameter a of the through-hole 3. Furthermore, the diameter e of the base of the solder 8a outside the through-hole 3 can be 1.5 to 2 times the diameter a of the through-hole 3. Most preferably, after soldering, the fill power of the through-hole 3 can be equal to or greater than 0.7 times the volume of the annular gap formed between the pin 4 and the through-hole 3. By setting the above ratios, the solidified solder 8 between the pin 4 and the through-hole 3 can achieve proper mechanical bonding and provide good electrical connection.

[0086] As described above, the control unit and the 3D scanner 12 or interferometer 13 measure the volume of the solidified solder 8a outside the through-hole 3, i.e., the size of the truncated cone or conical shape. The dimensions of the pin 4 and the through-hole 3 are known from the specifications of the electronic component 1 and the circuit board 2. Therefore, the control unit is able to calculate the fill degree of the annular gap by performing the following calculations.

[0087] Specifically, the volume V of the truncated cone fc The volume can be calculated using equation (1). It should be noted that when the height d of the pin 4 above the circuit board 2 is less than the height g of the solidified solder 8a outside the through-hole 3, f in equation (1) is 0, thus equation (1) corresponds to the equation used to calculate the volume of the cone. It should be noted that in the following description, the truncated cone is merely an example, and the volume of the solder 8a outside the annular gap can also be determined using three-dimensional image processing.

[0088]

[0089] The volume V of pin 4 above circuit board 2 pin It can be calculated using equation (2). Note that pin 4 will be considered a cylinder in the following text. For other geometries of pin 4, the volume of pin 4 above circuit board 2 needs to be calculated accordingly:

[0090]

[0091] By the volume V of the truncated cone fc Subtract the volume V of pin 4 above circuit board 2 pin Equation (3) can be used to calculate the volume V of the solidified solder 8a outside the through hole 3. so .

[0092] V so =V fc -Vpin Equation (3)

[0093] Due to the volume of the solid solder ball and therefore the volume V of the liquefied solder ball 5 sb Since it is known in advance, the volume V of the solidified solder 8b inside the annular gap can be calculated using equation (4). si :

[0094] V si =V sb -V so Equation (4)

[0095] In addition, the volume V of the annular gap ag It can be calculated using the following equation (5). Similarly, pin 4 is considered to be a cylinder:

[0096] V ag =π·b·(a 2 -c 2 Equation (5)

[0097] Finally, by changing the volume V of the annular gap ag Divide by the volume V of the solidified solder 8b inside the through hole 3 si To calculate the fill factor F (see equation (6)):

[0098]

[0099] It should be noted that liquefied solder may flow out from the annular gap on the side opposite to where the liquefied solder ball 5 was applied. In this case, a value greater than 100% can be calculated as the fill power F. However, the fill power F is then considered as 100%.

[0100] Figure 5 An apparatus according to a third embodiment of this disclosure is shown. Figure 3 The equipment shown is based on Figure 1 The difference in the device of the first embodiment shown is that the capillary 6 is arranged at an angle α relative to the surface of the circuit board 2. Therefore, the liquefied solder balls 5 are applied at an angle α. Figure 2 In this embodiment, the tilt angle α is 45°. However, the tilt angle α is not limited to this angle and can be in the range of 30° to 60° relative to the surface of the circuit board 2. This embodiment provides the effect that the liquefied solder ball 5 can be applied to the point where the pin 4 leaves the via, so that the liquefied solder ball flows in properly and fills the annular gap. Therefore, a high filling degree of the annular gap can be achieved.

[0101] Figure 6A variation of the third embodiment is shown, in which the capillary 6 is tilted using a drive unit controlled by a control unit. Therefore, the capillary 6 can be tilted according to the point to be welded. Figure 6 In position 1, the capillary 6 is perpendicular to the circuit board 2. In positions 2 and 3, the capillary is tilted at angles α1 and α2, respectively. Specifically, the different angles of the capillary 6 are important when the liquefied solder ball 5 is applied to a side of the circuit board 2 that already contains electronic components (such as SMDs). Furthermore, since this disclosure can be used for hybrid packaged circuit boards, it may be necessary to change the application angle in order to solder other electronic components, such as SMDs, onto the circuit board. Therefore, this embodiment can properly engage the pin 4 and the via 3, and can easily package hybrid packaged circuit boards.

[0102] Figure 7 An apparatus according to a fourth embodiment of this disclosure is shown. Figure 7 The equipment shown is Figure 1 The difference in the device shown is that the electronic component 1 and the circuit board 2 are separated from each other, forming an exhaust channel 11 between them. Therefore, when the liquefied solder ball 5 reaches the through hole 3, the gas present in the annular gap, i.e., the inert gas 10 or air, can be released onto the opposite side of the circuit board 2. Figure 7 The liquefied solder ball 5 flows out from the lower side of the annular gap. Therefore, when the liquefied solder ball 5 flows into the annular gap, the resistance of the liquefied solder ball is reduced, thereby ensuring proper filling of the annular gap. To form the exhaust channel 11, the retaining unit can be adapted to hold the electronic component 1 and the circuit board 2 apart from each other. Alternatively, more than one spacer can be arranged between the electronic component 1 and the circuit board 2. It should be noted that the fourth embodiment shows a capillary 6 according to the first embodiment, which is not inclined relative to the surface of the circuit board 2; however, the fourth embodiment can also be combined with the third embodiment, wherein the capillary 6 is inclined at a fixed or variable angle relative to the surface of the circuit board 2.

[0103] Figure 8 A fifth embodiment of this disclosure is shown. As mentioned in the description of the first embodiment, the circuit board 2 can be heated by using a heating unit. Alternatively, the device according to the fifth embodiment may include a pin heating unit. Figure 8As shown, the pin heating unit is formed by a pin heating laser beam 15, which is different from the laser beam 7 used to liquefy solid solder balls to produce liquefied solder balls 5. Preferably, the pin heating laser beam 15 can be guided through a capillary and concentrated on the pin 4. Therefore, the pin heating laser beam 15 can have a smaller diameter than the laser beam 7. Furthermore, the pin heating laser beam 15 has a wavelength different from that of the laser beam 7, and this wavelength is suitable for the absorption characteristics of the pin 4 (i.e., the material of the pin 4). In particular, the pin heating laser beam 15 is a blue laser beam, and the wavelength of the pin heating laser beam 15 is approximately 450 nm. However, the pin laser beam can also have a larger wavelength up to 475 nm. By heating the pin 4 before applying the liquefied solder balls 5, the solidification of the liquefied solder is delayed, especially the solidification of the solder flowing into the annular gap, so that a larger portion flows into and fills the annular gap between the pin 4 and the via 3. In this way, a higher fill factor can be achieved, and therefore a better bond can be achieved between the pin 4 and the via 3. It should be noted that the laser beam 7 can also be used to heat the pin 4. However, since the wavelength of laser beam 7 is not suitable for pin 4, it may take longer to heat pin 4.

[0104] Furthermore, the above embodiments are not limited to applying the pin heating laser beam 15 to the pin before applying the liquefied solder ball 5. When the height of the pin 4 is higher than the height of the solder 8a outside the via, the pin heating laser beam 15 may also be applied to the pin 4 after the liquefied solder ball 5 has reached the circuit board 2 and a portion of the liquefied solder has flowed into the annular gap.

[0105] According to the fifth embodiment, the duration for which pin 4 is heated can be predetermined. The duration can be determined, for example, through experimentation. In this way, overheating of pin 4 or the electronic component 1 connected to the pin can be avoided.

[0106] Furthermore, the fifth embodiment can be combined with the first embodiment, which includes an infrared sensor 9 as a temperature measurement unit. The infrared sensor 9 can then be adapted to additionally measure the temperature of pin 4 during heating. A temperature threshold for pin 4 can be predetermined and stored in the control unit. The control unit can be adapted to compare the temperature threshold with the temperature value obtained from the infrared sensor 9. If the control unit receives a temperature value exceeding the temperature threshold from the temperature measurement unit, the control unit can stop heating pin 4 by turning off the pin heating laser beam 15.

[0107] Figure 9A sixth embodiment of this disclosure is shown, wherein a laser beam 7 is applied to solder 8, which has reached the circuit board and a portion of the solder has flowed into the annular gap. The time to reach the surface of the circuit board 2 can be calculated based on the distance between the capillary 6 and the surface of the circuit board 2 and the pressure inside the capillary 6, or determined empirically. Alternatively, the arrival time can be detected by image recognition.

[0108] By applying laser beam 7 after it reaches circuit board 2, the solder 8 remains liquefied, allowing it to further flow into the annular gap, such as... Figure 9 As indicated by the arrow in the diagram. Since pin 4 can protrude from the solder 8 outside the annular gap, pin 4 can also be heated by the laser beam 7. Preferably, the temperature of the solder 8 is measured using an infrared sensor 9, and the application of the laser beam 7 is stopped by a control unit if the temperature of the solder exceeds a predetermined threshold. Alternatively, the laser beam 7 can be applied for a predetermined time, which has been predetermined, for example, through experimentation. In this way, burning of the solder 8 can be avoided. In summary, the sixth embodiment enables a higher fill degree of the annular gap because the solder remains liquefied after reaching the circuit board.

[0109] Furthermore, the fifth and sixth embodiments can be combined. Therefore, the pin 4 is preheated using the pin-heating laser beam 15, and the solder 8 remains liquefied after the liquefied solder ball 5 reaches the circuit board 2. Furthermore, if the height of the pin 4 is higher than the height of the solder 8a outside the via, the laser beam 7 and the pin-heating laser beam 15 can be applied simultaneously after the liquefied solder ball 5 reaches the circuit board. Most preferably, the pin-heating laser beam 15 is then focused on the pin 4.

[0110] The first to sixth implementation schemes have been described above. It should be noted that different implementation schemes can be combined. For example, the first implementation scheme can be combined with the second, fourth, fifth, and sixth implementation schemes. Furthermore, the third implementation scheme can be combined with the second, fourth, fifth, and sixth implementation schemes.

Claims

1. A method for soldering an electronic component (1) having pins (4) to a circuit board (2) having through holes (3), wherein the pins (4) are inserted into the through holes (3), wherein A liquefied solder ball (5) is applied to the circuit board (2), such that a portion of the liquefied solder ball (5) flows into and fills the annular gap between the pin (4) and the through hole (3). The feature is that, after the portion of the liquefied solder ball (5) has filled the annular gap, the filling degree of the annular gap is determined by measuring the volume of solidified solder (8a) outside the through hole (3) based on the predetermined total volume of the liquefied solder ball (5) before application.

2. The method according to claim 1, characterized in that, The liquefied solder ball (5) is applied to the circuit board (2) from the side opposite to the side of the circuit board (2) where the electronic component (1) is arranged.

3. The method according to claim 2, characterized in that, The liquefied solder ball (5) is applied downwards onto the circuit board (2).

4. The method according to claim 3, characterized in that, The liquefied solder ball (5) is applied to the circuit board (2) at an angle (α), wherein the angle (α) is in the range of 30° to 60° relative to the circuit board (2).

5. The method according to any one of claims 2 to 4, characterized in that, The liquefied solder ball (5) is applied in the direction of the through hole (3), wherein the through hole (3) includes a point pointing to the pin (4) away from the through hole (3).

6. The method according to claim 1, characterized in that, Before applying the liquefied solder ball (5), energy is supplied to the solid solder ball to generate the liquefied solder ball (5).

7. The method according to claim 6, characterized in that, The energy is a laser beam (7) in the range of 200W to 400W NIR and is supplied for a period of 20 to 4000ms.

8. The method according to claim 7, characterized in that, During the application of the liquefied solder ball to the circuit board (2), the laser beam (7) is applied to the liquefied solder ball (5) to keep the liquefied solder ball liquefied.

9. The method according to claim 7, characterized in that, After the liquefied solder ball (5) has reached the circuit board (2), the laser beam (7) is applied to the liquefied solder to keep the liquefied solder liquefied.

10. The method according to any one of claims 6 to 9, characterized in that, The temperature of the liquefied solder ball (5) is measured while the energy is supplied. When the temperature of the liquefied solder ball (5) exceeds a predetermined upper limit temperature threshold, the energy supply is stopped, and Energy supply begins when the temperature of the liquefied solder ball (5) is lower than the predetermined lower limit temperature threshold.

11. The method according to claim 6, characterized in that, The diameter of the solid solder ball is in the range of 0.8 mm to 2.0 mm.

12. The method according to claim 1, characterized in that, Before applying the liquefied solder ball (5), the circuit board (2) is heated to a temperature range of 60°C to 90°C.

13. The method according to claim 7, characterized in that, Before applying the liquefied solder ball (5), the pin (4) is heated by a pin-heating laser beam (15) having a wavelength different from that of the laser beam (7) and adapted to the absorption characteristics of the pin (4).

14. A computer program product, characterized in that, The computer program product includes instructions for performing the method according to claim 1.

15. A computer-readable medium, characterized in that, The computer-readable medium stores the computer program product according to claim 14.

16. An apparatus for soldering an electronic component (1) having pins (4) to a circuit board (2) having through holes (3), wherein the pins (4) are inserted into the through holes (3), the apparatus comprising: A solder ball application device is used to apply liquefied solder balls (5) onto the circuit board (2), such that a portion of the liquefied solder balls (5) flows into and fills the annular gap between the pin (4) and the through hole (3). The device is characterized in that it further includes a volume measuring unit, which is used to determine the filling degree of the annular gap by measuring the volume of solidified solder (8a) outside the through hole (3) based on a predetermined total volume of the liquefied solder ball (5) before application, after the portion of the liquefied solder ball (5) has filled the annular gap.

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