An infrared thermal perspective method for detecting solder joint defects on circuit boards

Abstract

The invention discloses an infrared thermal perspective method for detecting solder joint defects of a circuit board, belonging to the technical field of solder joint quality detection of circuit boards. The specific scheme comprises the following steps: step 1, using an infrared laser to respectively irradiate a part or all of a standard cold-welded circuit board and a qualified circuit board, after stopping the irradiation, an infrared thermal imager is aligned with the position of the infrared laser irradiation spot to shoot an infrared thermal image; step 2, using an infrared laser to irradiate a part or all of the circuit board to be tested, after stopping the irradiation, an infrared thermal imager is aligned with the position of the infrared laser irradiation spot to shoot an infrared thermal image of the circuit board to be tested; the highest temperature value of a solder joint of a component on the standard cold-welded circuit board is used as the upper limit H of the temperature scale in the infrared thermal image of the circuit board to be tested, and the lowest temperature value of the solder joint of the same component on the qualified circuit board is used as the lower limit L of the temperature scale in the infrared thermal image of the circuit board to be tested, so as to obtain an infrared thermal perspective image of the component on the circuit board to be tested, and judge whether the solder joint of the component on the circuit board to be tested has defects.

Description

Technical Field

[0001] The present invention belongs to the technical field of circuit board solder joint quality detection, and specifically relates to an infrared thermal perspective method for circuit board solder joint defects, which is mainly used for electronic product production and maintenance, and further, for rapid screening and detection of product solder joint defects. Background Art

[0002] The quality inspection of solder joint defects in circuit boards has always been a headache in the field of electronic product production and maintenance. Conventional magnifying glasses and automatic optical inspection instruments (AOI) can only screen out solder joints with obvious defects on the surface, but are powerless against internal defects in solder joints. Automatic X-ray inspection instruments (AXI) can only see large air holes in solder joints, but cannot detect defects such as cold solder joints and cracks. Therefore, the production and maintenance fields often encounter such a situation that a failed circuit board often requires professionals to spend a lot of energy and time to find and identify the fault point. Especially when the circuit board failure phenomenon is sometimes good and sometimes bad, it may take professionals several days or even weeks to determine the fault point. Summary of the invention

[0003] In order to solve the problems existing in the background technology and to quickly and intuitively detect the defects of solder joints of circuit boards, the present invention provides an infrared thermal perspective method for detecting defects of solder joints of circuit boards.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] An infrared thermal perspective method for detecting solder joint defects on a circuit board comprises the following steps:

[0006] Step 1: Use infrared laser to irradiate part or all of the standard completely cold-solder circuit board and the qualified circuit board respectively. After stopping the irradiation, the infrared thermal imager is aimed at the position of the infrared laser irradiation spot to take an infrared thermal image;

[0007] Step 2: Use infrared laser to partially or completely irradiate the circuit board to be tested. After stopping the irradiation, aim the infrared thermal imager at the position of the infrared laser irradiation spot to take the infrared thermal image of the circuit board to be tested; take the highest temperature value of the solder joint of a component on the standard completely cold-solder circuit board as the upper limit H of the temperature scale in the infrared thermal image of the circuit board to be tested, and take the lowest temperature value of the solder joint of the same component on the qualified circuit board as the lower limit L of the temperature scale in the infrared thermal image of the circuit board to be tested, that is, obtain the infrared thermal perspective image of the component on the circuit board to be tested, and judge whether there is a defect in the solder joint of the component on the circuit board to be tested.

[0008] Furthermore, the standard for judging whether the solder joint has defects is as follows: comparing with the corresponding component solder joints in the infrared thermal image of the qualified circuit board, if the temperature area of ​​the solder joint in the infrared thermal image of the circuit board to be tested is not complete and uniform, then the solder joint has defects; if circular high-temperature spots appear in the local area of ​​the solder joint in the infrared thermal image of the circuit board to be tested, then there are pores in the solder joint; if the solder joint and component temperature areas in the infrared thermal image of the circuit board to be tested are not connected, then there is a cold joint between the solder joint and the circuit board.

[0009] Furthermore, the solder joints between the components and the circuit board on the standard completely cold solder joint circuit board are all completely cold solder joints; and the solder joints between the components and the circuit board on the qualified circuit board are all good solder joints.

[0010] Furthermore, the method for preparing the standard completely cold-solder circuit board comprises the following steps:

[0011] Step 1, printing solder paste on the bare circuit board;

[0012] Step 2: solder the solder paste onto the circuit board pad using a reflow furnace;

[0013] Step 3: Apply a drop of glue in the middle of the component placement area on the bare circuit board;

[0014] Step 4: Mount the components on the glue droplets, and then cure the glue droplets to obtain a standard completely cold-solder circuit board.

[0015] Furthermore, the method for preparing the qualified circuit board comprises the following steps:

[0016] S1. Print solder paste on bare circuit board;

[0017] S2. Put a drop of glue on the middle of the component placement area on the bare circuit board;

[0018] S3, mounting components on the glue drop, and then curing the glue drop;

[0019] S4. Use a reflow furnace to solder components onto the circuit board pads.

[0020] Furthermore, the maximum power of the infrared laser is 7-50 watts, and the wavelength is 808 nm or 405 nm.

[0021] Furthermore, in step 1 and step 2, before irradiating the infrared laser, the distance between the beam expander of the infrared laser and the circuit board is adjusted so that the diameter of the laser spot on the circuit board is 10-100 mm.

[0022] Furthermore, in the step 1 and the step 2, an infrared thermal imager is used to capture an infrared thermal image of the circuit board n seconds after the infrared laser stops irradiating, wherein n≤1s.

[0023] Furthermore, in step 1 and step 2, the time for the infrared laser to irradiate the circuit board is ≤10s.

[0024] Furthermore, in step 1 and step 2, after irradiation with infrared laser, the surface temperature of the circuit board and components is controlled below 100°C, while ensuring that the lowest temperature of each component is more than 10°C above room temperature.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The infrared thermal perspective method for detecting solder joint defects of circuit boards of the present invention is fast and intuitive, which helps electronic finished product manufacturers and repair manufacturers to quickly screen out defective solder joints. Compared with the method in the prior art that requires point-by-point irradiation detection and identification, it is more efficient, intuitive and simple, which helps the large-scale promotion and application of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the laser irradiation area on the circuit board;

[0028] Figure 2 This is a flow chart of the preparation method of a conventional qualified circuit board, A is a component, B is a solder joint, C is a bare circuit board, D is a glue drop, and E is solder paste;

[0029] Figure 3 This is a flow chart of the preparation method of a standard completely cold-solder circuit board. A is a component, B is a solder joint, C is a bare circuit board, D is a glue drop, and E is solder paste.

[0030] Figure 4 This is an optical schematic diagram of resistors, capacitors and diodes after welding, where A is the component and B is the welding point;

[0031] Figure 5 For good solder joints Figure 3 The infrared detection schematic diagram of resistors, capacitors and diodes is shown, where A is the component and B is the solder joint;

[0032] Figure 6 for Figure 3 Schematic diagram of infrared detection of complete cold solder joints on the left side of the resistor, capacitor and diode components and partial defects on the right side of the solder joints, where A is the component and B is the solder joint;

[0033] Figure 7 for Figure 3 Schematic diagram of infrared detection of partial defects on the left solder joints of resistors, capacitors and diodes, and large air holes on the right solder joints, where A is the component and B is the solder joint;

[0034] Figure 8 for Figure 3Schematic diagram of infrared detection of defects in the left solder joints of resistors, capacitors and diodes, where A is the component and B is the solder joint;

[0035] Fig. 9 This is an optical schematic diagram of the three-stage tube components after welding;

[0036] Fig.10 For good solder joints Figure 8 The infrared detection schematic diagram of triode components shown;

[0037] Fig.11 For solder joints with cold solder joints Figure 8 The infrared detection schematic diagram of triode components shown in the figure; the arrow indicates the cold solder joint;

[0038] Fig.12 This is an optical schematic diagram of chip components after welding;

[0039] Fig.13 For good solder joints Fig.11 The schematic diagram of infrared detection of chip components shown;

[0040] Fig.14 For solder joints with cold solder joints Fig.11 The diagram below shows the infrared detection of chip components; the arrows indicate cold solder joints.

[0041] Among them, 1 is the circuit board to be tested; 2 is the laser irradiation area; 3 is the chip components; 4 is the resistor, capacitor and diode components; 5 is the solder point pin of the chip components; 6 is the solder point of the resistor, capacitor and diode components. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be clearly and completely described below in conjunction with the drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Specific implementation method 1

[0044] The present invention uses a beam of uniform high-power infrared laser spot to illuminate the entire or part of the circuit board to be tested for m seconds. The irradiated part can be a single component or multiple components, such as Figure 1 As shown, the temperature of the components in this part rises rapidly, and the infrared thermal imager is aimed at this part to take an infrared thermal image within 1 second after the infrared laser stops irradiating. The temperature width range is set according to the solder joint situation, and a "perspective" image of the solder joint defects of each component in the picture can be obtained. By comparing it with the infrared thermal image of the components with qualified solder joints, the defective solder joints can be found. The specific plan is as follows:

[0045] An infrared thermal perspective method for detecting solder joint defects on a circuit board comprises the following steps:

[0046] Step 1: Use infrared laser to irradiate part or all of the standard completely cold-solder circuit board and the qualified circuit board respectively. After stopping the irradiation, the infrared thermal imager is aimed at the position of the infrared laser irradiation spot to take an infrared thermal image;

[0047] Step 2: Use infrared laser to partially or completely irradiate the circuit board to be tested. After stopping the irradiation, aim the infrared thermal imager at the position of the infrared laser irradiation spot to take the infrared thermal image of the circuit board to be tested; take the highest temperature value of the solder joint of a component on the standard completely cold-solder circuit board as the upper limit H of the temperature scale in the infrared thermal image of the circuit board to be tested, and take the lowest temperature value of the solder joint of the same component on the qualified circuit board as the lower limit L of the temperature scale in the infrared thermal image of the circuit board to be tested, that is, obtain the infrared thermal perspective image of the component on the circuit board to be tested, and judge whether there is a defect in the solder joint of the component on the circuit board to be tested.

[0048] Furthermore, the standard for judging whether the solder joint has defects is as follows: comparing with the corresponding component solder joints in the infrared thermal image of the qualified circuit board, if the temperature area of ​​the solder joint in the infrared thermal image of the circuit board to be tested is not complete and uniform, then the solder joint has defects; if a nearly circular high-temperature spot appears in the local area of ​​the solder joint in the infrared thermal image of the circuit board to be tested, then there are pores in the solder joint; if the solder joint and the component temperature area in the infrared thermal image of the circuit board to be tested are not connected, then there is a cold joint between the solder joint and the circuit board.

[0049] Furthermore, the solder joints between the components and the circuit board on the standard completely cold solder joint circuit board are all completely cold solder joints; and the solder joints between the components and the circuit board on the qualified circuit board are all good solder joints.

[0050] Furthermore, the method for preparing the standard completely cold-solder circuit board comprises the following steps:

[0051] Step 1, printing solder paste on a bare circuit board; the solder paste is preferably tin paste;

[0052] Step 2: solder the solder paste onto the circuit board pad using a reflow furnace;

[0053] Step 3, applying glue drops on the middle of the component placement area on the bare circuit board by a glue dispenser;

[0054] Step 4: Use a chip mounter to mount the components on the glue droplets, and then cure the glue droplets at 120℃ to obtain a standard completely cold-welded circuit board. Figure 3 shown.

[0055] The printed solder paste is wetted and spread on the pad after reflow; after dispensing and mounting and curing, the components are bonded to the circuit board by glue drops, and the pins of the components are just in contact with the solder on the pad but no metallurgical connection is formed (not soldered, the curing temperature does not reach the melting temperature of the solder paste), in order to simulate the entire circuit board with full cold solder joints (all component solder joints are completely cold solder joints).

[0056] The main functions of the standard completely cold soldered circuit board are: 1) Determine the parameters such as the power, irradiation time and irradiation area of ​​the high-power infrared laser. The basic requirements are: 1. The laser irradiation time is generally less than 10 seconds; 2. The maximum surface temperature of each component itself during the laser irradiation process generally does not exceed 100°C, and at the same time, ensure that the minimum temperature of each component is more than 10°C above the room temperature. 2) Determine the upper limit of the infrared thermal image temperature scale in the detection of the circuit board to be tested; 3) Use it as a standard sample for thermal image comparison in the detection of the circuit board to be tested.

[0057] Furthermore, the method for preparing the qualified circuit board comprises the following steps:

[0058] S1, printing solder paste on a bare circuit board; the solder paste is preferably tin paste;

[0059] S2, applying glue drops on the middle of the component placement area on the bare circuit board by a glue dispenser;

[0060] S3, use a placement machine to mount components on the glue drop, and then cure the glue drop at a low temperature of 120℃;

[0061] S4. Use a reflow furnace to solder components onto the pads of the circuit board as usual; the production process diagram is as follows Figure 2 shown.

[0062] Furthermore, the maximum power of the infrared laser can be selected to be 7-50 watts, and the wavelength is 808 nm or 405 nm.

[0063] Furthermore, in step 1 and step 2, before irradiating the infrared laser, the distance between the beam expander of the infrared laser and the circuit board is adjusted so that the diameter of the laser spot on the circuit board is 10-100 mm.

[0064] Furthermore, in the step 1 and the step 2, an infrared thermal imager is used to capture an infrared thermal image of the circuit board n seconds after the infrared laser stops irradiating, wherein n≤1s.

[0065] Furthermore, in step 1 and step 2, the infrared laser irradiates the circuit board for a time m≤10s.

[0066] The software of the infrared thermal imager will automatically adjust the temperature scale width in real time according to the highest and lowest temperatures of the entire screen. The infrared thermal images taken accordingly cannot achieve the infrared perspective effect of the solder joints.

[0067] In the present invention, the upper limit H of the temperature scale is set by the highest temperature value of the solder joint of a certain component on a standard completely cold solder joint circuit board; the lower limit L of the temperature scale is set by the lowest temperature value of the solder joint of the same component on a good and qualified circuit board. In this way, a perspective effect of the solder joint can be obtained, and the morphology of the internal defects of the solder joint can be intuitively seen.

[0068] The criteria for judging whether a solder joint is defective are:

[0069] 1) A good solder joint can be regarded as a whole metal, which is a good conductor of heat. Therefore, the temperature difference between each part of the solder joint thermal image is small and complete and uniform. Figure 5 , Fig.10 and Fig.13 ;

[0070] 2) Cold solder joints (a general term for defective solder joints relative to good solder joints) Solder joints present different perspective effects due to their different defect forms. Figure 6 , Figure 7 , Figure 8 , Fig.11 , Fig.14 The overall thermal map of the solder joint will show separation, incompleteness, uneven temperature, etc.

[0071] 2.1) Soldering points of resistors, capacitors and diodes

[0072] The infrared thermal image features of the solder joints of resistors, capacitors and diodes are shown in the figure. Figure 6 The solder joint on the left is completely divided into two parts, not a whole, and the color depth is very different (that is, the temperature difference is large).

[0073] The infrared thermal image characteristics of the internal pores in the solder joints of resistors, capacitors and diodes are shown in Figure 7 There is a dark color (high temperature) in the middle of the right solder joint, which indicates that there is a large pore inside. Such solder joints are prone to early failure during service.

[0074] Some defects in the solder joints of resistors, capacitors and diodes are shown in Figure 8 , compared with good solder joints, there are local defects, and such solder joints are prone to early failure during service.

[0075] 2.2) Soldering points of transistor components

[0076] The infrared thermal image characteristics of the virtual solder joints of transistor components are shown in Fig.11 The two arrows point to solder points where the two pins are dark in color and have a clear contrast with the light color of the solder at the top pad position (large temperature difference).

[0077] 2.3) Solder joints of chip components

[0078] The infrared thermal image characteristics of chip components solder joints are shown in Fig.14 The arrow points to the solder point, where the pin is dark in color and has a sharp contrast with the light color of the solder at the top pad (large temperature difference).

[0079] Example 1

[0080] An infrared thermal perspective method for detecting solder joint defects on a circuit board comprises the following steps:

[0081] 1) An infrared laser with a maximum power of 7 watts and a wavelength of 808 nm is selected;

[0082] 2) Adjust the distance between the infrared laser beam expander and the circuit board to obtain a uniform circular spot with a diameter of 30 mm;

[0083] 3) Aim the light spot at several components to be tested on the circuit board;

[0084] 4) Adjust the infrared thermal imager to focus on the detection area;

[0085] 5) Start the infrared laser at full power of 7 watts for 10 seconds;

[0086] 6) Start the infrared laser and infrared thermal imager linkage synchronization controller to control the infrared thermal imager to take photos synchronously after a delay of 0.5 seconds when the laser irradiation stops;

[0087] 7) First, test part or all of the standard solder joint circuit board according to steps 1) to 6) to obtain the upper limit value of the temperature scale, and the upper limit value is 67°C;

[0088] 8) Similarly, the good qualified circuit is tested in steps 1)-6) to obtain the lower limit value of the temperature scale, and the lower limit value is 34°C;

[0089] 9) Repeat steps 1) to 6) to detect the circuit board to be tested, and manually set the temperature scale to 34-67°C to obtain the infrared perspective effect image of the solder joints of the components to be tested on the circuit board;

[0090] 10) By manually comparing this infrared thermal image with the infrared thermal image of a good and qualified circuit board, you can know which solder joint is defective. Figure 4-Figure 14 ;

[0091] 11) For batch inspection of circuit boards, the infrared thermal image obtained by the inspection can be subtracted from the infrared thermal image of good and qualified circuit boards through PS software to quickly find abnormal solder joints.

[0092] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for infrared thermal perspective of solder joint defects on a circuit board, characterized by: The following steps are involved: Step 1: Use infrared laser to irradiate part or all of the standard completely cold-solder circuit board and the qualified circuit board respectively. After stopping the irradiation, the infrared thermal imager is aimed at the position of the infrared laser irradiation spot to take the infrared thermal image; Step 2: Use infrared laser to partially or completely irradiate the circuit board to be tested. After stopping the irradiation, aim the infrared thermal imager at the position of the infrared laser irradiation spot to take the infrared thermal image of the circuit board to be tested; take the highest temperature value of the solder joint of a component on the standard completely cold-solder circuit board as the upper limit H of the temperature scale in the infrared thermal image of the circuit board to be tested, and take the lowest temperature value of the solder joint of the same component on the qualified circuit board as the lower limit L of the temperature scale in the infrared thermal image of the circuit board to be tested, that is, obtain the infrared thermal perspective image of the component on the circuit board to be tested, and judge whether there is a defect in the solder joint of the component on the circuit board to be tested.

2. The infrared thermal perspective method for detecting solder joint defects of a circuit board according to claim 1, characterized in that: The criteria for judging whether a solder joint is defective are as follows: if the solder joint is compared with the corresponding component solder joint in the infrared thermal image of a qualified circuit board, if the solder joint temperature area in the infrared thermal image of the circuit board to be tested is not complete and uniform, then the solder joint is defective; if a circular high-temperature spot appears in a local area of ​​the solder joint in the infrared thermal image of the circuit board to be tested, then there is a pore in the solder joint; if the solder joint and component temperature areas in the infrared thermal image of the circuit board to be tested are not connected, then there is a cold solder joint between the solder joint and the circuit board.

3. The infrared thermal perspective method for detecting solder joint defects of a circuit board according to claim 1, characterized in that: The solder joints between the components and the circuit board on the standard completely cold solder joint circuit board are all completely cold solder joints; the solder joints between the components and the circuit board on the qualified circuit board are all good solder joints.

4. The infrared thermal perspective method for detecting solder joint defects of a circuit board according to claim 1 or 3, characterized in that: The method for preparing the standard completely cold-solder circuit board comprises the following steps: Step 1, printing solder paste on the bare circuit board; Step 2: solder the solder paste onto the circuit board pad using a reflow furnace; Step 3: Apply a drop of glue in the middle of the component placement area on the bare circuit board; Step 4: Mount the components on the glue droplets, and then cure the glue droplets to obtain a standard completely cold-solder circuit board.

5. The infrared thermal perspective method for detecting solder joint defects of a circuit board according to claim 1 or 3, characterized in that: The method for preparing the qualified circuit board comprises the following steps: S1. Print solder paste on bare circuit board; S2. Put a drop of glue on the middle of the component placement area on the bare circuit board; S3, mounting components on the glue drop, and then curing the glue drop; S4. Use a reflow furnace to solder components onto the circuit board pads.

6. The infrared thermal perspective method for detecting solder joint defects on a circuit board according to claim 1, characterized in that: The maximum power of the infrared laser is 7-50 watts, and the wavelength is 808 nm or 405 nm.

7. The infrared thermal perspective method for detecting solder joint defects of a circuit board according to claim 1, characterized in that: In step 1 and step 2, before irradiating the infrared laser, the distance between the beam expander of the infrared laser and the circuit board is adjusted so that the diameter of the laser spot on the circuit board is 10-100 mm.

8. The infrared thermal perspective method for detecting solder joint defects in a circuit board according to claim 1, characterized in that: In the step 1 and the step 2, an infrared thermal image of the circuit board is captured using an infrared thermal imager n seconds after the infrared laser stops irradiating, wherein n≤1s.

9. The infrared thermal perspective method for detecting solder joint defects in a circuit board according to claim 1, characterized in that: In step 1 and step 2, the infrared laser irradiates the circuit board for a time of ≤10s.

10. The infrared thermal perspective method for detecting solder joint defects on a circuit board according to claim 1, characterized in that: In step 1 and step 2, after irradiation with infrared laser, the surface temperature of the circuit board and components is controlled below 100°C, while ensuring that the lowest temperature of each component is more than 10°C above room temperature.

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