High-density packaging circuit board solder joint dry joint infrared rapid screening system and screening method

Abstract

An infrared rapid screening system and method for solder joint voids in a high-density packaged circuit board, belonging to the field of solder joint void detection for circuit boards. The specific solution is as follows: The screening system includes an infrared thermal imager and a heat source; the infrared thermal imager is arranged directly above the circuit board to be tested and the lens faces the circuit board to be tested, and the heat source is located beside the infrared thermal imager. The heat source is used to heat the whole or part of the circuit board to be tested. At the same time as heating stops, the infrared thermal imager takes a thermal image of the circuit board to be tested. In the thermal image of the circuit board to be tested, if the temperature of the whole or part of a certain component is higher than the set value compared to the temperature of the corresponding component in the thermal image of the standard qualified sample board, then there is a solder joint void or defect in this component. The present invention completely breaks through the industry problem of detecting solder joint voids in components of high-density packaged circuit boards. The components that can be detected cover various existing chips and resistor-capacitor components. At the same time, its high efficiency helps to apply the present invention to the production line.

Description

Technical Field

[0001] The invention belongs to the field of circuit board solder joint cold soldering detection, and in particular relates to an infrared rapid screening system and screening method for high-density packaged circuit board solder joint cold soldering. Background Art

[0002] Existing research shows that about 50% of failed electronic products are caused by the quality of solder joints on printed circuit boards. Solder joint quality problems cannot be eradicated by improving materials and processes. Existing automatic optical inspection (AOI) and automatic X-ray inspection (AXI) technologies are unable to detect solder joint defects. The detection of solder joint defects on circuit boards has always been a global problem.

[0003] The inventor has innovatively solved the problem of detecting cold solder joints on conventional circuit boards through a variety of infrared non-destructive testing methods, and has achieved the level of practical application. For example, invention patents ZL201110033883.2 "Infrared temperature measurement detection method for detecting the reliability of circuit board solder joints", ZL201110033879.6 "Detection system for detecting the reliability of circuit board solder joints using infrared multi-point temperature measurement thermal resistance method", ZL202010591848.1 "Scanning circuit board solder joint cold solder joint automatic detection system and detection method", ZL202010591847.7 "A threshold screening method and infrared detection method for circuit board solder joint quality".

[0004] With the continuous updating and progress of technology, the miniaturization of electronic products is progressing faster and faster. For example, the components installed on high-density packaging circuit boards for mobile phones are getting smaller and smaller, and the arrangement is getting denser and denser. 0201 components (i.e., the length, width and height of the components are 0.6 mm x 0.3 mm x 0.23 mm, not as big as a grain of rice) are widely used. The smallest one is the 008004 component, which is 0.25 mm x 0.125 mm x 0.125 mm. At the same time, various types of chips such as BGA are also used in large quantities on this type of circuit board, which brings great difficulties to the quality inspection of circuit board solder joints. The infrared detection methods in the prior art are all for conventional circuit boards. The laser can focus the light spot to a minimum diameter of about 0.2 mm, and use this light spot to illuminate the solder of the component solder joint to perform solder joint detection (the size of conventional solder joints is generally around several millimeters).

[0005] Obviously, the infrared detection method in the prior art cannot detect the solder joints of high-density packaged circuit boards. Not only is the light spot focusing not good (the focused light spot has high energy, and it will burn the surface when it is irradiated on components and circuit boards), but also aligning the solder joints one by one is also a big problem. In addition, the lead part is almost invisible on the circuit board (it is directly done in the middle layer), and the point-by-point scanning programming control is also a headache, which has no possibility of being applied in engineering. At present, there is no effective detection method for the problem of cold solder joints of high-density packaged circuit boards.

[0006] As is well known, mobile phone production is characterized by huge output, often reaching tens of millions or even hundreds of millions. Improving the yield rate of products at the time of leaving the factory is the unremitting pursuit of each brand under high competition. This industry is in urgent need of detection technologies and instruments that can quickly screen for solder joint voids on circuit boards. Summary of the Invention

[0007] Aiming at the problem that solder joint voids on high-density packaging circuit boards cannot be detected, the present invention proposes an infrared rapid screening system and screening method for solder joint voids on high-density packaging circuit boards.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] An infrared rapid screening system for solder joint voids on high-density packaging circuit boards, comprising an infrared thermal imager and a heat source; the infrared thermal imager is arranged directly above the circuit board to be tested and the lens faces the circuit board to be tested, and the heat source is located beside the infrared thermal imager for heating the whole or part of the circuit board to be tested.

[0010] Furthermore, the screening system further comprises a circuit board transportation mechanism, the circuit board transportation mechanism is arranged below the infrared thermal imager and the heat source, and a plurality of circuit boards to be tested are evenly placed on the circuit board transportation mechanism and pass through the heat source and the infrared thermal imager in sequence.

[0011] As a preferred example, the heat source is two infrared lasers I, the two infrared lasers I are symmetrically arranged on both sides of the infrared thermal imager, their heights are the same, and the angles with the horizontal plane are the same. The lenses of the two infrared lasers I are symmetrically arranged and the defocused light spots of the two coincide on the circuit board to be tested directly below the infrared thermal imager; the powers and pulse durations of the two infrared lasers I are kept consistent.

[0012] As a preferred example, the heat source is a flat infrared spotlight, and its light irradiates vertically downward.

[0013] As a preferred example, the heat source is a DLP type infrared laser loading source, the DLP type infrared laser loading source comprises an infrared laser II, a DLP control circuit board and a focusing lens, the DLP control circuit board comprises a DMD chip, the infrared laser II irradiates on the DMD chip, and the reflected projection image passes through the focusing lens and irradiates on the circuit board to be tested and coincides with each component in the circuit board to be tested. The projection image is a gray level diagram of the graphics of each component drawn according to the different absorption rates of infrared light by different components in the circuit board to be tested. For components with different absorption rates of infrared light from large to small, the gray level of the component graphics gradually transitions from gray to white.

[0014] Further, set the projection image corresponding to the component with a metal coating on the surface to white, and set the projection image corresponding to the component with a black plastic package on the surface to gray.

[0015] A screening method using the infrared rapid screening system described above includes the following steps:

[0016] Step 1: Use a heat source to heat the whole or a part of the circuit board to be tested. While stopping the heating, the infrared thermal imager takes a thermal image of the whole or a part of the circuit board to be tested that has been heated; when using a heat source to heat the circuit board to be tested, it is necessary to ensure that the temperature of each component rises by 10 - 20 °C within several seconds, and the temperature of no component exceeds 100 °C.

[0017] Step 2: In the thermal image of the circuit board to be tested, if the temperature of the whole or a part of a certain component is higher than the set value compared to the corresponding component in the thermal image of the standard qualified sample board, then there is a solder joint void or defect in this component.

[0018] As a preferred example, the heat source is a DLP - type infrared laser loading source. Adjust the distance and focal length between the DLP - type infrared laser loading source and the circuit board to be tested to make the projection image coincide with each component on the circuit board to be tested. Start the DLP - type infrared laser loading source in the full - power state, irradiate the circuit board to be tested for several seconds, and after stopping the irradiation, use the infrared thermal imager to take a thermal image of the circuit board to be tested.

[0019] As a preferred example, the heat source is a flat - type infrared spotlight. After heating the circuit board to be tested located directly below, use the infrared thermal imager to take a thermal image of the circuit board to be tested.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] The present invention has completely broken through the industry problem of detecting solder joint voids in components of high - density packaged circuit boards. The components that can be detected cover various existing chips and resistor - capacitor components. At the same time, its high efficiency helps to apply the present invention to the production line. For example, for a mobile phone circuit board, it only needs to be irradiated on both the front and back sides once to complete the detection of solder joint voids. Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of the infrared rapid screening system described in the first specific embodiment;

[0023] Figure 2 It is a schematic structural diagram of the circuit board to be tested. a1 and a2 are both BGA chips, b1, b2, b3, b4, d1, d2, d3, d4, and d5 are all resistor - capacitor components; c1 is a QFP / PFP - type chip;

[0024] Figure 3 It is a thermogram of a standard qualified sample. Both a1 and a2 are qualified BGA chips, and b1, b2, b3, b4, d1, d2, d3, d4, and d5 are all qualified resistor-capacitor components; c1 is a qualified QFP / PFP chip; in the temperature scale on the right, light color represents low temperature and dark color represents high temperature;

[0025] Figure 4 It is a thermogram of a circuit board with solder joint voids. a1 is a qualified BGA chip, a2 is a BGA chip with solder joint voids, b1, b2, b4, d2, d3, d4, and d5 are all qualified resistor-capacitor components, and b3 and d1 are resistor-capacitor components with solder joint voids; c1 is a QFP / PFP chip with solder joint voids; in the temperature scale on the right, light color represents low temperature and dark color represents high temperature;

[0026] Figure 5 It is a thermogram of a circuit board with solder joint voids after PS image processing. a2 is a BGA chip with solder joint voids, b3 and d1 are resistor-capacitor components with solder joint voids; c1 is a QFP / PFP chip with solder joint voids; in the temperature scale on the right, light color represents low temperature and dark color represents high temperature;

[0027] Figure 6 It is a schematic diagram of the infrared rapid screening system described in the third specific implementation manner;

[0028] Figure 7 It is a schematic diagram of the infrared rapid screening system described in the fifth specific implementation manner;

[0029] Figure 8 It is the front side photo of a high-density packaged circuit board. A1, A2, A3, and A4 are chips with metal coatings on the surface, and B1 and B2 are black plastic-encapsulated chips;

[0030] Figure 9 It is Figure 8 The back side photo of the high-density packaged circuit board shown;

[0031] Figure 10 It is Figure 8 The grayscale image of the high-density packaged circuit board shown;

[0032] Figure 11 It is a schematic diagram of a conventional projector in the prior art;

[0033] Figure 12 It is a projection schematic diagram of a DLP type infrared laser loading source.

[0034] In the figure, 1 is an infrared thermal imager, 2 is a circuit board to be tested, 3 is a circuit board transport mechanism, 4 is an infrared laser I, 5 is a flat infrared spotlight, 6 is a DLP infrared laser loading source, 7 is a projection image, 8 is the irradiation area of the laser spot, 9 is the irradiation area of the infrared spotlight, 61 is an infrared laser II, 62 is a DLP control circuit board, 63 is a focusing lens, 64 is a DMD chip, and 65 is a beam expander lens. Specific embodiments

[0035] The technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] The present invention is an infrared rapid screening system and screening method for solder joint voids in high-density packaged circuit boards based on the theory of infrared heat conduction. It uses a radiation heat source to quickly heat a surface of part or the whole circuit board, captures the thermal image of the circuit board at the moment when the heat source stops, and compares it with the thermal image obtained under the same conditions of a standard qualified sample, so as to know which component on the circuit board has solder joint voids. The principle is that components with good solder joints can be regarded as good conductors of heat, and most of the heat is conducted to the circuit board while the heat source is heating up, and the absolute value of its temperature rise is not high. For example, it is assumed that component A with good solder joints rises from room temperature to 45°C after being irradiated by a laser with a fixed power for n seconds; when there are solder joint voids in component A, the thermal resistance increases, and only a small part of the heat can be conducted to the circuit board. Similarly, after being irradiated by the laser for n seconds, its temperature rise will reach 65°C. Based on this principle, the present invention can effectively detect and determine that a certain component on this type of circuit board has solder joint voids. Specific embodiment 1

[0038] An infrared rapid screening system for solder joint voids in high-density packaged circuit boards includes an infrared thermal imager 1 and a heat source; the infrared thermal imager 1 is arranged at the focusing height directly above the circuit board 2 to be tested, and the lens faces the circuit board 2 to be tested, and the heat source is located beside the infrared thermal imager 1 for uniformly heating the whole or part of the circuit board 2 to be tested.

[0039] Furthermore, the screening system further includes a circuit board transport mechanism 3, the circuit board transport mechanism 3 is arranged below the infrared thermal imager 1 and the heat source, and a plurality of circuit boards 2 to be tested are evenly placed on the circuit board transport mechanism 3 and pass through the heat source and the infrared thermal imager 1 in sequence.

[0040] Further, the heat source is two infrared lasers I4, which are symmetrically arranged on both sides of the infrared thermal imager 1, with the same height and the same angle with the horizontal plane. The laser central axes emitted by the two infrared lasers I4 are located in the same plane. The lenses of the two infrared lasers I4 are symmetrically arranged and their defocused light spots coincide on the circuit board 2 to be measured directly below the infrared thermal imager 1.

[0041] Further, the powers and pulse durations of the two infrared lasers I4 are kept consistent, so as to ensure that the brightness of the irradiation area 8 of the laser light spot is uniform. Specific Embodiment 2

[0043] A rapid screening method using the infrared rapid screening system for solder joint voids in high-density packaged circuit boards described in Specific Embodiment 1 includes the following steps:

[0044] Step 1: Place the circuit board 2 to be measured on the circuit board transportation mechanism 3. The schematic structural diagram of the circuit board to be measured is as shown in Figure 2 Shown. Operate the circuit board transportation mechanism 3 to make the circuit board 2 to be measured within the field of view of the infrared thermal imager 1 and also within the irradiation area 8 of the infrared laser light spot, as shown in Figure 1 Shown. Start the two infrared lasers I4. First, adjust the powers and irradiation times of the two infrared lasers I4, and gradually experiment from small to large to ensure that the temperatures of all components within the field of view of the infrared thermal imager 1 increase by 10 - 20 °C within a few seconds, so as to ensure sufficient resolution of the void soldering degree, and the temperature of no component exceeds 100 °C to avoid damaging the components. Select n watts and m seconds as the detection parameters within this range. The two infrared lasers I4 uniformly heat the whole or part of the circuit board 2 to be measured. When the heating stops, start the infrared thermal imager 1 to take a thermal image of the whole or part of the circuit board 2 to be measured that has been heated. Repeat the above steps to detect and photograph multiple similar circuit boards. If the thermal images are consistent and the electrical tests are normal, then it can be confirmed that this thermal image is the standard qualified template thermal image of this type of circuit board; see Figure 1 . If there are any abnormalities, they are screened out, and then increase the number of sample circuit boards until a standard qualified template image is obtained; Figure 3 .

[0045] Step 2: When a thermal image as shown in Figure 4 is found during actual detection, in the thermal image of the circuit board 2 to be measured, there is a high-temperature point in the whole or part of a certain component, and it is much higher than the corresponding component in the control standard qualified template image, which indicates that there may be solder joint voids or defects in this component. Use PS or other software to perform a subtraction process on the obtained Figure 4 and Figure 3 thermal images, and Figure 5The shown thermogram can quickly and conveniently find the abnormal points; according to the temperature scale in the infrared thermal imager 1, the difference between these abnormal points and the standard value can be compared, and the larger the difference, the greater the defect; generally, the error tolerance of resistance-capacitance components is between 2-5 °C. When the difference between the highest temperature of a certain component of this type and the standard value > 5 °C, it can be judged that there is a solder joint with a loose solder; for chip components, mainly check whether there are local abnormal hot spots, and the loose solder joint is located under the hot spot position. Specific Embodiment Three

[0047] An infrared rapid screening system for loose solder joints of high-density packaged circuit boards includes an infrared thermal imager 1 and a heat source; the infrared thermal imager 1 is arranged directly above the circuit board 2 to be tested and the lens faces the circuit board 2 to be tested, and the heat source is located beside the infrared thermal imager 1 for uniformly heating the whole or part of the circuit board 2 to be tested.

[0048] Further, the screening system further includes a circuit board transportation mechanism 3. The circuit board transportation mechanism 3 is arranged below the infrared thermal imager 1 and the heat source. A plurality of circuit boards 2 to be tested are evenly placed on the circuit board transportation mechanism 3 and pass through the heat source and the infrared thermal imager 1 in sequence.

[0049] Further, the heat source is a flat infrared spotlight 5, and its light irradiates vertically downward. Specific Embodiment Four

[0051] A screening method using the infrared rapid screening system for loose solder joints of high-density packaged circuit boards described in Specific Embodiment Three includes the following steps:

[0052] Step 1: Place the circuit board 2 to be tested on the circuit board transportation mechanism 3, operate the circuit board transportation mechanism 3 to run so that the circuit board 2 to be tested is located in the infrared spotlight irradiation area 9 below the flat infrared spotlight 5, irradiate the whole or part of the circuit board 2 to be tested with x watts for y seconds, and then the circuit board transmission mechanism 3 quickly moves it into the field of view of the infrared thermal imager 1; the infrared thermal imager 1 takes a picture of the whole or part of the heated circuit board 2 to be tested to obtain a thermogram; repeat the above steps to detect and take pictures of multiple similar circuit boards. If the thermograms are consistent and the electrical tests are normal, then it can be confirmed that this thermogram is the standard qualified template image of this type of circuit board. If there are abnormalities, they are screened out, and then the number of sample circuit boards is increased until the standard qualified template image is obtained; Figure 1 Before actual detection, first adjust the power and irradiation time of the flat infrared spotlight 5, gradually experiment from small to large, ensure that the temperature of each component rises by 10-20 °C within a few seconds, so as to ensure sufficient resolution of the loose solder degree, and the temperature of no component exceeds 100 °C to avoid damaging the components. Select x watts and y seconds as the detection parameters within this range;

[0053]

[0054] ​Step 2: The same as Step 2 in Specific Embodiment 2. Specific Embodiment 5

[0056] In Specific Embodiment 1 and Specific Embodiment 3, the heating method of uniform light illumination is adopted. However, the components on the circuit board are very different, and their absorption rates of infrared light are also different. Sometimes, the component a with a high absorption rate in the field of view has reached 100 °C, while the component b with a low absorption rate is only 30 °C (the resolution of the soldering degree is relatively low, taking the room temperature of 24 °C as an example).

[0057] For this reason, an ideal infrared laser loading source should treat them differently, that is, use low-power infrared light to irradiate the component a with a high absorption rate and high-power infrared light to irradiate the component b with a low absorption rate within the same heating time. In this way, after irradiating with infrared light for n seconds, the temperature rises of both components a and b are within an ideal detection required range.

[0058] The infrared rapid screening system described in this specific embodiment can be understood as a black and white projector, except that the projection lamp in the machine is replaced with an infrared laser II 61, and the condensing lens and color filter are removed, as Figure 11 and 12 shown. Its advantage is that it can selectively heat different components on the circuit board to be tested graphically. The specific solution is as follows: An infrared rapid screening system for solder joint voids in a high-density packaged circuit board includes an infrared thermal imager 1 and a heat source; the infrared thermal imager 1 is arranged directly above the circuit board to be tested and the lens faces the circuit board to be tested, and the heat source is located beside the infrared thermal imager 1 for heating the whole or part of the circuit board to be tested.

[0059] Furthermore, the screening system further includes a circuit board transportation mechanism 3. The circuit board transportation mechanism 3 is arranged below the infrared thermal imager 1 and the heat source, and several circuit boards to be tested are evenly placed on the circuit board transportation mechanism 3 and pass through the heat source and the infrared thermal imager 1 in sequence.

[0060] Furthermore, the heat source is a DLP - type infrared laser loading source 6. The DLP - type infrared laser loading source 6 includes an infrared laser II 61, a DLP control circuit board 62, and a focusing lens 63. The DLP control circuit board 63 includes a DMD chip 64. Here, the DMD chip 64 is equivalent to a mirror display. Controlled by a computer, it displays the pictures in the computer. The infrared laser II 61 irradiates on the DMD chip 64, and the reflected projection image 7 is irradiated onto the circuit board to be tested 2 through the focusing lens 63 for the sub - area heating of the circuit board to be tested 2. The projection image 7 of the DLP - type infrared laser loading source 6 coincides with each component in the circuit board to be tested 2. The projection image 7 is a gray - scale level diagram (i.e., a gray - scale image) of the graphics of each component drawn according to the different absorption rates of infrared light by different components in the circuit board to be tested 2. For the components with different absorption rates of infrared light from large to small, the gray - scale level of the component graphics gradually transitions from gray to white. The principle of the DMD chip 64 reflecting the projection image 7 is as follows: In the area of the DMD chip 64 corresponding to the white part in the gray - scale image, the mirror is stationary, and the infrared laser is totally reflected to the focusing lens 63; in the area of the DMD chip 64 corresponding to the gray part in the gray - scale image, the mirror deflects back and forth at a certain frequency. When deflecting, part of the laser is reflected out and does not pass through the focusing lens 63 for projection, so part of the laser is wasted. In this way, less laser is reflected through the focusing lens 63, showing a certain gray - scale; in the area of the DMD chip 64 corresponding to the pure - black part in the gray - scale image, the mirror is controlled to be always in the deflected position and is reflected elsewhere without passing through the focusing lens 63.

[0061] Preferably, the DLP - type infrared laser loading source 6 further includes a beam - expanding lens 65. The beam - expanding lens 65 is arranged between the infrared laser II 61 and the DMD chip 64, and the light of the infrared laser II 61 irradiates onto the DMD chip through the beam - expanding lens 65.

[0062] Furthermore, the projection image 7 corresponding to the component with a metal coating on the surface is set to white, and the projection image 7 corresponding to the component with a black plastic package on the surface is set to gray. Specific Embodiment Six

[0064] A screening method using the infrared rapid screening system for solder joint voids in high - density packaged circuit boards described in Specific Embodiment Five includes the following steps:

[0065] Step 1: Directly take a photo of the circuit board 2 to be tested before detection and upload the photo to the control computer of the DLP infrared laser loading source 6; on the computer, design and modify the gray levels of the patterns of each component according to the different absorption rates of the components on the circuit board 2 to be tested. For example, set a chip with a metal coating on its surface (low absorption rate) to white (equivalent to full power irradiation); set a black plastic encapsulated chip (high absorption rate) to gray (equivalent to half power irradiation). In this way, it can be ensured that after the two chips are irradiated by infrared laser for n seconds, on the one hand, the chip with a metal coating (low absorption rate) has sufficient temperature rise, and on the other hand, the black plastic encapsulated chip (high absorption rate) will not overheat;

[0066] Adjust the distance and focal length between the DLP infrared laser loading source 6 and the circuit board 2 to be tested so that the projection image 7 coincides with each component on the circuit board 2 to be tested. Start the DLP infrared laser loading source 6 in the full power state and irradiate the circuit board 2 to be tested for several seconds, generally between 3 - 10 seconds. After stopping the irradiation, control the circuit board transmission mechanism 3 to move quickly (generally within 1 second) to under the fixed field of view of the infrared thermal imager 1, and use the infrared thermal imager 1 to take a photo of the circuit board 2 to be tested to obtain a thermal image; Repeat the above steps to detect and photograph multiple similar circuit boards. If the thermal images are consistent and the electrical tests are normal, then it can be confirmed that this thermal image is the standard qualified template image of this type of circuit board. If there are abnormalities, they are screened out, and then the number of sample circuit boards is increased until the standard qualified template image is obtained; Figure 1 Step 2: Compare this thermal image with the standard template to determine whether there are solder joint defects on this circuit board and which component it is. The steps are the same as those in Step 2 of the second specific implementation method.

[0067] Specific implementation method seven For high - density packaged circuit boards in a situation similar to that shown in the figure, taking 6 chips as an example: in the circuit board to be tested, A1, A2, A3, and A4 are chips with metal coatings on their surfaces, and B1 and B2 are black plastic encapsulated chips. It is desired to irradiate the chips A1, A2, A3, and A4 with full power for heating, and use low - power irradiation for the chips B1 and B2. Then the infrared laser to be irradiated is as shown in the figure. The gray levels of the positions corresponding to the chips A1, A2, A3, and A4 are set to white, and the gray levels of the positions corresponding to the chips B1 and B2 are set to gray. According to the physical photo, it is very convenient to process such a gray - scale image with different gray levels using photo - processing software on the computer, and use it as the projection image 7. Open this picture on the control computer of the DLP infrared laser loading source, adjust the focal length and distance, and then the projection image 7 can be projected onto

[0069] The present invention aims at high - density packaged circuit boards in a situation similar to that Figure 8 shown. Taking 6 chips as an example: in the circuit board to be tested, A1, A2, A3, and A4 are chips with metal coatings on their surfaces, and B1 and B2 are black plastic encapsulated chips. It is desired to irradiate the chips A1, A2, A3, and A4 with full power for heating, and use low - power irradiation for the chips B1 and B2. Then the infrared laser to be irradiated is as shown in the figure. The gray levels of the positions corresponding to the chips A1, A2, A3, and A4 are set to white, and the gray levels of the positions corresponding to the chips B1 and B2 are set to gray. According to the physical photo, it is very convenient to process such a gray - scale image with different gray levels using photo - processing software on the computer, and use it as the projection image 7. Open this picture on the control computer of the DLP infrared laser loading source, adjust the focal length and distance, and then the projection image 7 can be projected onto Figure 10 shown. The gray levels of the positions corresponding to the chips A1, A2, A3, and A4 are set to white, and the gray levels of the positions corresponding to the chips B1 and B2 are set to gray. According to the physical photo, it is very convenient to process such a gray - scale image with different gray levels using photo - processing software on the computer, and use it as the projection image 7. Open this picture on the control computer of the DLP infrared laser loading source, adjust the focal length and distance, and then the projection image 7 can be projected onto Figure 8On the circuit board to be measured as shown, each area coincides with the chips A1, A2, A3, A4, B1, and B2 one by one. In this way, the four chips A1, A2, A3, and A4 are heated by full-power irradiation (white), and the two chips B1 and B2 are heated by low-power irradiation (dark gray). After the infrared laser II 61 is turned on and irradiated for n seconds, the temperatures of these 6 chips all rise to 70 °C. If a DLP-type infrared laser loading source is not used and the ordinary infrared laser with a uniform light spot is used to heat for n seconds, the four chips A1, A2, A3, and A4 also reach 70 °C, but at the same time, the two chips B1 and B2 may reach 200 °C (the solder joints in the chips will melt). Therefore, if only a simple infrared laser is used, the power of the above chips needs to be set one by one, and only one-by-one detection can be performed, resulting in low efficiency. In the present invention, in the case where the projection image 7 is set, the DLP-type infrared laser loading source can detect an entire surface of the circuit board at one time without considering the types of chips and resistor-capacitor components on the circuit board. The task can be completed by detecting the front and back sides of a circuit board once respectively, enabling efficient screening and keeping up with the assembly line rhythm. When detecting different circuit boards, only the projection image 7 needs to be replaced, and the method is the same as above, with flexible application.

[0070] Figure 11 Fig. shows the schematic diagram of a conventional projector in the prior art; Figure 12 Fig. shows the projection schematic diagram of the DLP-type infrared laser loading source described in the present invention.

[0071] In the figure, the DMD chip is equivalent to a mirror display, and can display any image at will under the control of a computer (the grayscale image of the circuit board 2 to be measured is displayed in the present invention). The infrared laser irradiates on it, and then after reflection, the projection image 7 is projected onto the circuit board 2 to be measured through the focusing lens 63.

[0072] In addition, it should be understood that although this specification is described according to the embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A screening method for infrared rapid screening of solder joint voids in high-density packaging circuit boards, characterized in that: The infrared rapid screening system for solder joint voids in high-density packaging circuit boards includes an infrared thermal imager (1) and a heat source; the infrared thermal imager (1) is arranged directly above the circuit board to be tested (2) with the lens facing the circuit board to be tested (2), and the heat source is located beside the infrared thermal imager (1) for heating the whole or part of the circuit board to be tested (2). The screening method includes the following steps: Step 1: Use the heat source to heat the whole or part of the circuit board to be tested (2). At the same time as stopping the heating, the infrared thermal imager (1) takes a thermal image of the whole or part of the heated circuit board to be tested (2). When using the heat source to heat the circuit board to be tested (2), it is necessary to ensure that the temperature of each component rises by 10 - 20 °C within a few seconds, and the temperature of no component exceeds 100 °C. Select x watts and y seconds as the detection parameters within this range. Step 2: In the thermal image of the circuit board to be tested (2), if the temperature of the whole or part of a certain component is higher than the set value compared to the corresponding component in the thermal image of the standard qualified sample board, then there is a solder joint void or defect in this component. The heat source is a DLP - type infrared laser loading source (6). The DLP - type infrared laser loading source (6) includes an infrared laser II (61), a DLP control circuit board (62), and a focusing lens (63). The DLP control circuit board (62) includes a DMD chip (64). The infrared laser II (61) irradiates on the DMD chip (64), and the reflected projection image (7) passes through the focusing lens (63) and irradiates on the circuit board to be tested (2) and coincides with each component in the circuit board to be tested (2). The projection image (7) is a gray - scale level diagram of the graphics of each component drawn according to the different absorption rates of infrared light by different components in the circuit board to be tested (2). For components with decreasing absorption rates of infrared light from large to small, the gray - scale level of the component graphics gradually transitions from gray to white.

2. The screening method according to claim 1, wherein: The screening system further includes a circuit board transportation mechanism (3). The circuit board transportation mechanism (3) is arranged below the infrared thermal imager (1) and the heat source. Several circuit boards to be tested (2) are evenly placed on the circuit board transportation mechanism (3) and pass through the heat source and the infrared thermal imager (1) in sequence.

3. The screening method according to claim 1, wherein: Set the projection image (7) corresponding to the component with a metal coating on the surface to white, and set the projection image (7) corresponding to the component with a black plastic package on the surface to gray.

4. The screening method according to claim 1, wherein: The heat source is a DLP - type infrared laser loading source (6). Adjust the distance and focal length between the DLP - type infrared laser loading source (6) and the circuit board to be tested (2) so that the projection image (7) coincides with each component on the circuit board to be tested (2). Start the DLP - type infrared laser loading source (6) in the full - power state and irradiate the circuit board to be tested (2) for several seconds. After stopping the irradiation, use the infrared thermal imager (1) to take a thermal image of the circuit board to be tested (2).

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