CN114878603A - BGA chip cold joint detection method and detection system - Google Patents

Abstract

The invention provides a BGA chip rosin joint detection method and a detection system, wherein a circuit board welded with the BGA chip is positioned on a high-temperature vibration assembly; detecting whether the solder joints are in cold joint or not by adopting infrared thermal image data, wherein the solder joints are connected with the via holes or provided with test points; and detecting other welding points by adopting an X-ray image. According to the invention, different detection modes are adopted to carry out the false soldering detection and verification on the BGA welding points of different types and different positions in the circuit board welded with the BGA chip, so that the false detection and the omission of the BGA welding points are avoided, and the efficiency, the accuracy and the pertinence of the false soldering detection of the BGA chip are improved.

Description

BGA chip cold joint detection method and detection system

Technical Field

The invention relates to the field of welding detection, in particular to a BGA chip cold joint detection method and a detection system.

Background

The BGA device is a ball grid array device, the specific morphology is shown in figure 5, the packaging density of the printed board can be greatly improved during the packaging period of the type, and the BGA device is more and more widely applied. Several BGA devices are commonly used including PBGA, CBGA, TBGA, etc. With the continuous development of BGA devices, micro-BGAs such as μ BGA and CSP have been developed and applied, and have a package size of 20% larger than the chip size, a minimum solder ball size of 0.3mm, and a minimum solder ball pitch of 0.5 mm. With the development of light and small electronic products, BGA packaged chips are widely used in surface mount technology as a new high-density packaging technology. The main advantages of electronic chip BGA packages are: (1) the packaging occupied area is small; (2) the number of pins is large, and the interface function is richer; (3) the automatic mounting is realized, and the efficiency is higher; (4) the whole production cost is low. The BGA package still has the following problems: (1) because the BGA welding spot is hidden at the bottom of the chip, the BGA welding spot cannot be directly detected after welding and assembling, and other detection methods have higher cost; (2) the welding spot has small area and low mechanical strength and is easy to break under the action of stress; (3) the thermal expansion mismatch between the component and the substrate during heating can cause the chip to bend, even the solder joint cracks and other problems.

And the quality and reliability of the PCB are directly related to those of the electronic products. Solder joint cold joint is a common problem in the production process of the PCB, and the factors for generating the solder joint cold joint are very complex and cannot be removed from the production process. Therefore, the detection of the cold solder joint is crucial. Currently, there are three main detection methods applied in the industry: automatic Optical Inspection (AOI), automatic X-ray inspection (AXI), and flying probe testing. The detection technologies have advantages and disadvantages and complement each other, but even if the three technologies are comprehensively utilized, the defects of the welding spots cannot be ensured to be detected. For example, some welding spots such as cold welding, poor local wetting, greasy dirt oxidation and the like have normal appearance and electrical connection, and the detection of the welding spots is a worldwide problem at present.

For the bonding of the BGA packaged chip, the manufacturer usually uses visual observation to see whether the collapse of the outermost ring of pads is consistent, and then looks at the chip with respect to the light, if each row and each column can transmit light, it can be preliminarily determined that there is no bridging and some solder balls with larger size can be seen. However, it is difficult to determine whether a solder joint is defective in this manner because it is not possible or difficult to determine whether the solder joint therein has other defects or whether there are voids in the solder joint. In order to detect the inherent defects of the BGA package device or more accurately detect the quality of the welding spots without damaging the structure, performance and the like of the BGA package device, other more advanced and reliable nondestructive detection methods are required. For the surface assembly welding spot, common nondestructive detection methods include X-ray detection, three-dimensional optical camera inspection, laser infrared detection, ultrasonic detection and other methods, flying probe electronic test, X-ray detection, dyeing detection and section detection. The dyeing and slicing detection is destructive detection, can be used as a failure analysis means, and is not suitable for welding quality detection. In the nondestructive testing, visual inspection can only detect the solder balls at the edges of the device, but cannot detect the internal defects of the solder balls; the misjudgment rate of the flying probe electronic test is too high; the X-ray detection utilizes the X-ray transmission characteristic, can well detect the welding condition of the solder balls hidden under the device, and is the most effective BGA welding quality detection method at present. However, the X-ray is only limited to detect the limited defects such as continuous welding, cavities and the like at present and can not cover all BGA welding defects; and lack of detection standards. Moreover, the above-mentioned various detection methods cannot accurately detect whether the BGA has a faulty solder or not, and problems such as a false detection or a missing detection exist are to be solved.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention provides a BGA chip cold solder joint detection method, which comprises the following steps:

positioning the circuit board after the BGA chip is welded on the high-temperature vibration assembly;

detecting whether the cold joint exists or not by adopting infrared thermal image data for the welding spots connected with the via holes or provided with the test points;

and performing cold joint detection on other welding points by adopting an X-ray image.

Optionally, the detecting whether the cold joint exists by using the infrared thermal image data specifically includes the following steps:

thermally exciting the via hole or the test point by using a pulse heat source, collecting surface temperature change of the welding point under thermal excitation by using infrared thermal imaging equipment to obtain a residual temperature time curve, and performing cross-correlation operation on the curve and the residual temperature time curve of a normal welding point to obtain a cross-correlation coefficient;

and if the cross correlation coefficient is larger than or equal to the cross correlation threshold value, judging that the welding spot is normal, otherwise, judging that the welding spot is insufficient welded.

Optionally, the step of performing cold joint detection on the other welding spots by using the X-ray image specifically includes the following steps:

for the welding spots to be detected with the welding spots all around, comparing the pixel area of the welding spots to be detected with the average value of the pixel areas of other 8 welding spots around, and if the area difference value is within the difference value range, judging that the welding spots to be detected are normal; otherwise, judging that the solder joint to be tested possibly has cold solder joint and needing further verification;

and for the welding spot to be detected at the edge of the device, judging whether the welding spot to be detected has dark ring, if so, judging that the welding is good, otherwise, judging that the welding spot to be detected is possible to be in cold joint, and needing further verification.

Optionally, for the solder joint to be tested that needs to be further verified, the following steps are further provided:

obtaining the coordinates of the mass centers of other welding points in the same column with the welding point to be verified according to the X-ray image, fitting out a column straight line L1 according to the coordinates of the mass centers, and calculating the vertical distance D1 between the mass center of the welding point to be verified and the column straight line;

fitting a line L2 according to the coordinates of the centers of mass of other welding points in the same line, and calculating the vertical distance D2 between the center of mass of the welding point to be verified and the line;

and if D1 and D2 are smaller than the distance threshold T1 at the same time, judging that cold joint does not occur, otherwise, judging that cold joint occurs.

Optionally, the following steps are further provided:

detecting the warping of the welding part of the BGA chip in the PCB and the warping of the BGA chip before welding;

and detecting whether holes or bubbles exist in the welding spots of the warping parts, wherein the sum of the areas of the holes or the bubbles exceeds 20% of the diameter of the solder balls, and judging that the welding spots have cold joints.

The invention also provides a BGA chip rosin joint detection system which comprises a warpage detection module, a high-temperature vibration module, an X-ray detection module and an upper computer control and calculation module, wherein the upper computer control and calculation module is electrically connected with and controls the warpage detection module, the high-temperature vibration module and the X-ray detection module, and processes detection data.

The invention has the beneficial effects that:

1. performing cross-correlation operation on the welding spots connected with the through holes and the welding spots provided with the test points by adopting the excess temperature-time curve of the welding spots to be tested and the excess temperature-time curve of the normal welding spots, and judging whether the insufficient welding exists or not by comparing cross-correlation coefficients, wherein the detection efficiency is higher;

2. for the middle welding spot, judging whether the middle welding spot is in a cold joint or not by detecting the difference value between the pixel area of the welding spot to be detected and the average area of the surrounding welding spots, the detection is easy to realize by adopting an image processing mode, and the detection efficiency and the automation degree are improved;

3. for the edge welding spot, whether the welding spot has dark ring or not is detected to judge whether the welding spot is in cold joint or not, and the detection is carried out in a gray gradient change mode, so that the method is simple and effective;

4. judging the distances between the mass center of the welding spot and the line straight line of the welding spot for the welding spot with the normal difference of the average areas and the welding spot with the dark ring, realizing confirmation of the false welding of the welding spot and avoiding error detection;

5. the warping part is subjected to key detection, so that missing detection is avoided, and the pertinence and the effectiveness of the insufficient solder detection are improved;

6. the method has the advantages that a targeted detection method is provided for different types of welding spots and welding spots at different positions, so that the detection efficiency and the detection pertinence are improved, and meanwhile, the detection efficiency is improved;

7. the circuit board welded by the BGA chip is vibrated at high temperature, so that the welding problem is more easily exposed, the problem detection rate is improved, and the omission of detection is avoided;

8. set up the vibrations subassembly in high temperature environment to circuit board to different sizes and different grade type, can set up different vibration frequency, with the pertinence that improves solder joint problem screening, improve welding problem exposure rate.

Drawings

FIG. 1 is a schematic view of a solder joint with a significantly unacceptable solder joint area;

FIG. 2 is a schematic diagram showing distances between the centroid of a weld spot and a row line and a column line;

FIG. 3 shows an X-ray scan image of a weld dark ring;

FIG. 4 is a flow chart of the solder joint rosin joint detection method of the BGA chip of the present invention;

FIG. 5 shows a schematic view of the BGA package chip topography.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of the invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, only for the purpose of facilitating description of the present invention and simplifying description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

Example 1

In order to solve the problems that the insufficient solder joint problem of the BGA chip proposed in the background art is difficult to be detected accurately and has false detection or missing detection, the embodiment discloses a method for detecting the insufficient solder joint of the BGA chip, the flow of the detection method is as shown in fig. 4, and the specific implementation steps are as follows:

and step 1, after completing the welding of the BGA chip, fixing the welded circuit board on a vibration assembly for vibration, and arranging the vibration assembly in a high-temperature environment.

Specifically, because when carrying out the rosin joint and detecting, it is errorless often to appear PCB circuit board welding after accomplishing to detect, but because the reason of welding potential problems such as insecure when later stage uses, soldering tin drops probably to appear, and then PCB board welding is bad when causing the rosin joint to detect is detected as qualified, but follow-up in-service erroneous judgement phenomenon that the rate is high, PCB board yields low scheduling problem.

Consequently in order to solve this technical problem, set up vibration subassembly drive in this embodiment and accomplish BGA chip welded PCB board and vibrate, make rosin joint, the weak solder joint of solder joint combination in vibration process, soldering tin and solder joint are changeed and are separated, and then detect through the PCB circuit board to after shaking, can make the PCB board of soldering tin and solder joint separation as the defective products more easily detected out, improve the accuracy of test result, reduce the erroneous judgement rate.

And the high-temperature environment can promote the further exposure of the welding problem, further make defective products more easily detect out, further improve the accuracy of test result, reduce the erroneous judgement rate.

For circuit boards of different sizes and different types, different vibration frequencies are set in the embodiment so as to improve the pertinence of the problem screening of the welding spots.

And 2, detecting whether the solder joints have cold solder joints or not by adopting infrared thermal image data for the BGA solder joints connected with the via holes or the BGA solder joints provided with the test points.

Specifically, during detection, the BGA solder points connected to the via holes or the BGA solder points provided with the test points are selected, and then the corresponding via holes or the test points are thermally excited by using a pulse heat source, which may be a laser, a xenon lamp, or other light-gathering heat sources.

Specifically, the value range of the excitation angle of the pulse heat source is 45-60 degrees, the value range of the excitation time of the pulse heat source is 0.3-0.9 second, the size of a light spot formed by the excitation of the pulse heat source is smaller than 80% of the area of a welding spot, the value range of the surface heating rate of the pulse heat source excitation test object is 15-50 ℃/s, and the excitation angle of the pulse heat source is perpendicular to the surface tangential direction of the test object.

And then, acquiring the surface temperature change of the detected welding spot under thermal excitation by adopting an infrared thermal imaging device to obtain an excess temperature time curve of the detected welding spot, performing cross-correlation operation on the excess temperature time curve of the welding spot and the excess temperature time curve of the normal welding spot to obtain a cross-correlation coefficient between the two curves, and if the cross-correlation coefficient is greater than or equal to a fixed threshold value, judging that the welding spot has no rosin joint and belongs to the normal welding spot. And otherwise, if the obtained cross correlation coefficient is smaller than the fixed threshold value, judging that the cold joint occurs in the welding spot.

And 3, detecting whether the BGA welding spots which are not connected with the via holes and are not provided with the test points by adopting X-rays.

Specifically, X-rays are adopted to scan the welding spots to be detected and the welding spots nearby the welding spots to obtain corresponding X-ray scanning images, an image processing algorithm is adopted to obtain gray level images of the welding spots, and detection in different modes is performed on the basis of the gray level images of the welding spots at different positions.

In a specific case one, for a BGA welding spot to be detected with welding spots arranged on the periphery, comparing the pixel area of the welding spot to be detected with the average value of the pixel areas of the surrounding 8 welding spots, if the area difference value between the welding spot to be detected and the average value of the pixel areas of the surrounding 8 welding spots is within a preset threshold value range, judging that the BGA welding spot is well welded, and ending the detection; on the contrary, if the area difference is outside the threshold range, it indicates that the solder joint may have a cold solder joint, and further confirmation is required.

Referring to fig. 1, the pixel area of the middle solder joint is obviously smaller than the pixel area of the 8 peripheral solder joints, and the pixel area of the middle solder joint is obviously smaller than the average value of the pixel areas of the 8 peripheral solder joints, which indicates that a cold joint may exist in the soldering process of the solder joint, and it is necessary to further confirm whether the cold joint exists in the solder joint subsequently.

Further, more specifically, the inventor finds out through long-term experiments and experiences and data accumulation and summarization that the threshold value is set to be 19%, and the cold solder joint can be detected more accurately.

In a second specific case, different from the detection method for the BGA solder points to be detected with solder points all around, for the solder points located at the edge of the BGA device, it is first determined whether dark bright dark bright dark bright dark bright dark bright dark bright.

Specifically, when the dark ring is determined, the gradient change of the gray scale is calculated from the center of the welding spot along eight directions, and if the gradient change of the gray scale exists and the gradient change of the gray scale in 8 directions is uniform, the dark ring exists. The specific 8 directions are 8 directions of up, down, left, right, left-up, left-down, right-up and right-down.

In order to further improve the detection accuracy, the number of directions in which the gray scale gradient change is detected may be adjusted, for example, one gray scale gradient change is detected every 30 ° in the circumferential direction.

And 4, verifying that the solder joint in the step 3 may exist in the step 3 through the offset of the solder joint because the solder joint of the BGA solder joint generally accompanies the offset of the solder joint, and further confirming whether the solder joint is in the step.

Specifically, as shown in fig. 2, for the welding point that needs to be further confirmed whether there is a cold joint in step 3, in step 4, first, an X-ray scanning image of the welding point in the same column as the welding point to be detected is obtained, the coordinates of the centers of mass of the welding points in the column except the welding point to be detected are calculated, and a column straight line L1 is fitted according to the coordinates of the centers of mass. And then calculating the centroid coordinate of the welding point to be detected, and calculating the vertical distance D1 between the centroid coordinate of the welding point to be detected and the fitted column straight line L1.

Similarly, other welding points in the same row as the welding point to be detected are detected, the centroid coordinates of the other welding points in the row except the welding point to be detected are calculated, and a row straight line L2 is fitted according to the centroid coordinates. And then calculating the centroid coordinate of the welding point to be measured, and calculating the vertical distance D2 between the coordinate of the welding point to be measured and the fitted line L2.

On the basis of obtaining the vertical distance D1 between the welding point to be detected and the column straight line L1 and the vertical distance D2 between the welding point to be detected and the row straight line L2, if D1 and D2 are smaller than a distance threshold T1 at the same time, the condition that the cold welding does not occur is judged, and if not, the condition that the cold welding occurs at the point is judged.

By adopting the BGA chip false soldering detection method, the false soldering point of the BGA chip after being soldered can be accurately detected, missing inspection is avoided, possible false soldering points can be verified in different modes, and false inspection of the false soldering points is avoided.

Example 2

The embodiment is further improved on the basis of embodiment 1, and common parts of the technical solutions are not described herein again.

When the welding part of the BGA chip in the PCB has large warpage, the welding surface is uneven, which may cause that a part of the BGA solder balls cannot be welded well with the bonding pads on the PCB, and a large false soldering risk exists, so that the warpage detection needs to be performed on the welding part of the BGA chip in the PCB before welding, so as to perform the following key detection on the welding quality of the area with large warpage, thereby improving the detection efficiency and pertinence.

For example, if it is detected before soldering that a relatively obvious warpage deformation exists in an upper right corner region in a soldering portion of a BGA chip, the upper right corner region is subjected to an emphasis detection in a subsequent cold solder joint detection, so as to ensure the accuracy and pertinence of the cold solder joint detection and avoid missing detection.

Similarly, the problem of warpage deformation also exists for the BGA chip with a larger size, and the warpage deformation of the BGA chip also may cause that a part of the BGA solder balls cannot be well soldered to the pads on the PCB, so that a larger risk of insufficient soldering exists, and therefore, the warpage deformation of the BGA chip needs to be detected before soldering, so as to perform key detection on the soldering of the region with the larger warpage deformation at the part, and improve the efficiency and pertinence of the detection.

Therefore, in this embodiment, before step 1, step 1.1 is further provided, where step 1.1 is specifically as follows:

step 1.1, before the BGA chip is welded, detecting the warping of the welding part of the BGA chip in the PCB and the warping of the BGA chip, and recording the possible warping part.

Specifically, in this step, during the warpage detection of the PCB or BGA chip, various mature warpage detection methods in the prior art, such as speckle deformation detection, three-dimensional image detection, etc., may be adopted, and the above methods are widely applied in the prior art, and the technology is relatively mature, and therefore, are not described in detail in this embodiment.

Correspondingly, in this embodiment, after step 4, step 5 is further provided, where step 5 is specifically as follows:

step 5, after detecting the PCB part with warpage and the BGA chip part with warpage, performing key detection; according to long-term work experience and objective data of an inventor, the warped part exists, and due to the fact that the gap between the PCB and the BGA chip is not uniform at the part, holes or bubbles are prone to appear in a welding point in the welding process, and therefore on the basis of an X-ray scanning image of the warped part, image processing is conducted, and whether the holes or the bubbles exist in the welding point of the part to be detected or not is judged.

Specifically, edge detection is performed on an image, then expansion and contraction processing of the image is performed, then whether holes or bubbles exist is detected, and the area of the holes or bubbles is calculated. A solder joint is considered to have a cold joint if the sum of the areas of the holes or bubbles in the solder joint exceeds 20% of the diameter of the solder ball.

In the embodiment, by detecting the emphasis of the warping part, whether the cold solder exists in the part where the cold solder easily appears can be detected in a targeted manner, so that the detection efficiency, accuracy and pertinence are improved.

Example 3

The present embodiment is further improved on the basis of embodiment 1 or embodiment 2, and common parts of the technical solutions are not described herein again.

The embodiment also provides a detection system corresponding to the BGA chip cold solder joint detection method, and the system implements the BGA chip cold solder joint detection method in any one of embodiments 1-2. The system comprises a warpage detection module, a high-temperature vibration module, an X-ray detection module and an upper computer control and calculation module, wherein the upper computer control and calculation module is electrically connected with the warpage detection module, the high-temperature vibration module and the X-ray detection module and controls the warpage detection module, the high-temperature vibration module and the X-ray detection module, and meanwhile, calculation and processing of detection data can be realized.

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment. In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit.

Claims (7)

1. A BGA chip cold joint detection method is characterized by comprising the following steps:

positioning the circuit board welded with the BGA chip on a high-temperature vibration assembly;

detecting whether the solder joints connected with the via holes or the solder joints provided with the test points have insufficient solder joints by adopting infrared thermal image data;

and detecting other welding points by adopting an X-ray image.

2. The BGA chip cold joint detection method of claim 1, wherein detecting whether the solder joints have cold joints by using infrared thermographic data specifically comprises the steps of:

the pulse heat source thermally excites the via hole or the test point;

acquiring the surface temperature change of the welding spot under thermal excitation by using infrared thermal imaging equipment to obtain an excess temperature time curve;

performing cross-correlation operation on the curve and an excess temperature time curve of a normal welding spot to obtain a cross-correlation coefficient;

and if the cross correlation coefficient is larger than or equal to the cross correlation threshold value, judging that the welding spot is normal, otherwise, judging that the welding spot is insufficient.

3. The BGA chip cold solder joint detection method of claim 2, wherein the step of using X-ray image to perform cold solder joint detection on other solder joints specifically includes the steps of:

for the welding spots to be detected with the welding spots all around, comparing the pixel area of the welding spots to be detected with the average value of the pixel areas of other 8 welding spots around, and if the area difference value is within a preset difference value range, judging that the welding spots to be detected are normal; otherwise, judging that the solder joint to be tested possibly has cold solder joint and needing further verification;

and for the welding spot to be detected at the edge of the device, judging whether the welding spot to be detected has dark ring, if so, judging that the welding is good, otherwise, judging that the welding spot to be detected is possible to be in cold joint, and needing further verification.

4. The BGA chip cold solder joint detection method of claim 3, further comprising the following steps for the solder joint to be tested to be further verified:

obtaining the coordinates of the mass centers of other welding points in the same column with the welding point to be verified according to the X-ray image, fitting out a column straight line L1 according to the coordinates of the mass centers, and calculating the vertical distance D1 between the coordinates of the mass centers of the welding points to be verified and the column straight line;

fitting a line L2 according to the centroid coordinates of other welding points in the same line, and calculating the vertical distance D2 between the centroid coordinates of the welding point to be verified and the line;

and if D1 and D2 are smaller than the distance threshold value at the same time, judging that the cold joint does not occur, otherwise, judging that the cold joint occurs.

5. The BGA chip cold solder detecting method of claim 4, wherein warpage of a soldering portion of the BGA chip and warpage of the BGA chip in a circuit board are detected before the BGA chip is soldered.

6. The method of claim 5, wherein the solder joint of the warped portion is tested for the presence of voids or bubbles, and the solder joint is determined to be faulty if the total area of the voids or bubbles exceeds 20% of the diameter of the solder ball.

7. A cold joint detection system based on the BGA chip cold joint detection method of any one of claims 1-6, characterized in that the system comprises a warpage detection module, a high temperature vibration module, an X-ray detection module and an upper computer control and calculation module, wherein the upper computer control and calculation module is electrically connected with the warpage detection module, the high temperature vibration module and the X-ray detection module and controls the same and processes detection data.

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