Method for overcoming defect of tombstone standing in vacuum vapor welding

Abstract

The invention discloses a method for overcoming the defect of tombstone erection in vacuum vapor welding, relates to the technical field of electronic component welding, and adopts a mode of controlling the temperature rise rate in a temperature interval corresponding to a soldering flux infiltration area and a solder paste melting area to ensure that the temperature rise rate of the soldering flux infiltration area and the solder paste melting area is not influenced in the welding process. The problems of surface tension imbalance and the like caused by non-synchronous wetting of the two ends and difference of the melting time of the solder paste at the two ends of the chip packaging device are solved, so that the defect of tombstone standing caused by too high temperature rise rate is effectively prevented. Meanwhile, the provided temperature rise rate control method is simple and easy to implement, and high-precision control can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic component welding, in particular to a method for solving the tombstone defect of vacuum vapor phase welding. BACKGROUND

[0002] With the development of lead-free electronic components, most of the components on the market are lead-free components, but the production of special electronic boards requires the use of lead solder. Lead-free components and lead solder have different welding temperatures, which leads to excessive solder void rate of some components after reflow soldering, affecting product reliability. At the same time, with the rapid development of electronic products, high-end complex electronic boards usually contain high heat-melting components such as large CBGA, large CCGA and high-voltage conductive blocks. The traditional hot air reflow soldering process cannot meet the welding requirements. In view of the above problems, some enterprises introduce vacuum vapor phase welding machines, and after adopting the new process, the solder void rate is reduced from more than 25% to less than 10%, and the problems of excessive solder void rate and insufficient welding capacity of high heat-melting components are completely solved. However, the tombstone defect of 0402 packaged components is serious, and more than 70% of electronic boards have tombstone defects of 0402 packaged components. Tombstone (also known as tombstone effect and drawbridge effect) is a common welding defect in SMT patch processing, mainly manifested as the upwarping of one end of a chip component (such as a resistor or a capacitor) after welding, resulting in abnormal circuit function.

[0003] After adopting the new vacuum vapor phase welding process, the problems of excessive solder void rate and insufficient welding capacity of high heat-melting components are completely solved. However, during the welding process, 0402 packaged chip components are prone to tombstone defects, and the process control is difficult.

[0004] With the development of lead-free electronic components and the rapid development of electronic products, more and more electronic boards need to be welded by vacuum vapor phase welding process, so it has good application prospect.

[0005] Therefore, how to provide a method to solve the tombstone defect existing in vacuum vapor phase welding is an urgent technical problem for those skilled in the art. SUMMARY

[0006] In view of the above problems, the present application provides a method for solving the tombstone defect of vacuum vapor phase welding to overcome the above problems or at least partially solve the above problems.

[0007] The present application provides the following solutions:

[0008] A method for solving the tombstone defect of vacuum vapor phase welding, comprising:

[0009] The target method controls the temperature rising rate in the temperature range corresponding to the solder flux infiltration area and the solder paste melting area in the lead-free mixed soldering temperature curve to be not greater than 0.4℃ per second.

[0010] Wherein, the solder paste in the solder paste infiltration area is on the verge of melting, and the solder paste in the solder paste melting area is in the transition from paste state to liquid state.

[0011] Preferably, the temperature interval comprises 170℃-190℃.

[0012] Preferably, the target method comprises adjusting the temperature rising rate by adjusting the number of layers in which the workpiece stays in the cavity.

[0013] Preferably, the target method comprises adjusting the temperature rising rate by adjusting the bottom heating power.

[0014] According to the specific embodiments provided by the present application, the following technical effects are disclosed:

[0015] The method for solving the monument defect of vacuum vapor phase welding provided by the embodiment of the present application adopts the mode of controlling the temperature rising rate in the temperature interval corresponding to the solder paste infiltration area and the solder paste melting area, so that the chip-type packaging device will not appear the problems such as the different wetting of two ends out of synchronization and the surface tension imbalance caused by the difference in the tin paste melting time of two ends in the welding process, thereby effectively preventing the monument defect caused by the too fast temperature rising rate. At the same time, the temperature rising rate control method is simple and easy to implement and can be controlled with high precision.

[0016] Of course, implementing any product of the present application does not necessarily need to achieve all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0018] Figure 1 is a typical lead-free mixed soldering temperature curve provided by the embodiment of the present application;

[0019] Figure 2 is an internal structure schematic diagram of IBL VAC745 vacuum vapor phase welding machine provided by the embodiment of the present application;

[0020] Figure 3 is a temperature rising rate curve diagram of each layer with a heating power of 60% provided by the embodiment of the present application;

[0021] Figure 4 is a temperature rising rate curve diagram of the 7th and 8th layers with different bottom heating powers provided by the embodiment of the present application. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application shall fall within the scope of the present application.

[0023] The embodiments of the present application provide a method for solving the monument defect in vacuum vapor phase welding, which can comprise:

[0024] The temperature in the temperature interval corresponding to the solder flux infiltration area and the solder paste melting area in the lead-containing and lead-free mixed soldering temperature curve is controlled by the target method, and the temperature rising rate is not greater than 0.4℃ per second.

[0025] The solder paste under the solder flux infiltration area is at the eve of melting, and the solder paste under the solder flux melting area changes from a paste state to a liquid state.

[0026] The method for solving the monument defect in vacuum vapor phase welding provided by the embodiments of the present application controls the temperature rising rate in the temperature interval corresponding to the solder flux infiltration area and the solder paste melting area, prevents the solder flux infiltration area from rising too fast, greatly reduces the probability that the two ends of the component are not wetted synchronously, and enables the two ends of the component to be completely wetted before entering the solder paste melting area, thereby reducing the probability of occurrence of the monument defect. At the same time, the temperature rising rate in the solder paste melting area can be prevented from being too fast, the solder paste melting time at the two ends of the component can be different, the surface tension is unbalanced, and the occurrence of the monument defect of the component is prevented.

[0027] In actual application, the temperature interval can be determined according to the temperature curve obtained by welding different components. For example, in one implementation, the embodiments of the present application can provide that the temperature interval comprises 170℃-190℃.

[0028] It can be understood that the target control method provided by the present application can comprise multiple methods. For example, in one implementation, the embodiments of the present application can provide that the target method comprises adjusting the temperature rising rate by moving the number of layers of the workpiece staying in the cavity.

[0029] In another implementation, the embodiments of the present application can provide that the target method comprises adjusting the temperature rising rate by adjusting the bottom heating power.

[0030] In actual use, any one of the above methods can be used for temperature adjustment, or two methods can be combined for temperature adjustment, so that the temperature rising rate in the two intervals is not greater than 0.4℃ per second.

[0031] The method provided by the present application will be described in detail below.

[0032] After adopting the new process of vacuum vapor phase welding, the problem of excessive cavity rate and the problem of insufficient welding capacity of high heat melting devices are completely solved, but during the welding process, the 0402 packaged chip device is prone to standing monument defects, and the process control is difficult.

[0033] The present application proposes a new process method, which analyzes the serious problem of standing monument defect in vacuum vapor phase welding in depth, locates the fault cause, and then collects and compares the influence degree of different process parameters on standing monument defect through process verification, to obtain the process method for solving the serious problem of standing monument defect in vacuum vapor phase welding.

[0034] 1. Analyze the cause of standing monument defect in vacuum vapor phase welding process.

[0035] As shown in Figure 1 , the typical lead-free mixed soldering temperature curve mainly includes the heating zone, the holding zone, the flux infiltration zone, the solder paste melting zone, the vapor phase welding zone and the cooling zone, wherein the temperature rising rate of the flux infiltration zone and the solder paste melting zone is the factor affecting the standing monument defect.

[0036] The temperature of the flux infiltration zone is 170-183 DEG C, at this time the solder paste is on the eve of melting, the flux in the solder paste infiltrates the PCB pad and the device end, and due to the high heat transfer coefficient of vapor condensation, if the temperature rising rate of the flux infiltration zone is too fast, the probability of asynchronous wetting of the two ends of the device is greatly increased, and even the device is not completely wetted at one end before entering the solder paste melting zone, increasing the probability of standing monument defect.

[0037] The temperature of the solder paste melting zone is about 183-190 DEG C, at this time the solder paste changes from paste to liquid state, which is the key stage of standing monument defect, if the temperature rising rate of the solder paste melting zone is too fast, the solder paste melting time of the two ends of the device is different, the surface tension is unbalanced, leading to the occurrence of device standing monument defect, so the too fast temperature rising rate of the solder paste melting zone is the main reason for the standing monument defect.

[0038] 2. Key technology of process method for solving standing monument defect in vacuum vapor phase welding.

[0039] The key to solving the serious problem of standing monument defect in vacuum vapor phase welding is to master the process method of adjusting the temperature rising rate and set reasonable process parameters.

[0040] As shown in Figure 2 , the internal structure of IBL VAC745 vacuum vapor phase welding machine mainly includes the bottom heating zone, the heat exchange zone, the condensation zone and the cooling zone, wherein the heating power of the bottom heating zone and the number of layers of the workpiece staying in the heat exchange zone are the key factors affecting the temperature rising rate.

[0041] The heat exchange zone is divided into 5-20 layers from top to bottom. The RF4 board with a thickness of 2 mm is used as the test workpiece, and the temperature rising rate of different layers in the heat exchange zone is tested (the heating power at the bottom is set to 60%). The specific data are shown in Table 1 and Figure 3

[0042] Table 1: The highest temperature and temperature rising rate reached by different layers in the cavity

[0043]

[0044] In summary, the temperature rising rate of the workpiece is proportional to the number of layers staying in the cavity. The greater the number of layers, the greater the temperature rising rate. Therefore, moving the workpiece to stay in the cavity is one of the process methods for adjusting the temperature rising rate.

[0045] The heating power of the heating area at the bottom of the cavity is adjustable. The RF4 board with a thickness of 2 mm is used as the test workpiece, and the temperature rising rate of the 7th layer and the 8th layer is tested by using different bottom heating powers of 40%, 45%, 50%, 55%, 60%, and 65%, respectively. The specific data are shown in Table 2 and Figure 4

[0046] Table 2: Temperature rising rate of the 7th layer and the 8th layer with different bottom heating powers

[0047]

[0048]

[0049] In summary, the temperature rising rate in the cavity is proportional to the bottom heating power. The greater the bottom heating power, the greater the temperature rising rate of the workpiece. Therefore, adjusting the bottom heating power is another process method for adjusting the temperature rising rate.

[0050] By setting reasonable process parameters, the process method for solving the monument defect in vacuum vapor phase welding is to control the temperature rising rate of 170-190°C, ensure that the PCB pads and component soldering ends are completely wetted, and reduce the melting time difference of the solder paste. In order to obtain reasonable process parameters, the same type of board is welded with different temperature rising rates for process verification. The board contains 1695 0402 packaged devices, and the number of monuments generated by different temperature rising rates is recorded.

[0051] The test results are shown in Table 3. When the temperature rising rate is greater than 0.4°C / s, there are monument defects. The higher the temperature rising rate, the more serious the monument defect. When the temperature rising rate is less than or equal to 0.4°C / s, there is no monument defect.

[0052] Table 3: The number of monument defects generated by different temperature rising rates

[0053] ​​

[0054]

[0055] It can be seen that the process method for solving the monument defect of vacuum vapor phase welding is mainly to control the temperature rising rate at 170 DEG C to 190 DEG C to be below 0.4 DEG C / s.

[0056] The qualified rate of the product adopting the vacuum vapor phase welding is only about 30% through the experiment, and after the process parameters are controlled according to the new process method, the qualified rate of the product is increased to more than 99%.

[0057] In summary, the method for solving the monument defect of vacuum vapor phase welding provided by the application adopts the mode of controlling the temperature rising rate in the temperature range corresponding to the soldering flux infiltration area and the solder paste melting area, so that the chip type packaging device will not appear the problems such as the wetting of two ends out of synchronization and the surface tension imbalance caused by the difference between the solder paste melting time of two ends in the welding process, thereby effectively preventing the monument defect caused by the too fast temperature rising rate. Meanwhile, the temperature rising rate control method is simple and easy to implement and can be controlled with high precision.

[0058] It should be noted that, in the present document, the terms such as first and second, etc., are merely used to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or equipment including the element.

[0059] From the above description of the embodiments, those skilled in the art can clearly understand that the application can be implemented by means of software plus the necessary general hardware platform. Based on such understanding, the technical solutions of the application can be embodied in the form of a software product, which can be stored in a storage medium, such as a ROM / RAM, a magnetic disk, an optical disk, etc., and includes a number of instructions to make a computer device (which can be a personal computer, a server, or a network device, etc.) execute the methods described in various embodiments or some parts of the embodiments of the application.

[0060] The various embodiments described in this specification are presented as examples of the application. Each example is provided by way of best mode, and variations of or additions to these examples can be possible. For example, the various embodiments described in this specification can be combined in different combinations. Further, other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. For example, to implement a system embodiment, one can implement a method embodiment and one or more system modules to perform the method embodiment. Each of the various embodiments can be implemented alone or in combination with any other embodiments. It is therefore intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.

[0061] Any modification, equivalent replacement, improvement, and the like made within the spirit and principle of the application shall fall within the scope of the protection of the application.

Claims

1. A method of solving the defect of vacuum vapor phase soldering monument, characterized in that, Comprise: The temperature rising rate in the temperature interval corresponding to the solder flux infiltration area and the solder paste melting area in the lead-containing and lead-free mixed soldering temperature curve is controlled to be not greater than 0.4 ℃ per second by using a target method; Wherein, the solder paste under the solder flux infiltration area is at the eve of melting, and the solder paste under the solder flux melting area changes from a paste state to a liquid state.

2. The method of solving the pedestal defect of vacuum vapor phase welding according to claim 1, wherein, The temperature interval comprises 170 ℃-190 ℃.

3. The method of claim 1, wherein the method further comprises: The target method comprises adjusting the temperature rising rate by moving the workpiece to adjust the number of layers staying in the cavity.

4. The method of claim 1, wherein the method further comprises: The target method comprises adjusting the temperature rising rate by adjusting the bottom heating power.

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