source:Industry News release time:2021-04-27 Article author:Victoria Popular:pcb
1. Problem background
Recently, among the batch of products sent to foreign customers by Weienchen Electronics, a certain percentage of the products cannot be turned on in the feedback of the terminal market. It was found that the BGA on the motherboard fell off after the pcba patch. Most of the PCB solder joints are disconnected from the IMC layer on the solder ball side, and their fractures show brittle fracture characteristics, and a small number of solder joints are disconnected from the PCB substrate. We have reported related problems to customers in the early circuit board proofing.
Analyzing that BGA completely falls off from the PCB substrate is a relatively rare failure mode, which is generally caused by a drop in elevation during transportation.
The complete fall of the BGA usually occurs in such a scenario: a heavier radiator is attached to the BGA, and the IMC is thicker. From the perspective of the peeling phenomenon, a small part of the solder joints are disconnected from the PCB substrate. This is a typical over-stress or impact stress fracture feature, indicating that the board has over-stress operations (such as transportation drops). The brittle fracture of large-scale solder joints in the production of integrated circuit boards is either due to the super thick MC or the existence of gold brittleness. Therefore, the focus of the analysis is on the IMC form and composition of the failed BGA.
2. BGA slice analysis after welding
The surface treatment of this BGA carrier board is ENIG, and the production conditions are used for reflow soldering, and the solder balls are sliced and analyzed. The slice image is shown in Figure 7-68. It can be observed that the MC on the BGA side is massive and super thick, which meets the conditions for causing BGA to fall off.
In addition, it is possible that there are too many ternary alloys in the IMC composition.
Among them, in the process of reflow soldering, an inappropriate temperature curve may be adopted to cause the production of ultra-thick IMC, which becomes the main factor that causes the BGA to fall off completely.
After a joint search with the customer engineer, the final solution is:
1. Reinforce the BGA with glue to improve the anti-drop ability during transportation and use.
2. Adjust the temperature curve and control the welding time.
When customers process PCBA patches in large quantities, this problem never reappears. In many cases, we don't worry about the problem, but everyone's attitude to solve it.
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