陣列錫球錫裂的四種失效行為模式, 收錄在Robert Darveaux 的"Reliability of Area Array Solder Joints In Bending"文中
Four different failure modes were observed in the bend testing. These are shown schematically in Figure 11.
Failure Modes #1
基板處裂開
In failure mode #1, the test board pad de-laminates from the laminate core. A small amount of epoxy resin usually remains with the pad. Once the pad delaminates, it is free to move up and down as the test board is bent. This causes eventual fatigue failure of the test board trace. A photograph of failure mode #1 after dye-and-pry failure analysis (technique described in Ref [9]), is shown in Figure 12. The laminate core under the test board pad is stained with the dye, indicating that it was failed before the component was pried off the board. Failure mode #1 is typically observed at the harshest bend test conditions (greatest deflection).
dye stain test figure of failure mode#1
Failure Modes #2
Trace or pad 處裂開
Failure mode #2 is also due to test board trace failure. However, in this case, the pad does not delaminate from the laminate core. The trace fatigues and cracks near the region of the solder mask opening. This type of failure mode is most difficult to detect with the dye-and-pry technique.
Failure Modes #3
錫球靠近pad或trace附近的位置裂開
Failure mode #3 is due to solder fatigue failure near the test board pad. It is believed that the crack initiates on the outside edge of the pad where the trace exits. This region of the joint is solder mask defined (no fillet of solder around the side walls of the pad). A photograph of mode #3 after dye-and-pry failure analysis is shown in Figure 13, and a cross section is shown in Figure 14. In the present study, only OSP finish was used on the test boards. Hence, there were no interface failures observed. For test boards with Ni/Au finish, it is possible to observe interface failures at the test board pad interface.
dye stain test figure of failure mode#3
cross section figure of failure mode#3
Failure Modes #4
錫裂在compoonent的位置
Failure mode #4 is due to solder fatigue near the component interface. A photograph after dye-and-pry failure analysis is shown in Figure 15. This failure mode was observed only rarely in the present study, because in most cases the component pad was somewhat larger than the test board pad. No interface failures on the component side were observed in the present study.
dye stain test figure of failure mode#4
In general, failure modes #1 and #2 were observed at the highest stress conditions, and modes #3 and #4 were observed at the lower stress conditions. Also, the size of the trace exiting the test board pad will affect the propensity to observe failure mode #2. As trace size is reduced, mode #2 becomes more prevalent. Also, if the test board is handled too much after SMT process, one observes more of failure modes #1 and #2. Classifying the failure mode was found to be very important in assessing the validity of a particular test result.
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