科技报告详细信息
A Study on Effects of Copper Wrap Specifications on Printed Circuit Board Reliability
Sood, Bhanu ; Shue, John [Point of Contact] ; Leitner, Jesse ; Daniluk, Kelly ; Sindjui, Lionel-Nobel ; Barney, Richard
关键词: CIRCUIT BOARDS;    PRINTED CIRCUITS;    COPPER;    PLATING;    MANUFACTURING;    RELIABILITY;    MATERIALS TESTS;    THERMAL SIMULATION;    STRESS ANALYSIS;    FAILURE ANALYSIS;   
RP-ID  :  GSFC-E-DAA-TN64591,GSFC-E-DAA-TN65527,GSFC-E-DAA-TN64620
美国|英语
来源: NASA Technical Reports Server
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【 摘 要 】
During the manufacturing of Printed Circuit Boards for a Flight Project it was found that a European manufacturer was building its boards to a European standard that had no requirement for copper wrap on the vias. The amount of copper wrap that was measured on coupons from the panel containing the boards of interest was less than the amount specified in IPC-6012 Rev B, Class 3. To help determine the reliability and usability of the boards, three sets of tests and a simulation were run. The test results, along with results of simulation and destructive physical analysis are presented in this report. The first experiment involved subjecting coupons from the panels supplied by the European manufacturer to thermal cycling. After 17000 cycles the test was stopped with no failures. A second set of accelerated tests involved comparing the thermal fatigue life of test samples made from FR4 and polyimide with varying amounts of copper wrap. Again, the testing did not reveal any failures. The third test involved using interconnect stress tests coupons with through hole vias, and blind vias that were subjected to elevated temperatures to accelerate fatigue failures. While there were failures as expected, the failures were barrel cracks, not in the wrap location. In addition to the experiments, this report also discusses the results of finite element analysis using simulation software that was used to model plated through-holes under thermal stress using a steady state analysis, also showing the main failure mode was barrel cracking.The tests show that although copper wrap was sought as a better alternative to butt joints between barrel plating and copper foil layers, manufacturability remains challenging and attempts to meet the requirements often result in features that reduce the reliability of the boards. Experimental and simulation work discussed in this study indicate that the standard requirements for copper wrap are not contributing to overall board reliability, although it should be added that a design with a butt joint is going to be a higher risk than a reduced copper wrap design. The study further shows that procurement requirements for wrap plating thickness from Class 3 to Class 2 would pose little risk to reliability (minimum 5 μm/0.197 mil for all via types). Experimental results corroborated by modeling indicate that the stress maxima are internal to the barrels rather than at the wrap location. In fact, the existence of Cu wrap was determined to have no appreciable effect on reliability.
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