Analytical and numerical analysis of impact pulse parameters on consistency of drop impact results

Abstract

JEDEC standard for board level drop test of handheld electronic products addresses test requirements in details. However, the effects of impact pulse are not emphasized there, which should be one of the key variables that affect the solder joint reliability during drop impact. In This work, effects of impact pulse on dynamic responses of PCB and solder joint reliability under drop impact are investigated by both theoretical analysis and numerical modeling. All the parameters related to impact pulse including area under impact pulse, pulse duration, pulse shape, peak acceleration, peak width, and peak location can affect the peeling stress in critical solder joints and thus affect solder joint reliability performance under drop impact. There will be some difference in solder joint reliability performance as long as there is some variation in impact pulse. The importance of impact pulse is obvious. Numerical modeling using input acceleration (Input-G) method is adopted to investigate the consistency of drop test results which normally have high variations from tester to tester or supplier to supplier due to difference of actual test impact pulse. The actual impact pulse is directly input to drop impact model and variations of solder joint peeling stress can be obtained and compared. The findings show that there will be large variation of test result even though the impact pulse used by different companies are all within the JEDEC test specification which is believed to be too loose. Therefore, there is a must to control impact pulse tightly or the test results are not comparable from different testers or component manufacturers. Thus, electronic product manufacturers should have some strategy to minimize such effects for component qualification or selection. The stress level under different test conditions are also examined. Numerical modeling makes it possible to convert the drop test result from one test condition to another test conditions without performing additional drop tests, and thus saving time and cost. Acceleration factors for different test conditions may be obtained. Most importantly, a life prediction model can be built based on a carefully designed experiment.