Rework Challenges And Solutions For Solder Joints Under Constant Mechanical Load From Gold-Plated EMC Springs
Authors: Wayne Zhang, PK Pu, and Sven Peng, and Alec Chen, Hill Liu, Tracy Cai Company: IBM Corporation and Wistron Corporation Date Published: 10/16/2011
Abstract: Springs that provide electro-magnetic compatibility (EMC springs) are widely used in the electronics assembly industry. However, the industry has little experience in reworking applications with “constant” mechanical loading on solder joints. This paper investigates a solder crack issue which occurred in solder joints under the application of constant mechanical loading from EMC springs. To understand the failure mode and root cause of the issue, multiple experiments were conducted involving different factors including soldering tools and temperature settings, pre-tinning on the EMC springs, pre-heat of the printed circuit board assembly (PCBA) etc. Construction analysis including cross-section and SEM/EDX were utilized to check the intermetallic compound (IMC) layer status and possible contaminants. A final solution was developed following the result of the above analysis. The conclusions from this paper are that the material of the gold-plating layer, appropriate rework method and the thermal profiles on the solder joint are the key factors that will lead to a reliable rework result on this kind of EMC spring. This activity was a joint effort between OEM and EMS engineering teams.