Measurement Note - Crack Detection Methods For Lead-free Solder Joints

This Note describes the suitability of a number of techniques of potential use in studying cracking in lead-free solder joints, and hence their use in assessing joint lifetimes. Cracks induced into solder joints of chip resistors on FR4 substrates, were studied using micro-sectioning, dye penetration, mechanical test and thermal conductivity techniques. The work previously reported [1] has been used as the basis for comments, especially regarding understanding of the tests themselves. The work has shown that those techniques traditionally used to study lead-based solder joints can be used for assessing lead-free solder joints. Although micro-sectioning is suitable for locating and imaging joint cracking, especially when the section is examined in a SEM, it is not very suitable for quantitative analysis of cracks or their detection in small components. Dye penetration techniques allow a better characterisation of cracks in the horizontal plane and can provide a quantitative measure of the cracked surface area. Shear testing is a proven method [2] for evaluating not only the degree of crack propagation and damage to the solder joint, but also the general strength of the joint. The other methods considered (3 and 4-point bend tests, pull test and heat transfer) have severe limitations and are unsuitable for studying cracks in electronics solder joints. Milos Dusek & Christopher Hunt April 2004 DEPC-MN 001