The Mechanical Performance of Sn-Pb Solder Joints on LTCC Substrates

The assembly of ceramic components often uses soldering technologies to attach metal structures to the ceramic base material. Because many suitable solder alloys do not readily wet and spread on ceramics, a metallization layer is deposited on the latter to support wetting and spreading by the molten solder for completion of the joint. The metallization layer must be sufficiently robust to retain its integrity through the soldering process as well as not negatively impact the long-term reliability of the joint. A study was performed to evaluate the mechanical properties of solder joints made to a 0.200Ti/W-4.0Cu-2.0Pt-0.375Au (mu m) thin-film metallization deposited on low-temperature co-fired ceramic (LTCC) base materials. The solder joints were made with the 63Sn-37Pb solder (wt-%, abbreviated Sn-Pb). A pin pull test was developed to measure the tensile strength of the solder joint as a function of soldering parameters. Failure mode analysis was a critical metric for assessing the roles of interfaces, bulk solder, and the ceramic on mechanical performance. The Sn-Pb solder joints experienced a nominal strength loss with increased severity of the soldering process parameters. The strength decline was attributed to changes in the solder joint microstructure, and not degradation to the thin film structures.