MIGRATION RELIABILITY COMPARISON OF INTERCONNECTION SUBSTRATES: POLYMER THICK FILMS SEEM BETTER THAN REGARDED?

摘要

The production of high-density interconnections for multichip modules (MCMs) requires realizing conductor-systems withvery high resolution and high reliability. The possibilities of increasing the density are determined not only by thetechnological bases but also by those physical and chemical processes that can cause resistive shorts between adjacentmetallization stripes. One of these phenomena is the electrochemical migration, which can lead to a short circuit in thedevice and can cause catastrophic failure. Silver is well known for its inclination to form migratory shorts. It has beenproven that several other metals also show dendritic growth caused by the electrochemical migration, i.e. Cu, Pb, and Sn.The migration reliability of printed wiring boards (PWBs) as well as high-density interconnections is determined by thebehavior of these metals. Polymer thick films (PTFs) use pure silver bearing conductors and they are regarded to have notto very high reliability level, one reason of which is the silver migration problem. If a ranking should be made, they shouldbe much behind the conventional CERMET thick films and printed wiring boards. Their realistic comparison is availableonly through empirical way. In order to have a realistic comparison of the various electronic metallization compositions inconnection with the migration process, experimental procedures have been carried out with low cost silver bearing thickfilm metallization systems fired on aluminum substrates, with copper and tin-lead covered copper metallization on epoxyglassPWBs, as well with silver polymer thick-films on polyester substrate. THB tests (45oC/95%RH/10VDC) wereperformed on the samples and mean time to failure (MTTF) data were compared. Also the effect of pattern resolution wasfollowed on interdigital capacitor structures. The novelty and uniqueness of the paper is the comparison of variousinterconnection systems with the surprising result: polymer thick film approach showed better reliability behavior than itscompetitors among the low cost systems.