LEAD-FREE SOLDERING SOLUTION FOR OVERMOLDED HYBRID MCM-L PACKAGES
Author: Steve Liang Company: Conexant Systems Date Published: 1/25/2000
Pan Pacific Symposium
Abstract: The newly developed hybrid multi-chip module (MCM) micro-electronic packages contain mixed interconnections of single or multi-dies and a number of surface mount devices (SMD) on laminate substrates. These hybrid MCM-L packages have the advantage of providing an integrated system solution at a short design and production cycle and low cost. One of the hybrid MCM-L package types uses epoxy encapsulation through transfer molding, which offers improved reliability and reduced packaging cost. However, the interaction between epoxy molding compound and the SMD solder joints may introduce functional failure during application of package. Upon molding, the solder joints in the epoxy-encapsulated package will be completely contained and restricted by the surrounding epoxy. The hybrid micro-electronic package will eventually be soldered onto application boards using standard eutectic solder by surface mount technologies (SMT). During SMT soldering process, the package will be exposed to an extensively heating environment. The peak temperature of soldering process generally exceeds the melting temperature of standard eutectic solder. In an epoxy encapsulated package, the thermal expansion mismatch between the solder joint and the surrounding epoxy creates a highly stressing condition onto the melted solder and forces it to flow. The flowing and wicking of solder may short the different terminations leading to functional failure. To solve this problem, a lead-free soldering system has been developed for the overmolded hybrid MCM-L packages. In current study, the effectiveness of this lead-free soldering system for the overmolded hybrid MCM-L packages has been investigated. Factors such as lead contamination, moisture levels and processing temperatures that may influence the solder joint stressing condition and solder melting temperature were also investigated.