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Monday, November 15, 2004 - 8:00 AM

PCB-SMT Assembly Failure Analysis

N. J. Armendariz, Intel, Hillsboro, OR

Assembly of electronic components to typical printed circuit boards or substrates involves using a combination of both surface mount technology (SMT) and through-hole processes (wave soldering) Figure 1. The critical second-level interconnect (SLI) is primarily a metallurgical connection made between the component surface metallization via a eutectic Pb/Sn solder composition in the form of a solder ball or paste or both and the PCB surface metallization. The SLI is required to provide both electrical conduction and mechanical strength and survive stringent use conditions over a period of time (reliability).

The SLI is formed during conventional SMT-surface mount technology processes involving solder-paste printing, pick-and-place machines and high temperature melting processes of the component leads and/or solder balls in a reflow oven and/or THM through-hole-mount components formed using solder wave processes. Both SMT and THM processes have typically used a eutectic mixture of Sn and Pb and will increasingly transition to higher melting temperature lead-free compositions of Sn, Ag and/or Cu.

Before the analysis begins a brief review of the DFA-design for analysis test approach or test plan will be described, which begins with a typical non-destructive to destructive analysis, Figure 2. Then, a collection of typical failure analysis case studies are presented from a range of SMT development, production and actual product field failures under various use conditions and detailed with their respective failure mode(s) and mechanism(s) with the latest LF-lead free modes and mechanisms recently characterized as listed below:

Each of the particular case studies analytical metrologies are discussed with the appropriate materials analysis recommended and the metrology, which facilitated in reaching root cause and feedback for implementing corrective action in a timely and actionable manner. In particular, advanced metrology methods, such as D3PT (Dye Penetrant Package Pull Testing) and MHT-(Microhardness Testing) will also be discussed in detail.