Q&A with Werner on Solder Joint Reliability

IPC: What are the key considerations for assuring solder joint reliability?
Engelmaier: The key issues that need to be met to assure to reliability of solder joints are a proper “Design-for-Reliability” (DfR) to avoid premature solder joint failures due to cyclic creep-fatigue, and good manufacturing quality to avoid infant mortality failures.
DfR takes into account the severity of the intended operating environment, the important design details, the design life as well as the consequences of functional failure.  Doing so, assures that the solder joints will not fail prematurely due to creep-fatigue in operation. 
Inadequate quality can cause premature failures for a variety of causes, which include issues like “head-on-pillow,” black pad, gold-embrittlement among others.  A proper root cause analysis can determine the reasons for the failures and suggest solution options to prevent future failures. 

IPC: What about solder joint reliability for Pb-free solders? What are the important changes affecting reliability?
Engelmaier: The most important change with the change to Pb-free solders is an increase of the Solidus temperature of the solders from 183°C to 217°C.  That means that the minimum soldering temperatures increase from 203°C to 237°C or more since the SAC solders are not eutectic alloys.  This, in combination with the Pb-free solder alloy metallurgy, makes assembly processes significantly more challenging and assuring reliability more difficult.  

Interested in learning more?

Engelmaier will be teaching a webcast series for IPC in September. On September 15, Engelmaier will teach the most important fundamentals for a successful DfR.  While it cannot take the place of a full workshop, the most important solder characteristics, damage mechanisms and DfR-measures to assure long-term reliability will be presented and discussed. 
On September 16, 2009 he will highlight the solder joint failure modes caused both by inadequate quality and DfR together with the damage mechanisms causing these failure modes.  He will demonstrate these issues with root cause analysis examples from his consultant activities. And finally, on September 17, he will discuss the impact of the lead-free solders and their processing on electronic product reliability.  He also will show the newly developed models for SAC 405, 305, 205 and 105 as well as SnAg Pb-free solders and discuss the ramifications for both accelerated testing under IPC-9701 and product reliability.

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