Reliability Modeling of Circuit Card Assemblies

Dr. Randy Schueller and Cheryl Tulkoff
Senior Members of the Technical Staff
DfR Solutions

It is widely known and understood that the overall cost and quality of a product is most influenced by decisions made early in the design stage. Finding and correcting design flaws later in the product development cycle is extremely costly. The worst case situation is discovering design problems after failures occur in the field.

Designing for reliability has been "easier said than done" due in large part to the many competing interests involved in a design. For example, the designer is challenged with increasing the product performance while continually reducing the form factor. The reliability engineer may raise concerns about design risks, but without the ability to quantify the potential impact, they are often unable to meaningfully influence the design decisions. Implementing a newly developed reliability prediction analysis tool, Sherlock, will forever change this equation. Before a single product is built, this valuable new tool enables the engineer to import the design files and quantitatively predict the life of the product according to the assumptions made for the user environment.

The failure rate is predicted for thermal cycle fatigue of solder joints and plated through hole vias as well as for shorting from conductive anodic filament (CAF) formation. The software also produces a finite element analysis of the circuit boards showing regions susceptible to excessive board strain during vibration or shock events. The greatest value comes from the ability of the engineers to perform various "what if" scenarios to determine the impact of any number of design choices.

What if I change the mount point locations?

What if I change the via diameters, the spacing, or the copper thickness?

What if I change the laminate thickness or material selected?

What component is at highest risk of failure and what if I change its‟ format?

What is the reliability impact of changing from SnPb to SAC305 solder?

Finally, once the design has been optimized to satisfy the many competing requirements, the software can be used to predict the rate of failure over the lifetime of the product. This information can then be used to more accurately plan for the warranty costs. With margins shrinking in the electronics industry, OEMs depend more on profits from extended warranties. Inaccurate life prediction can cut heavily into this income stream. Under-prediction of the failure rate will lead to cost overruns while overestimating failure will mean lost business to competing extended warranty plans and the setting aside of funds that could instead be used for further product development. This paper will illustrate the capabilities and value that this new tool provides to the various functional units within an electronics manufacturing company.