In a message dated 10/6/99 1:58:29 PM Eastern Daylight Time,
[log in to unmask] writes:

<< Nancy- just for the edification of all who responded-can you share with us
 what the root cause of your problem was- might keep some of us from
 repeating the same mistake...

 Thx
 > Bill Davis, Ph.D.

Bill and Nancy

We have found out here at CSL Inc. that much of the industry problems
associated with electromigration are related to bare board cleanliness (for
both No Clean and Water Soluble fluxes), but not always, we have seen high
levels of chloride, or bromide, or Methane Sulfonic Acid (MSA), or Citric
Acid activators in water soluble fluxes and solderpaste improperly cleaned
(tap water???) cause dendrite growth.  We also see electrical leakage
failures in the field due to No Clean flux residues that are not completely
heat activated and can absorb moisture and create a leaky circuit that will
fail in the field but test fine when it comes back to the bench and then
becomes labeled as No Trouble Found and set aside.

To address your question about root cause of electromigration three things
must be in place.  First - voltage difference (as little as 1.5 volts),
second - fluid media only monolayers thick (generally water but not always),
third - a corrosive residue to cause the deplate of the anode, conductive
residues will cause leakage but not electromigration.  We have seen even gold
electromigration failures with very high chloride residues from water soluble
flux hand soldering process.

We have a number of published case studies on this subject if you are looking
for data check out WWW.Residues.com and look in the case study library.

We have also found that the process control tools used on the production
floor will not show how clean or dirty an assembly is but work as an
indicator of process changes from a historical baseline.  We have used Ion
Chromatography and SIR testing to understand the type and level of process
residues, as well as, their impact on electrical performance.

Thanks for the soap box
Terry Munson
[log in to unmask]
765-457-8095
Residues.com

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