Could the Red Phosphorous Problem Return?

This blog was very quiet in 2014 but I will try to get off to a better start in 2015.  For those with long memories, red phosphorus in IC packages created quite a lot of concern.  The origin of the problem starts with the use of brominated flame retardants used in electronic materials.   Examples include PBDE (polybromodiphenyl ethers), PBB (poly-brominated biphenyls) and TBBA (tetrabromobisphenol A).  This alphabet soup of chemicals enabled electronic materials to achieve UL 94-V0 flammability requirements. For environmental and health reasons there was and is a push to eliminate halides (i.e. bromine) from electronic materials.  For those interested my more detail, see the references (1) and (2) listed below.  One possible substitute for brominated flame retardants are phosphorus based materials. There are both organic and inorganic phosphorus based flame retardants.  One problem the electronic industry experienced was the use of the inorganic red phosphorus compounds.  Early on it was recognized that this material by itself was too unstable to be used as a flame retardant.  Therefore there were efforts to stabilize the red phosphorus powder. One development was the stabilization by means of encapsulating the red phosphorus spheres with a thermoset resin following an initial coating of aluminum hydroxide.  By 1999 Sumitomo began shipping red phosphorous in molding compounds supplied to the semiconductor industry.  Semiconductors made with the material began to fail after a short time in the field.  In 2001 National Semiconductor issued a product alert warning of early failures.  In 2001 , Maxim also issued an product alert.  The cause of the failures was the breakdown of the aluminum hydroxide coating allowing moisture to react with the phosphorous.  One by-product of this reaction is phosphoric acid which then leads to leakage paths within the IC package. In 2002, Sumitomo announced the end-of-life for this category of flame retardants.  

Certainly the IC industry learned a painful lesson and I wouldn’t expect a major IC supplier to repeat the mistake. But is that the end of the story?  We shouldn’t be too sure.  For one thing memories are short especially in the world where people change positions much more frequently.  Someone once said that problems tend to repeat themselves every 7 years.  That may not be a rule but the idea is valid, i.e. that people either forget or change positions and therefore problems can come back.  As I said, I would not expect the IC industry to repeat this mistake but what about other commodity areas?  I am thinking specifically of the cable and connector industry.  Here is an industry that is ready for such a mistake.  Price pressures exist and large companies tend to contract out products to smaller sub-contractors. These sub-contractors may not have much oversight and may even make changes without notification.  The changes could even me made by a process engineer who is working to get a bonus for cost savings.  So my prediction is that it is in this area where a problem could occur.  So if you see a mysterious corrosion problem in a cable assembly.  That is, a problem where the environment is clean but the connector metal is corroding, don’t overlook this failure mechanism.  Do elemental and chemical analysis to see if phosphoric acid is being release from the molding compound.

References

1.     1.    M. Pecht, Y. Deng, Electronic Device Encapsulation using Red Phosphorus Flame Retardants, Microelectronics Reliability 46 (2006), pp 53-62.

2.      C. Hillman, Red Phosphorus Induced Failures in Encapsulated Circuits, DfR Solutions white paper.