November 10th, 2006
Folks,
I am sympathetic and concerned about the effect of RoHS complinace on military and other high reliability products. Perhaps an organization like DARPA should take a lead in addressing this issue. I will investigate this concern further in the future. Reader Michael sums up the situation below:
Dr. Lasky,
I appreciate your writing regarding repealing RoHS. Let me just share how the impact of RoHS has dramatically affected our business. Our company is one that supports repealing RoHS, not because of lack of concern for the environment, but because of the applications that our electronic assemblies are used. We are an electronics manufacturer for the military and our products are used in missile detection systems and other military defense systems. The government has strict standards for electronic assemblies and we have received directive from nearly all our customers to not switch to RoHS compliant parts. As you are probably aware, most if not all component manufacturers are discontinuing leaded products and only offering RoHS compliant products. Costs are increasing because in order to comply with customer directives, we are now forced to buy many times more product than we may ever use just to ensure we can provide highly reliable assemblies to our customer. When leaded products run out, there is no choice for us. It is not as simple as converting to RoHS compliant parts and processes when our customers direct us not to switch because of the reliability.
In our business, if our products fail, lives are at stake. I have not found any concrete studies showing that lead free parts and assembly processes are just as reliable as their leaded counterparts when used in strenuous applications. Several weeks ago our company CEO was at a high level meeting with government officials discussing a program we support and there is much concern about switching to RoHS and several folks have shared their experience with RoHS compliance and it wasn't pleasant. Product reliability is in question.
When making televisions, radios, and other household electronics, I can understand how great RoHS might be. But when dealing with products that our service men and women must use to protect themselves and our country, I don't think we should be forced to switch to something less reliable.
Best Regards,
Michael
Don Ballard:
Have you looked into the experiments using lead free solders to reduce whiskering? I just read an article on whisker formation from the SMTA Series called "Whisker Formation Potential in Pb-Free Electroplated Connector Finishes" The following is an excerpt from the article:
Although a truly meaningful tin whisker test will only arise once the actual mechanism for whisker initiation/growth is understood, appropriate acceleration factors are selected and confirmation is achieved. The tin whisker testing methodologies developed thus far use traditional environmental stresses such as elevated temperature, elevated humidity and thermal cycling between temperature extremes.
Tin whiskering performance of a particular finish is known to depend strongly on a variety of factors, including surface oxide condition, electrodeposit thicknesses, composition of the barrier layer, level of residual stress, temperature and time.
The military and aerospace industries have also examined tin on nickel along with other combinations that are much more expensive. Typically, nickel barrier layers in the neighborhood of 1-3 um are thick enough to block interdiffusion but not thick enough to make the interfaces brittle. 12-15 um of tin on 600-800 um of nickel has successfully hindered tin whisker growth.
Many studies have examined specific electrodeposited finishes within controlled experiments using the above mentioned testing methodologies. Within the constraints of the aging conditions, plating chemistries and sample types utilized for studies, several conclusions can be reached. For pure tin electrodeposits, nickel barrier layers were significantly more effective than copper barrier layers in the suppression of whiskering. Matte tin and bright tin over nickel barrier layers did not whisker when subjected to the various environmental aging conditions in several studies. If nickel barriers are as effective as several prominent studies would indicate, the industry may indeed have a solution to the tin whisker problem
Don Ballard:
BTW- here is a good link with reference to the above: http://www.jedec.org/DOWNLOAD/search/JP002.pdf
I am curious as to youir opinion Dr. Ron on the experiments and procedures.
Don Ballard:
http://www.circuitsassembly.com/pdf/0502/0502ca_digital.pdf
The article in full is at the above link.