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July 2011

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From:
Paul Reid <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Paul Reid <[log in to unmask]>
Date:
Thu, 14 Jul 2011 19:10:04 -0400
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I disagree with the stated and implied affect of RoHS, on PWBs expressed in this article. Lead free assembly reduces reliability by 50%. There can be no doubt about that. There are too many studies that confirm lead free assembly significantly degrades reliability.  There are so many studies that demonstrate a reduction in reliability that Rod's contention is almost laughable. We are now faced with increased failures of copper interconnections and dielectric material due to high assembly temperatures. There is an increase in crazing that can support CAF, significant copper dissolution, and cratering in assembly, Switching to lead free in most HDI applications is a significant challenge. Lead free assembly has a profound affect by degrading PWB's organic component (epoxy) due the temperature required and copper interconnection and also the exaggeration of the z-axis expansion of the dielectric.

 

I have heard of anecdotal stories like "We switched to lead free with no problem!" but never have I seen data that suggests lead free does not degrade the robustness of a PWB. It may be some applications have so much extra "reliability", such a large "guard band" build into the product, that there is no affect noted in assembly and the end use environment. But make a small change like say grid size, hole size or layer count and they might be very surprised to find out what worked for years won't work now.

 

There was this guy standing on the corner of the street snapping his fingers.

A business man walks up to him and says "Why are you snapping your fingers?"

The man replied "To keep away elephants."

The business man said "There are no elephants within 1000 miles of here!"

The man replied "See! It works"

 

Anecdotal evidence is compelling, makes good and interesting stories, and sets one up for major error, and embarrassment when offered as grist for the mill of reality. RoHS's affect on the electronic industry, juxtaposed against the benefit to the environment, does not stand up to the scrutiny of critical thinking. It does not appear the decision is based on "good" science or objective evidence. RoHS appears to be feel good legislation that has, over all, minimal benefit and significant negative impact on society.

 

Well, that's my impression at any rate.

 

Respectfully,

 

Paul Reid

________________________________

From: TechNet on behalf of Post, Scott E
Sent: Thu 14/07/2011 2:57 PM
To: [log in to unmask]
Subject: Re: [TN] Lead Free solder has performed well...



I agree that Pb free implementation hasn't been a disaster (with the exception of tin whiskers), but a few years without a bunch of major reliability catastrophes isn't a great indication of equivalent reliability.  Besides the lack of time that's passed, especially for electronics requiring a long service life, there's also the fact that we've designed around some of the weaknesses of SAC alloys.  For example, adding corner bond or underfill to pass BGA drop tests or using multiple smaller ceramic resistors in the place of one larger resistor to pass thermal cycling.  If we'd left our designs alone and only changed the solder alloy we'd be seeing more reliability problems.  In many situations Pb free is not as reliable as SnPb if everything but the alloy is kept equal.

Scott Post
Staff Manufacturing Engineer
P.O.U. 0000-001E-0CTC
2151 E. Lincoln Road
Kokomo, Indiana    46904-9005
765-451-2983 (Phone)
765-451-0287 (FAX)

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Eric Christison
Sent: Thursday, July 14, 2011 12:20 PM
To: [log in to unmask]
Subject: [TN] Lead Free solder has performed well...

http://www.designnews.com/author.asp?section_id=1389&doc_id=231199&f_src=designnews_gnews

"Dr. Ronald Lasky, Dartmouth professor of engineering and a frequent blogger on solder, claims the transition to lead-free was a grand success. "A lot of people claim that lead-free solder is not as reliable as lead-based solder," Lasky told me. "We're now five years into the implementation of RoHS, and we've made $3 trillion work of electronic.
We haven't really noticed any big change in reliability.""

I thought some of you may be interested in the above article.

Regards,


--
Eric Christison
Consumer&  Micro group
Imaging Division

STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom

Tel:    +44 (0)131 336 6165
Fax:    + 44 (0)131 336 6001

The contents of the email are ST confidential.




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