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May 2011

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Subject:
From:
"Goodyear, Patrick" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Goodyear, Patrick
Date:
Thu, 12 May 2011 20:41:38 -0700
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Thanks and great responses.   I am not using lead free to rework old boards, rather as we purchase newer equipment from vendors worldwide, Yokogawa, ARIVA, Algent. How do you determine what to use for repair if there is no standard as to the type of lead free alloys used in that industry?  Does a company use whatever is cheapest at the time?   Are there any tests that can be performed that can determine the materials used? 

I will always use 63/37 as the reliability is better.   Have been inspecting a bunch of 40 year old boards that have had solder failures around a certain resistor that is off mounted on the boards and they are single sided with no strain relief on the component side.   These boards were manufactured in the late 60's by Westinghouse or their supplier, which are most likely no longer in business.   We have been remounting the resistor with eyelets installed to give them a little more support.   These are the issues we deal with.

Pat Goodyear 
Control Tech
Pacific Gas and Electric. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Thursday, May 12, 2011 9:47 AM
To: [log in to unmask]
Subject: Re: [TN] Repair / Rework on non-in-house RoHS compliant boards

Ok, let's start with the premise "Build To Print".
If the assembly drawing stipulates the alloy type to solder the assembly with (and nearly all do), then you have a print requirement to deal with. Just because you rework an assembly 20 years later and some blue suit in the EU says it is OK does not mean diddlysqat. RoHS rules simply do not apply to exempt products (and for good reason! I don't believe anybody really doubts there are reliability issues to contend with.) Nevertheless, ignoring all that, why would you ever want to rework something that was built with 63/37 solder with any other alloy?
In order to do so, you are violating a print requirement. You would need a waiver or an ECN or some other written permission from the customer to do so. I doubt any knowledgeable military customer would allow you to do so without some type of proper qualification to justify doing so, and a letter from the EU bureaucrat is probably not going to get them all warm and fuzzy. For product that is not "high-rel", that does not mean it doesn't matter if you mix alloys. We start with the philosophy that it does. 
And every application is different. You cannot make a blanket assumption that any product built with 63/37 will be OK if reworked with some other alloy.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Thursday, May 12, 2011 10:54 AM
To: [log in to unmask]
Subject: Re: [TN] Repair / Rework on non-in-house RoHS compliant boards

There are known compatibility issues with some alloys and joint configurations and in your case you would have determine the unknown ones.
My question to you would be: Why go there?
1) ROHS allows the use of leaded solders for repair of pre ROHS products.
2) Infrastructure [power stations ] is presently excluded from ROHS along with anything else where high reliability is required  (Aviation, medical, automotive etc).
3) Suggest that even assuming Pb free solders were environmentally superior (and some doubt this), in your application the environmental impact of using Pb-free solders would be negligible and far outweighed by the possible consequences of unreliable joints. 
Regards
 
 
Mike
ü Please consider the environment before printing this e-mail -----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Goodyear, Patrick
Sent: Sunday, May 01, 2011 7:12 AM
To: [log in to unmask]
Subject: [TN] Repair / Rework on non-in-house RoHS compliant boards

As a technician that does frequent board level repair rework some
questions have come to mind.   While the majority of my work is legacy
i.e. vintage (1968) we will face these concerns in the near future.  The boards I primarly work on are Nuclear graded Class IE, (high reliability, seismically qualified, etc.) high dollar boards, typically in the 3-10g range and are not throw-aways, most have components that are no longer manufactured. 
I am looking to the industry to find best practices, this is one of the
places that was suggested for posting.   Any help you can give me would
be appreciated. 

With pre RoHS solders most if not all of major manufacturers used 63/37 solders and repair rework was easy, one just used 63/37. 

With the adoption of RoHS controls and the subsequent use of many different alloys of lead free solders, (at least 6 I know of), the following comes to mind:
1. Are there compatibility issues mixing between the various alloys of
lead-free employed currently in electronics manufactures?   In strength
and reliability primarly. 
2. How does the technician determine the correct alloy of lead-free solder to use? 

3. How does the technician determine what alloy was originally used by the manufacturer? 

4. Will IPC 7711A / 7721A standards be updated to delineate alloy determination and / or an alternate methods for the complete removal of lead-free solders and subsequent repair using 63/37 or lead-free alloys?
Pat Goodyear
Control Technician
Pacific Gas and Electric Company
Diablo Canyon Nuclear Power Plant
PO Box 56
Avila Beach, CA. 93424
805-545-4312 


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