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May 2009

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From:
John Goulet <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Mon, 18 May 2009 00:18:18 +0000
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Thanks. did you have any ideas about the shelf life of the components and buying direct versus distributors for the reasons listed? 
----- Original Message ----- 
From: "Werner Engelmaier /*" <[log in to unmask]> 
To: [log in to unmask] 
Sent: Saturday, May 9, 2009 3:07:07 PM GMT -05:00 US/Canada Eastern 
Subject: Re: [TN] Rohs SMT parts and shelf life 

 John, 
What needs to be always understood is the fact that you do NOT solder to any of the surface finishes like tin, silver, gold palladium, etc. but to the metal these surface finishes are protecting. 
So, the profiles need to be adjusted for the Liquidus temperature of the solder alloy and to a lesser extent to the the solubility of the metal soldered to in the solder. The latter means that if you solder to nickel [ENIG, Alloy 42] you may need to run a somewhat higher peak reflow T. 
Werner 


  


  

-----Original Message----- 
From: Bev Christian <[log in to unmask]> 
To: [log in to unmask] 
Sent: Sat, 9 May 2009 11:30 am 
Subject: Re: [TN] Rohs SMT parts and shelf life 










John, 
I had a little trouble understanding part of your e-mail, but I think I got the 
gist of it. No, you do not need a different reflow profile for good tin parts 
any more than you need a different profile for silver, gold or palladium 
finished components. You either have oxidized parts, dirty parts, bad paste, 
wonky profile. Other TechNetters will have other suggestions I'm sure. 
Bev 
RIM 

----- Original Message ----- 
From: TechNet <[log in to unmask]> 
To: [log in to unmask] <[log in to unmask]> 
Sent: Sat May 09 11:03:43 2009 
Subject: [TN] Rohs SMT parts and shelf life 

My concern is that when purchasing buys directly from the manufacturer use know 
the date of manufacture. 

When you buy from a component distributor or when you have to build from 
consigned parts supplied by the customer you don't know the date of manufacture 
and have no idea how the parts were stored and repackaged. 

We?would like?to generate an Iso procedure relative to this issue and would like 
some advice. 



What I'm seeing are circuits boards that have been reflowing perfectly for? 
quite some time are now built with more and more components that are plated with 
100% tin. Soldering to tin with a eutectic?OA solder paste shouldn't cause a 
problem if the?leads or termination on QFNs,?a bigger problem?are not oxidized 
or contaminated. 

I checked on the internet to see if?you need to adjust the profile when 
soldering to tin coated parts with? eutectic solder but found nothing. You get 
two?sets of profile families, one for eutectic and one for?Pb-free. Nothing for 
a mix so I'm leaning toward a contamination or age problem. ?? 

Thanks for any help you can offer. 

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