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February 2010

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From:
Bob Landman <[log in to unmask]>
Reply To:
Bob Landman <[log in to unmask]>
Date:
Mon, 15 Feb 2010 16:31:03 -0500
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Kevin,

I would think that, while it costs more, the use of nitrogen when doing ImAg would help alleviate the problems you mention?  I understand it costs more but I wonder, isn't it worth the difference in the end results?  I recall a recent article in SMT on the use of nitrogen and one of the factors that significantly improved was the reduction in oxidation so the flux didn't have to be so aggressive?  How significant a difference in cost is the use of nitrogen?

Bob Landman
H&L Instruments, LLC
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Glidden, Kevin
Sent: Monday, February 15, 2010 1:20 PM
To: [log in to unmask]
Subject: Re: [TN] Lead-free soldering on ImAg

Dave, Did your investigations utilize double sided reflow as well as single sided, plus secondary soldering?  Do you see degradation to solderability after multiple soldering processes? 

We utilize ImAg finish in a traditional SnPb process, and we DO sometimes see solderability issues.  Even normal SnPb reflow temperatures can accelerate the oxidation on the second side pads before they are printed and placed.  The two reflow passes required for double sided SMT can make any post-SMT soldering (such as for hand soldering components or wire attachment) even more difficult.

Your materials used (flux types & activity levels) can drastically effect whether or not surface oxidation can be overcome to allow proper wetting.  Just as important (if not more) is controlling the exposure of the PCB to sulfur compounds or moisture, both of which can begin and accelerate the oxidation.  Putting controls in place to ensure proper packaging and moisture resistance can go a long way in preventing the PCBs hitting the line right-off-the-bat with minor oxidation already started.  This too is included in the 4553....

You also mentioned silver thickness, and I have found more favorable results utilizing the "thick" designation, not the "thin", both of which are allowed in 4553....



-----Original Message-----
From: David D. Hillman [mailto:[log in to unmask]]
Sent: Monday, February 15, 2010 11:20 AM
To: [log in to unmask]
Subject: Re: [TN] Lead-free soldering on ImAg

Hi Ioan! I have conducted a number of leadfree soldering investigations with SAC405 and SAC305 solder paste using Immersion silver pwbs in accordance with the IPC-4553 specification and have had no issues. The higher leadfree processing temperatures tend to degrade all printed wiring board surface finishes a bit faster than in tin/lead processing.  I recommend you investigate to see if the Immersion silver meets the IPC
4553 requirements.

Dave Hillman
Rockwell Collins
[log in to unmask]




Ioan Tempea <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
02/15/2010 10:06 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to Ioan Tempea <[log in to unmask]>


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Subject
[TN] Lead-free soldering on ImAg






Dear Technos,

 

I know the ImAg has been discussed over and over and with the same 
results, very good and reliable finish.

 

My little something now is all the proponents were mainly in high-rel 
applications (so SnPb solder most likely) and I do not remember if RoHS on 
Ag was discussed. I know it wouldn't make sense for this finish not to 
work with SAC305 pastes, but I just want to make sure.

 

 We have, guess what, wetting issues on two different boards, from the 
same supplier. We have tried playing with the reflow recipe, no 
improvement. The batch finished, but now we are attacking a few more 
different models 

from the same PCB fab.

 

So, did anybody have issues with ImAg because they were on lead-free? Any 
particular parameters that are not a happy ingredient, like specific types 
of paste, specific solder recipe milestones?

 

If it were the PCBs, what could be wrong except for the Ag thickness? I 
mean XRF analysis would be cheaper than x-sectioning...

 

Thanks,

 

Ioan Tempea, ing.
Ingénieur Principal de Fabrication / Senior Manufacturing Engineer
T | 450.967.7100 ext.244
E | [log in to unmask] <mailto:[log in to unmask]> 
W | www.digico.cc <http://www.digico.cc/> 

 
 N'imprimer que si nécessaire - Print only if you must

 


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