TECHNET Archives

October 2013

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Mike Fenner <[log in to unmask]>
Reply To:
Date:
Wed, 23 Oct 2013 19:03:19 +0100
Content-Type:
text/plain
Parts/Attachments:
text/plain (85 lines)
Guy
Type 3 powder size won't hack it. In practice Type 4 particle size is not
that much different from type 3 from some suppliers, but in theory you
should be able to print it.
T5 would enable you to fiddle around with stencil thickness and reductions
but will be relatively expensive, could limit your effective supplier base
and alloy choice and likely will put out lead times. 
Assuming you get an even print you will end up with the right volume of
solder for a 25um reflowed deposit but you might have some problems with
actual reflowed height according to how the surfaces wet and the spread you
get. I imagine you are doing this lead free so this will tend to wet in
place on the non gold surface but will spread on the gold side. Depending on
the thickness of the foil. You haven't dimensioned that so you are anywhere
from getting a solder joint, dissolving Au completely to having high
intermetallics and so on depending on everything including time over
liquidus (as short as possible) and cool down rate( as quick as possible). A
laser zap as mentioned seems attractive. You might need to go to a tin free
alloy. No tin and no lead alloys do exist, but perhaps not in T5 powder. 
I imagine your assembly does not consist of just the one solder joint so
what are you doing with all the others, are they regular alloy joints?
There are some alloy and process combinations that would likely work without
the above issues but would need to have a better understanding of your
application than you might be prepared to share on an open forum.

Regards 
 
Mike Fenner 
BS&P
M: +44 [0] 7810 526 317 
T: +44 [0] 1865 522 663

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Wednesday, October 23, 2013 3:04 PM
To: [log in to unmask]
Subject: [TN] requirement for thin solder joint.

Hi all, 

We would like to solder a thin gold foil, with some magic on top, to a PWB.


The foil and pad are round, about 560 um in diameter. 

We want the solder connection to end up less than 25 um thick.  So, we are
trying to print with a 50um thick stencil, and 20% reduction, the stencil
aperture is 460 um diameter.  So, area ratio, or aspect ratio look great,
printing shouldn't be a problem.  

 

Print results were inconsistent.  

 

This morning I realize that many of solder paste spheres are over half the
thickness of the stencil.  And the rule of thumb that five spheres should
fit across the aperture for good paste release.   Well, what about the
thickness of the stencil versus the diameter of the spheres? 

 

Has anyone out there wrestled with this problem?  Maybe I should be using a
thicker stencil, and push the aspect ratio a bit more. 

 

Thoughts? 

 



______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________



______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

ATOM RSS1 RSS2