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January 2009

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Tue, 27 Jan 2009 12:36:08 -0600
Content-Type:
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text/plain (115 lines)
Joyce is correct.
When soldering to Pb95 or the more common Pb90 solder balls used on CGA
(ceramic grid arrays) such as PowerPCs, etc. standard 63/37 solder is
used both for the ball attachment to the CGA and to the circuit board.
You do not need to exceed temperatures for standard 63/37, as you do not
melt the Pb90 or Pb95 solder balls, you simply solder to them. You
should not attempt to melt the balls, the components are usually not
made to handle those types of temperatures.
So if you wish to attach these types of Pb95 balls to a laminate
material, you only need to print standard 63/37 solder paste onto the
laminate, place the balls into the solder paste, and send the package
through a standard reflow profile, say 217 deg. C. max. Later when you
solder the components to the PWB, the same process is used. The Pb95
ball never goes into liquidus, but a small amount is dissolved into the
Sn63Pb37 solder when it is molten, and this provides the solder joint
connection.
In the case of the PowerPC-type of components, the reason the Pb95 ball
is used is to provide the maximum compliancy between the component and
the board to accomodate the delta CTE between the relatively rigid
aluminum oxide component body and the standard FR-4 substrate. Pb90 or
Pb95 is a very soft alloy.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, January 27, 2009 11:21 AM
To: [log in to unmask]
Subject: Re: [TN] C4 attach to organic laminate material

Why you need to go to 290? The 63 only melt at 183 last time I checked. 
--------------------------
Sent using BlackBerry


----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Tue Jan 27 10:26:21 2009
Subject: [TN] C4 attach to organic laminate material

I've been provided with a C4 bumped die, peripheral contact pads, 200
micron pitch, and the alloy is Sn5Pb95 (classic C4, melting point approx
290C).  Someone suggested attaching this to a BGA carrier substrate
(core with low elastic modulus SLC layers to absorb the CTE mismatch)
using Sn63 solder paste.  Tough printing job, but possible.  However, I
don't believe we can get this laminate material up to 290C, so the alloy
mix will be incomplete, meaning a likely brittle zone in the attach.

Only thought I have is using LTCC or HTCC instead of the organic
laminate.

Any other ideas out there?  Anyone do reliability studies with this type
of attach?  Any input would be appreciated!

Wayne Thayer



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