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February 2008

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TechNet E-Mail Forum <[log in to unmask]>, "Kane, Amol (349)" <[log in to unmask]>
Date:
Tue, 26 Feb 2008 16:05:46 -0500
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TechNet E-Mail Forum <[log in to unmask]>, Guy Ramsey <[log in to unmask]>
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From:
Guy Ramsey <[log in to unmask]>
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Here is the rule of thumb from the EMPF Boot Camp: Four grams per square
centimeter of solderable surface area on the device or board, which ever is
less. You need a pretty good scale and take careful measurements to use the
formula. It is a conservative rule of thumb. I have pushed it and still had
good process results. It is good for SnPb solder. 

We have done a lot of Pb-Free double side assembly, at NPI-Proof of Concept
quantities. Most new designs are well within the ratio above and are fine.

SMT style RF connectors will fall off. Relays like the Coto 9852-05-00 and
NEC UB2-5NJ relays may stay on but our process resulted in some disturbed
solder joints. They must have been darn close to falling off.

Good luck
Guy


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Amol (349)
Sent: Tuesday, February 26, 2008 3:17 PM
To: [log in to unmask]
Subject: [TN] Component Suitability for Second Side Reflow

Dear Technetters,
Where would I be able to find guidance on the suitability of a particular
component for second side reflow?. Obviously, the weight of the component on
the bottom side has to be <= by the solder surface tension force to prevent
the component from falling off the board during reflow. Is there literature
available for calculation of the maximum wt of a component that can be
safely put on a pad, knowing the pad geometry, solder volume and lead
surface area?

Sounds simple enough....until you go to do the actual calculation.

Any pointers would be greatly appreciated.

Thanks,
Amol





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