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November 2005

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Subject:
From:
"Stadem, Richard" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard
Date:
Tue, 22 Nov 2005 12:53:07 -0600
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A pad the same size as the end termination or only slightly larger, say
.005" on three sides, is desirable for chip caps and resistors. It
provides the optimum amount of solder without additional unecessary
solder that can lead to chip cracking issues.
And whenever you need to rework these, you should never touch them with
a solder iron as that will thermally shock them and also lead to
cracking, depending on the type.
Use a hand-held hot-air soldering tool. Hakko and Pace are two suggested
sources. But there are many others. Once the operator aquires the skill,
it is much faster than trying to unsolder or solder a chip cap with a
standard solder iron. When soldering, if you solder one end first and
then the other, as the solder cools on the second termination it applies
a very large stress to the component. This can eventually lead to
cracks. Using a hot-air pencil allows you to solder both ends of the
termination at once, and this provides the same equilibrium of force as
the original reflow solder process.
Go to the AVX website for a lot of good information on pad geometry as
related to reliability. They also have a lot of good info on rework. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of - Bogert
Sent: Tuesday, November 22, 2005 4:27 AM
To: [log in to unmask]
Subject: [TN] Making existing PWB land areas larger

November 22, 2005

Folks we have an OEM who designed a PWB with too small a land area for
mounting a surface mount tantalum chip capacitor.  This design does not
allow for replacing the capacitor via manual soldering with an iron
since the part will be damaged if the iron touches the part body.  Is
there a way to enlarge the existing land size by some type of solder on
land piece.  I know they make such an item that folks use for
replacement of damaged traces.  If the lands can be increased in size,
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how does one do this and will a reliable solder connection result?

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