Brian,

There are a couple of reasons why you might tin parts:

- the leads are gold so you tin them to improve solderability

- the parts are old and/or have not been stored properly so you tin them to
improve solderability

HOWEVER, we had a board for which we were tinning parts because the leads
looked discolored, implying poor solderability.  I gradually showed that
this was unnecessary - we would get good solder joints without tinning the
parts.  I would suggest trying not tinning one part on several boards of one
design first to see what results and then gradually increasing the quantity
and variety of parts.  Don't tell the quality inspector which parts were not
tinned - you don't want to introduce any bias into the results.

The result was equal quality, lower cost and shorter cycle time due to
eliminating an unnecessary operation.

Good luck.

-Steve


Steven K. Lustig
Process Engineer
EMS Technologies, Inc.
Norcross, GA
(770) 263-9200 x4714
[log in to unmask]


-----Original Message-----
From: [log in to unmask]
[mailto:[log in to unmask]]
Sent: Monday, January 17, 2000 7:27 AM
To: [log in to unmask]
Subject: [TN] Pin Pre-Tinning


Hello T'-Netters,
An assembly engineer just asked a question which sparked some curiosity.
"Why do
we pre-tin all of our pins/cotacts prior to installation". The majority of
the
responses were: "That's the way we've always done it". Is there some
mechanical/metallurgical or manufacturing benefit from pre-tinning
pins/connectors prior to installation and subsequent hand/wave soldering?
Could
someone explain the pros and cons of pre-tinning? And lastly, are there
particular manufacturing specifications (examples please) which require the
pins
to be pre-tinned.

Obviously there are benefits, otherwise vendors wouldn't provide this
option.
I'd just like to get some opinions.


Thanks.

Brian Guidi
Teledyne Electronic Technologies
Printed Circuit Technology

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