Shelf life of tin electroplate

Letter 5659

Shelf life of tin electroplate

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I have a customer who is specifying Tin coated olin 638 1/4 hard, electro-plate Tin 1.02-2.54 microns (98-100%Sn, .5%Pb MAX) over a copper barrier 1.78 microns minimum. They have had solderability problems in the past, they think due to shelf life. I am not a plater, but I purchase and use a great deal of plated products. The questions I have..

1. Is there sufficient plating to provide good solderability?

2. What is the shelf life of the plated product before it looses solderability?

3. These parts will have plastic squirted around them, does this significantly shorten a shelf life? Thanks for your help!

Dirk Huff
- Elgin Il, USA

First of two simultaneous responses -- .

1. Yes, that is enough for solderability.

2. Yes there is a shelf life for "pure " solder. This will vary by storage conditions, packaging, and impurities in the solder, probably organics, as well as time. Bright tin does not solder any where near as well as matte tin does, but some ------- specify bright tin because it "looks better", and then bitch. Parts that are treated with a stearic acid and xylene mixture have a lot longer shelf life.

3. The plastic is not going to help the situation and will vary by the type of plastic.

Typical shelf life is from 6 weeks to 6 months. A good reason for just in time deliveries with a pad to make sure that there are some on the shelf and mandate first in- first out use.

James Watts
- Navarre, Florida

Second of two simultaneous responses -- .

Hi Dirk ,

Yes the deposits are too thin for good shelf life for solderability , the Barrier layer of copper is too thin and probably poorly chosen , copper will migrate into tin to give a bronze , a barrier layer of Nickel is more usual and its minimum thickness is to be 5 microns ( so plate for 7.5 microns ) for good solderability an absolute minimum of 2 microns is needed but more usually 5 microns .

Be aware that tin readily oxidises and needs either to be soldered right away ( usually within the same day , but could streatch to 2 days ) or treated to prevent oxidation. The longer the tin is left on the shelf before soldering , the more agressive needs to be the Flux you use Hope this is of some help

regards

John Tenison - Woods
- Victoria Australia

August 6, 2009

I have facing of the problem that customer asking for the shelf life for tin dipped and plated terminal. Customer kept the transformer over a year and found poor solder during the wave solder assembly process.
1. Can help to provide what is the actual shelf life for tin dipping terminal and plated termninal warranty period (shelf life).

2. waht is the environment aspect will affect the thin dipped ot plated surface?

Thanks,
Yuu GS

Yuu Guan Seng
IncoilsTransformer Maker - Butterworth,Penang,Malaysia

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