Great! Wonderful! So with RoHS (Risk of Halting Soldering) you can at least 
solder once. What a hit!

Inge



----- Original Message ----- 
From: "R Sedlak" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, July 04, 2008 5:27 PM
Subject: Re: [TN] Immersion Tin Problem


> All of this makes perfect sense if you consider the mechanisms.
>
> ImSn has a shelf life, which is controlled by the spontaneous formation of 
> the Tin/Copper intermetallic, which begins to form as the Tin is plated at 
> the interface.   When the Tin has totally converted to the Tin/Copper 
> intermetallic, it can no longer be soldered.
>
> Heat accelerates the formation of the intermetallic.
>
> Your first pass is accelerating the formation of the intermetallic 
> dramatically.   You are likely simply converting the whole of the ImSn to 
> intermetallic, and it is game over.
>
> Rudy Sedlak
> RD Chemical Company
>
>
> --- On Fri, 7/4/08, Rex Waygood <[log in to unmask]> wrote:
>
>> From: Rex Waygood <[log in to unmask]>
>> Subject: [TN] Immersion Tin Problem
>> To: [log in to unmask]
>> Date: Friday, July 4, 2008, 2:35 AM
>> We do not usually use Immersion Tin finish boards but we
>> have some with
>> a problem.
>> The boards are about 10-12 weeks old, stored in original
>> packing, double
>> sided PTH and lead free processed.
>> Side 1 processed OK
>> Side 2 had some non-wet problems (Profiles and dwells etc
>> are industry
>> 'norm')
>> Hand soldering has proved to be nigh on impossible.
>> The immersion tin is within the thickness specified
>> (typical values 1.1
>> to 1.2 micron)
>>
>> Should we have avoided ImSn (as we have done previously)?
>>
>> Is the spec for the ImSn OK?
>>
>> Has the PCB mfr done something wrong?
>>
>> Have we? (apart from accepting ImSn)
>>
>> Rex
>>
>>
>> Rex Waygood
>> Technical Manager
>>
>> PartnerTech Poole Ltd
>> Benson Road
>> Poole
>> Dorset BH17 0RY
>> United Kingdom
>>
>> Tel: +44 (0)1202 674333
>> Fax: +44 (0)1202 678028
>> DDI: +44 (0)1202 338222
>> Mob: +44 (0)7887 997403
>>
>> [log in to unmask]
>> www.PartnerTech.co.uk
>>
>>
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