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TECHNET  July 2008

TECHNET July 2008

Subject:

Re: Immersion Tin Problem

From:

Inge <[log in to unmask]>

Reply-To:

TechNet E-Mail Forum <[log in to unmask]>, Inge <[log in to unmask]>

Date:

Wed, 9 Jul 2008 11:51:11 -0700

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (194 lines)

I've said it before, and I say it now :  there is no problem less board 
finish!  With a less knowhowant supplier, any plating process can 
murphyrize. We have shipped millions of ENIG boards, and with success. How 
come?  We have a Baretta against the supplier's head, day and night, or even 
worse: one of our Qs, with Juran's bible well visible in the black belt. 
It's the mutual enthusiasmus that makes it. If your company got still one of 
those oldtimer chemists who stinks of glue and solvents and who has his 
office crowded with test samples and the book shelves squeeking under the 
weight of hundreds of books in alchemy, then treat him like a precious gift! 
These are the guys who save millions for you and makes the wheels running. 
And...if you don't  see a PhD title on his badge, don't worry...the white 
coated man in front of you, gray haired and with glasses from the 60's on 
his nose,  he frownes at titles and points at the time when a 'simple' 
engineer education was at a level that could make any modern student faint. 
I've heard stories from big companies, where these characters were regarded 
as overhead costs (or they used other terms), and they were more or less 
kicked out when the economists 'saved money' for the owners. After that, the 
wheels stopped for longer times, which cost magnitudes more than the old 
chemist.

Inge



----- Original Message ----- 
From: "Guy Ramsey" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, July 08, 2008 12:49 PM
Subject: Re: [TN] Immersion Tin Problem


> ENIG has its own set of problems. I prefer immersion silver. You still 
> have
> to be careful not nearly as careful.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Dale Ritzen
> Sent: Monday, July 07, 2008 8:21 AM
> To: [log in to unmask]
> Subject: Re: [TN] Immersion Tin Problem
>
> Rex et al,
> We have had the same problem with white immersion tin finishes. They are 
> to
> be avoided if you can talk your customer into something else. We are
> currently in the process of talking with our white tin customer about an
> ENIG PCB finish.
>
> However, if you MUST use them, there are some reflow profiling changes 
> that
> you can use to successfully do this most of the time (and they will make
> your process guys go bonkers). They mostly concern running at the lowest 
> end
> of your Pb-free reflow temperatures (read: so you get MOST of the solder
> paste "BB's" to flow) and praying that the copper-tin mix on the exposed
> side doesn't start changing chemically before you reflow it. We have found
> that minimizing the heated, non-soldered surface exposure to oxygen does
> help a lot (i.e. nitrogen atmosphere during 1st and 2nd reflow). Plus, we
> store the boards that have completed the SMT process in a nitrogen cabinet
> between the SMT and PTH steps of the build. This does slow down the
> oxidizing effect on the surface of the tin, but it is not the final answer
> since it does nothing to stop the creation of Tin/Copper intermetallic 
> under
> heat. Yes, all this extra handling/process control raises the price of the
> completed assembly significantly.
>
> The most effective process is to use brand new boards (no shelf life), 
> speed
> the product through any/all processes it needs to go through at the lowest
> temperatures possible (that is tough with Pb-free solders), and minimize
> exposure to oxygen until the product is finished goods. Actually, the 
> final
> solution is to avoid immersion tin like the Black Plague...
>
> Dale Ritzen, CQA
> Quality Manager/ISO Management Representative Austin Manufacturing 
> Services
>
>
> -----Original Message-----
> From: Rex Waygood [mailto:[log in to unmask]]
> Sent: Friday, July 04, 2008 4:35 AM
> To: [log in to unmask]
> Subject: [TN] Immersion Tin Problem
>
> 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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