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March 2008

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Subject:
From:
Anil Kher <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Anil Kher <[log in to unmask]>
Date:
Sun, 2 Mar 2008 12:06:10 +0530
Content-Type:
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text/plain (139 lines)
 stopped doing acid tin years ago. Rememeber that over period stannic tin
builds up in the bath. Co deposits and creates problem. Used to cover the
bath surface with ellipsoidal shaped floaters - not balls as they spin and
increase surface to oxidation.

Analyse the bath fr stannic tin & ppt the insolubles by using sedimentation
additive and decant. Chk it out

Anil

-----Original Message-----
From: Ido Mashall [mailto:[log in to unmask]] 
Sent: Sunday, March 02, 2008 12:27 AM
Subject: Re: acid tin plating question

Hi Adam

I suggest you should check your photo/developing stage too.
Sometimes you are getting photoresist residues on the copper surface making
it hard for the Tin to form on the surface and sometimes it form loosely and
etched in the etcher.

Ido Mashall

www.beyond-materials.com

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Adam Seychell
Sent: Saturday, March 01, 2008 1:53 AM
To: [log in to unmask]
Subject: Re: [TN] acid tin plating question

It looks very close to those photos, except most of the pits are near inner
ring of the pads. There is also pitting near the some straight edges. It
appears low current density areas are most susceptible. Many smaller pits
are not completely etched through, leaving the underlying copper visible.
Unfortunately I don't have a digital microscope to send you photos.
Are those photos taken after solder reflowing the boards ?

Adam Seychell.

Steve Gregory wrote:
> Hi Adam!
> 
> Do any of the holes look like this:
> 
> http://stevezeva.homestead.com/AnnularRing3.jpg
> 
>  
> http://stevezeva.homestead.com/AnnularRing.jpg
> 
> http://stevezeva.homestead.com/AnnularRing2.jpg
> 
> Steve Gregory
> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Adam Seychell
> Sent: Friday, February 29, 2008 5:03 AM
> To: [log in to unmask]
> Subject: [TN] acid tin plating question
> 
> Hi all.
> I'm trying to solve a problem of pitting around the holes after 
> ammoniacal etching. I suspect my problem is insufficient deposits of 
> electroplated tin resist around the holes, which is making it more 
> susceptible to attack by the etchant. The reason I think its a tin 
> problem is because prior to etching, the tin deposits appear solid and 
> smooth when viewed under a microscope. However after etching there is 
> evidence of pitting around many holes.
> The problem seems to go away with excessive plating, about 8um or more. 
> Normally I've not had a problem at only 2~3um.
> 
> Also is it normal to have a small amount of white foaming hydrogen gas 
> above the PCB while tin plating ? The tin bath is an acid stannous 
> sulfate type with brighteners, and has always been a milky yellow 
> appearance.
> 
> 
> Adam Seychell
> 
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