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June 2006

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Subject:
From:
"Barmuta, Mike" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Barmuta, Mike
Date:
Wed, 21 Jun 2006 09:19:33 -0700
Content-Type:
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text/plain (205 lines)
Ioan: The organics are part of the make up of the tin plating bath. The "bright tin" plating baths have higher concentrations of organics to create a smaller plated grain structure thus producing a brighter i.e. more reflective surface. A matte tin bath has less additives creating a larger/coarser plating deposit giving the matte appearance.

However it is just not the initial organic additives that is the problem. I don't know what type of tin bath the supplier is using but let me give you an example:

A sulfuric based tin stannous sulfate type bath is be able to produce acceptable parts when new. Most of these baths use a multiple organic additive system, such as a Schlotter bath or a variation of. 
 
These organics are consumed and broken down at different rates.  As the bath ages it will build a variety of organic constituents. Some beneficial some not.  Also the stannous tin (Sn2) will oxidize and start to form stannic tin (Sn4). The stannous oxide in this state is unfilterable and insoluble in the sulfuric acid.
 
Both the organics from excessive additives and/or their breakdown by-products along with stannic tin can cause solderability problems.
 
It is very critical for the successful long term quality of  component solderability that the bath is monitored and maintained to control the additives and organic/inorganic by-products. It is absolutely necessary to have the correct analytical and control procedures in place to maintain bath performance. 
Such things as control of brightener and organic build-up whether by Hull cell or more sophisticated instrumental analysis, establishing carbon treatment frequencies and procedures for the bath, precipitation and removal of stannic tin, analysis of codeposited organics in the tin plate, etc.

I would recommend working with your component supplier and using a matte and/or semi-matte plating finish. You can also specify the amount of allowable organics in the deposit as a percentage of carbon found in the deposit.

                                                                                Regards
                                                                                                Michael Barmuta
                                                                                                Staff Engineer
                                                                                                Fluke Corp.
                                                                                                Everett WA
                                                                                                425-446-6076
                                                                                	
  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of R Sedlak
Sent: Wednesday, June 21, 2006 8:33 AM
To: [log in to unmask]
Subject: Re: [TN] Blowholes pandemic

Organics are common to most electroplating baths, as they are used as brighteners/levelers, or in other words, additives to improve and make the plating more uniform....

Problem is they decompose, and every so often need to be removed, by a process called "carbon treating".  This process is long, involved, and interferes with production, thus is easily put off, if the plating looks good...

No way I know to test the plating for excess organics, other than by doing effectively what you are doing, melting it, and checking for blowholes.

Maybe Mike has a better idea....   I think of him as "Mr. Plating".

Rudy Sedlak

"Tempea, Ioan" <[log in to unmask]> wrote: Thanks Mike and Rudy!

I will change my question to: what on Earth are the organics doing in the plating? Is this normal?

Any suggestions on how to control the AVL or the Incoming inspection of these parts to avoid the issue?

Thanks,

Ioan

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of R Sedlak
Sent: Wednesday, June 21, 2006 11:12 AM
To: [log in to unmask]
Subject: Re: [TN] Blowholes pandemic


I will go farther, and suggest that Mike is almost certainly correct, this being the source of most "blowholes".

Rudy Sedlak

"Barmuta, Mike"  wrote: Ioan: The blowholes you are seeing could be the result of organics in
the tin plating outgassing during reflow. When heated they release CO
and CO2 gases creating voids.


Regards

Michael Barmuta

Staff Engineer

Fluke Corp.

Everett WA

425-446-6076

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tempea, Ioan
Sent: Wednesday, June 21, 2006 5:57 AM
To: [log in to unmask]
Subject: [TN] Blowholes pandemic

Hi Technos,

for a couple of days I see occurences of blowholes in the joints of,
guess what, SMT 0603 resistors.

The reflow recipe did not change and we're talking about 2 different
established products, we have run many of each before. One is WS, the
other one no-clean. Each one uses different brand of solder paste, SnPb.

I have changed the paste with fresh one, no positive results. I have
changed the reels with different date codes, Bingo! But even the "bad"
parts were quite fresh, less than one year old. One of them is pure Sn
plated, don't know about the other ones.

The question is: where on Earth can humidity stay in a ceramic resistor?
What else can be the cause of the blowholes? Did not bake the boards,
since changing the components worked, so I guess the PCBs are out of the
hook...

Thanks,

Ioan

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