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May 2008

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Subject:
From:
John Burke <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, John Burke <[log in to unmask]>
Date:
Tue, 13 May 2008 11:43:19 -0700
Content-Type:
text/plain
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text/plain (244 lines)
Here is my theory:

The following is assumed : The leadframe is a nickel / Iron alloy such as
alloy 42 both of which are magnetic.

Theory is as follows:

The small stainless particles are being introduced at one of the following
points:

1	During component "touch up" being transferred from an iron bit
cleaned with a stainless magnetic grade material
2	During a fluid based cleaning process where the fluid has been
contaminated by cleaning something else which perhaps was "rough cleaned"
using a wire wool?
3	Contaminated airflow caused by?????

 
 
John Burke
 
(408) 515 4992

-----Original Message-----
From: Leland Woodall [mailto:[log in to unmask]] 
Sent: Tuesday, May 13, 2008 11:23 AM
To: TechNet E-Mail Forum; John Burke
Subject: RE: [TN] Stainless Steel Contamination Question

John,

We've never performed a test for magnetic properties.  I'll see if we
can salvage a sample from those we've shot on our SEM.

That may at least tell us something new!

Thanks,

Leland

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Burke
Sent: Tuesday, May 13, 2008 1:58 PM
To: [log in to unmask]
Subject: Re: [TN] Stainless Steel Contamination Question

It is probably  a magnetic grade of stainless if it is clinging to the
leads, can you confirm this?

 
 
John Burke
 
(408) 515 4992

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Tuesday, May 13, 2008 8:06 AM
To: [log in to unmask]
Subject: Re: [TN] Stainless Steel Contamination Question

David,

We haven't seen any of this interfering with or preventing a solder
joint from forming.  In every instance, it's clinging to the leads.

Wouldn't that pretty much rule out our reflow ovens?

The earliest part of our process where this has been found is at
in-circuit test after the wave solder operation.

That leaves our Omron AOIs, our Huntron visioning stations, and our
flying probe machines.  We've looked in and all around those processes,
and still are coming up with nothing.

Like trying to find a (stainless steel) needle in a haystack...

Leland

-----Original Message-----
From: David Greig [mailto:[log in to unmask]] 
Sent: Tuesday, May 13, 2008 10:57 AM
To: Leland Woodall
Subject: RE: [TN] Stainless Steel Contamination Question

Are the fibres causing any problems with solder joint formation, if so
then trace backwards from the oven. If not then look
around the oven and forwards to the point at which they are observed.
What about the air/nitrogen source into the oven? Any bit
of kit that is opened and closed regularly.

The gaskets are used likely on electronic or even electrics enclosures,
particularly clam shell cases. The cut ends of the
gaskets typically do fray out loose fibres.


Best Regards
 
David Greig

-----Original Message-----
From: Leland Woodall [mailto:[log in to unmask]] 
Sent: 13 May 2008 15:29
To: David Greig
Subject: RE: [TN] Stainless Steel Contamination Question

David,

Where in my manufacturing process might I find one of the knitted EMC
gaskets?  Are you familiar with any particular machinery
that would use these?

Thanks again,

Leland

-----Original Message-----
From: David Greig [mailto:[log in to unmask]]
Sent: Tuesday, May 13, 2008 10:26 AM
To: 'TechNet E-Mail Forum'; Leland Woodall
Subject: RE: [TN] Stainless Steel Contamination Question

Perhaps an EMC gasket. One of the knitted mesh materials commonly used
consists of knitted stainless steel fabric. There may
well be residues of silicones and other lubricates used in the knitting
or weaving.


Best Regards
 
David Greig

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: 13 May 2008 14:47
To: [log in to unmask]
Subject: [TN] Stainless Steel Contamination Question
Importance: High

Hi Everyone,

 

We've had a problem lately with fine strands of stainless steel wire
being found on top of some of our .5 mm pitch ICs.  This
has caused both internal and external issues, and we've yet to identify
the source.

 

It's definitely formed wire, with a thickness ranging from 7 to 10
microns, and up to 3 mm in length.  

 

Our automated optical inspection stations can only reliably detect
widths of 12 to 15 microns.

 

I've checked the internet in an attempt to find common applications of
this wire.  I've found two, and they were for ultra-fine
filters and stencil screen mesh.  We've investigated (I think) all of
our machinery that would utilize filters this small and
have found no such usage.
I've also checked every stencil in our plant, and all of our mesh
material is some type of a plastic compound.

 

Do you have any idea where this stainless steel might be coming from?

 

Any suggestions would be sincerely appreciated!

 

Thanks,

 

Leland


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