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April 2009

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Subject:
From:
Guy Ramsey <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Guy Ramsey <[log in to unmask]>
Date:
Wed, 15 Apr 2009 11:11:09 -0400
Content-Type:
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text/plain (290 lines)
I think microns and micrometers are the same thing. 

http://en.wikipedia.org/wiki/Micron

Our board house considers 3 to 10 micro-inches to be gold flash, 50-150 is
heavy plate. 

3.8 micrometers is something like 150 micro-inches

 

From: [log in to unmask] [mailto:[log in to unmask]] 
Sent: Wednesday, April 15, 2009 8:49 AM
To: TechNet E-Mail Forum; Guy Ramsey
Cc: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

 


Hi Guy! I am metrically impaired - what is 3.8 micron in inches? Is your 3.8
micron referring to micrometers or nonSI units? (Given our recent SI units
discussion, my question is way too ironic!). 

Dave Hillman 
Rockwell Collins 
[log in to unmask] 





Guy Ramsey <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]> 

04/15/2009 07:37 AM 


Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Guy Ramsey <[log in to unmask]>


To

[log in to unmask] 


cc

	

Subject

Re: [TN] Gold/Tin Intermetallics, why are we afraid?

 

		




We build a lot of boards with electroplated gold finish, primarily for the
semiconductor test sector of our industry.

On one occasion we were populating little printed circuit wave guides with
SMT SMA shrouds. We noticed very poor solder appearance and very weak solder
connections. Some connections broke while attaching the cables. 

We determined that the gold plate was 3.8 micron. And judged the thickness
of the gold to be the cause of poor mechanical performance of the solder
connection. 

We replaced the boards with versions having about 0.3 micron gold plate. The
connections were much stronger. We were able to install all the cables, no
connection failures. To satisfy my own curiosity, I attempted to break one
of the connectors off the board. The solder connection did not fail. The
copper peeled off the board.

Thoughts? 

Guy

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Wednesday, April 15, 2009 2:42 AM
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

Thank you, George,
sometimes one needs kind of technical pragmatism.
Inge 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: tisdag 14 april 2009 23:41
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

I think both you and Vladimir are correct.  If the bond Ingemar,

I think both you and Vladimir are correct.  If the bond sits are room
temperature without any power cycling or mechanical stress it probably won't
degrade.  I assume Vladimir has seen the same kinds of failures I've seen
and there has always been a thermal and/or mechanical stress associated with
the failures.

Regards,
George
George M. Wenger
Andrew Wireless Solutions
Senior Principal FMA / Reliability Engineer 40 Technology Drive, Warren, NJ
07059
(908) 546-4531 [Office]  (732) 309-8964 [Cell] [log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Tuesday, April 14, 2009 5:15 PM
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

You mean that such a bond degrades even if just being in constant room
temperature and no power switching?
Inge


----- Original Message ----- 
From: <[log in to unmask]>
To: "TechNet E-Mail Forum" <[log in to unmask]>; "Inge" 
<[log in to unmask]>
Sent: Tuesday, April 14, 2009 11:07 PM
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?


> Hi Inge,
>
> Yes, the intermetallics itself is strong, BUT it doesn't count, as all

> failures I've seen goes at the tin/intermetallics interface. The
larger 
> were the platelets, the worse it looked.
>
> Regards,
>
> Vladimir
> ------Original Message------
> From: Inge
> Sender: TechNet
> To: [log in to unmask]
> ReplyTo: TechNet E-Mail Forum
> ReplyTo: Inge
> Sent: Apr 14, 2009 16:55
> Subject: [TN] Gold/Tin Intermetallics, why are we afraid?
>
> These infamous IMCs are like parias or ghosts in most people's mind in
our
> business. I shocked our production guys recently by giving the advice
to 
> let
> the boards go on. Large crystals and bad looking. But I always  try to

> avoid
> exaggerations. If no serious temp changes are predicted, nor any
severe
> power switching, why rework and risk introducing failures?  The actual
> components were very hard to rework, the cost had been unacceptable. I
can
> see many of you get  the coffee wrong. I don't mean to spread quality
> distractions, I talk about very few boards and a unique situation. My
> statement was based on the fact that a gold tin intermetallic bond is
> extremly strong and can last long, if not exposed to what I pointed at
> earlier. I expect to be hammered down in the shop floor until only the

> nose
> is visible....
>
> Inge
>
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