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April 2009

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Subject:
From:
Werner Engelmaier /* <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 15 Apr 2009 16:13:36 -0400
Content-Type:
text/plain
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text/plain (548 lines)
 Hi Vladimir,
As Dave points out, if specs are followed, there should be no issues with either 'Ag-embrittlement'; or 'Au-embrittlement.'
Of course, the issue was never immersion-anything, but electroplating either Au or Ag.

Werner


 


 

-----Original Message-----
From: David D. Hillman <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, 15 Apr 2009 2:49 pm
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?










Hi Vlad - yes, the reliability investigation report by the IPC 4-14 
committee is complete.  Go to the IPC website and search for technical 
paper IPC-TR-586 which contains the investigation information/details. The 
Reader's Digest version is: as the silver content of a solder joint 
increases, there is a corresponding decrease in solder joint thermal cycle 
reliability - BUT - a solder joint can accommodate much more silver in 
comparison to gold. If the IPC-4553 Immersion Silver pwb finish 
specification is followed, there should not be an issue with "silver 
embrittlement".

Dave



Vladimir Igoshev <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
04/15/2009 12:37 PM
Please respond to
[log in to unmask]


To
[log in to unmask]
cc

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






Werner,

We've been through it and not just once. I wish I could have those samples 
to look at, as I've never seen anything like "Ag-embrittlement". Please 
correct me if I'm wrong but a couple of months ago Dave H. "spelled out" a 
final verdict of an IPC committee on the issue.

Regards,

Vladimir
SENTEC
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca


-----Original Message-----
From: Werner Engelmaier /* <[log in to unmask]>

Date:         Wed, 15 Apr 2009 13:19:34 
To: <[log in to unmask]>
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?


 Vladimir,
Oh yes, there is 'Ag-embrittlement'?it just never reached the same level 
of notoriety as 'Au-embrittlement.' The whole 5-year effort of the IEEE 
Compliant Lead Task Force (CLTF) was started by  'Ag-embrittlement' when 
TI started production in Singapore and their J-leads were Ag-plated. It 
all hit the fan when the first customer, IBM in Austin, had PLCCs dropping 
off the PWBs on bed-of-nail testing.

Werner


 


 

-----Original Message-----
From: [log in to unmask]
To: TechNet E-Mail Forum <[log in to unmask]>; [log in to unmask]
Sent: Wed, 15 Apr 2009 12:41 pm
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?










Werner,

I would say that Ag-Sn platelets do the same thing to solder joints as 
Au-Sn. 
There is no "Ag embrittlement". :-)

Vladimir
SENTEC
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca


-----Original Message-----
From: Werner Engelmaier /* <[log in to unmask]>

Date:         Wed, 15 Apr 2009 11:45:28 
To: <[log in to unmask]>
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?


 Vladimir is correct.
"Gold-embrittlement" is the weakening of the SJ structure by too many weak 

interfaces with the crystalline AuSn-IMC platelets and the solder. The 
more such 
IMC [AgSn-IMCs do exactly the same] platelets results in higher density of 
such 
interfaces and an increased SJ weakness.
The dull, grainy, lumpy appearance stems from these IMC-platelets pocking 
through the SJ surface.

Werner0A 

 


 

-----Original Message-----
From: Vladimir Igoshev <[log in to unmask]>
To: [log in to unmask]
Sent: Wed, 15 Apr 2009 11:29 am
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?










Because you had different materials at the interface. With thick Au your 
joints 
had a relatively wide band of "weak connection" at the Au/Sn-Sn interface.

Regards,

Vladimir
SENTEC
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca


-----Original Message-----
From: Guy Ramsey <[log in to unmask]>

Date:         Wed, 15 Apr 2009 11:19:59 
To: <[log in to unmask]>
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?


The point is the connections made on thick gold were substantially weaker
than those made to nickel though thin gold. 

I don't know if there was nickel in the weak connections. But, they were
dull, grainy, lumpy and weak, compared to the connections made through 
thin
gold. 

Guy

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir Igoshev
Sent: Wednesday, April 15, 2009 8:45 AM
To: [log in to unmask]
Subject: Re: [TN] Gold/Tin Intermetallics, why are we afraid?

It just tells you had good solder joints. In many cases laminate (board)
breaks when a load is applied to properly formed solder joints.

Regards,

Vladimir
SENTEC
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca


-----Original Message-----
From: Guy Ramsey <gramse
[log in to unmask]>

Date:         Wed, 15 Apr 2009 08:37:31 
To: <[log in to unmask]>
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 are20correct.  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 I
ntermetallics, 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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>
>
>
> SENTEC
> 11 Canadian Road, Unit 7.
> Scarborough, ON M1R 5G1
> Tel: (416) 899-1882
> Fax: (905) 882-8812
> www.sentec.ca
> 

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