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.
Werner
-----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 <[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 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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>
>
>
> 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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