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Subject:
From:
"Jan Merstrand (EMW)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 30 Mar 2000 17:49:13 +0200
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text/plain
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text/plain (134 lines)
Bruce,
DBC stands for Direct Bonded Copper. It's a process where you plate Cu on substrates and often used in for example hightemp amp applications. 
Stellar Industries is one of many who make this..  http://www.stellarind.com/5metllz.html

Yes I know, the FET needs a very good thermal path and wire bond.
To solder the FET with Au/Sn requires high temperature, but if a substrate has combined ThickFilm (to which you mount components with Ag-epoxy) with DBC (to which you solder the FET) and want to replace the FET. That's a problem.
Our Ag-epoxy don't appreciate high temperatures and you can't avoid heating up the surrounding components, when trying to remove the FET, because of the the concept (TF & DBC). 
From there, I see two ways. Either replace the epoxy or replace the solder to one kind where the surrounding temperature, when removing FET, won't harm the Ag-epoxy. So, a low(-er) temperature solder around 160-200degC would be nice.
Any ideas? Anyone?

__________________________________________________
Jan Merstrand
Microwave MCM, Design/Production Support
Ericsson Microwave Systems AB. Defence Manufacturing
Office address: Bergfotsgatan 2, SE-431 84 Mölndal
Phone: +46 31 747 0725, Fax: +46 31 747 3515



> -----Original Message-----
> From: Misner, Bruce [mailto:[log in to unmask]]
> Sent: den 30 mars 2000 16:11
> To: [log in to unmask]
> Subject: Re: [TN] Solder at lower temperature
> 
> 
> Jan,
> 
> The FET requires 2 things: excellent thermal path and wire bonds. AuSn
> provides a thin interface with minimal voiding without flux 
> (although N2
> enviornment or blanket is required). This is good for both 
> requirements and
> hence has always been the material of choice in this 
> situation, especially
> for high rel applications (I see you are a Defense 
> contractor). It also has
> the added benefit of not leaching Au (because it already is 
> 80% Au) and
> allows additional processing of other areas of the assembly 
> at solder temps
> without reflowing the original interface. Unfortunately, I'm 
> not familar
> with acronim "DBC" for substrate (European vs American?).  If 
> you can better
> define this material I might be able to make other suggestions for FET
> attach.
> 
> One last note is that FETs can reach high delta T junction temp. This
> combined with the operating temp can bring the interface 
> dangerously in the
> range of typical solder (SN63) reflow temps.  Hope this helps.
> 
> Bruce Misner
> 
> > ----------
> > From:         Jan Merstrand 
> (EMW)[SMTP:[log in to unmask]]
> > Reply To:     TechNet E-Mail Forum.;Jan Merstrand (EMW)
> > Sent:         Thursday, March 30, 2000 4:11 AM
> > To:   [log in to unmask]
> > Subject:      [TN] Solder at lower temperature
> >
> > Hi guys and girls!!
> >
> > I have a question that I think many of you can answer.
> > Today we solder FET chips with Au/Sn solder onto a DBC 
> substrate with Au
> > surface.
> > The soldering area of the FET is Chromium/Nickel/Silver.
> >
> > I want to replace the Au/Sn solder with "something else".. 
> I don't want to
> > glue the chip to place, only solder.
> > The FET working temperature reaches up to 120degC.
> >
> > Any ideas on what kind of solder to use?
> > __________________________________________________
> > Jan Merstrand
> > Microwave MCM, Design/Production Support
> > Ericsson Microwave Systems AB. Defence Manufacturing
> > Office address: Bergfotsgatan 2, SE-431 84 Mölndal
> > Phone: +46 31 747 0725, Fax: +46 31 747 3515
> >
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