Inge,
I'm thinking of greater power cycle endurance for the Pb'ed version as opposed to the super 'hard' Au/Sn. To the best of my knowledge many power FETs are still attached with the high Pb solders to provide some ductility in the joint between the die and copper slug.
Si to alumina would present less CTE delta so would be more forgiving for either 'solder'
With the Pb'ed version you could possibly go to a Pd/Ag metallization, etc. Subject to your reliability constraints, thereby reducing substrate costs - maybe.
Cheaper since no gold would be involved in the solder.
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Thursday, October 09, 2008 3:09 PM
To: [log in to unmask]
Subject: Re: [TN] Need soldering advice ASAP No II
Right, they did not say that the solder liq is 400C, but that the max chip
temp is 400C. That makes sence. Question is what makes this formulae better
than AuSn? Do you have any idea? Better wetting or what? Cheaper, but
better?
Inge
----- Original Message -----
From: "Creswick, Steven" <[log in to unmask]>
To: "TechNet E-Mail Forum" <[log in to unmask]>; "Inge"
<[log in to unmask]>
Sent: Thursday, October 09, 2008 11:51 AM
Subject: RE: [TN] Need soldering advice ASAP No II
Inge,
I could be wrong but I thought that 92.5Pb/5Sn/2.5 Ag was 296°C Liq/289°C
Solidus. Assuming ~350°C peak, you ARE really pushing it too far for the
seal ring....
If you were using 90Pb/10Sn [302/275], or 95Pb/5 Sn [312/308], I don't see
that much difference.
Apparently, you are not using 90/10 or 95/5 ??
Steve :-)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Thursday, October 09, 2008 1:56 PM
To: [log in to unmask]
Subject: Re: [TN] Need soldering advice ASAP No II
I got an advice from IXYS's support. They recommend quite another solder for
their large power MOSFET 's :
92.5Pb/5Sn/2.5Ag. Has anyone of you used it?
Will increase the peak temperature from our today's +300C to +400C.
They ought to know. But that will melt the sealframe of the package,
because it's soldered with AuSn.
/Inge
----- Original Message -----
From: "Inge" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, October 09, 2008 10:41 AM
Subject: Re: [TN] Need soldering advice ASAP No II
> Thanks for the support of the linearing idea. I had a feeling that this
> could help.
> You make me think of placeing the connector on the boards before HASL.
> Hmmm...what will happen in the wave soldering of the boards later?
>
> You started the machinery in my old, gaggy brain....what about applying a
> solder mask right over? Is it realistic with that fine pitch? Will the
> solder ignore the solder mask and bridge?
>
> /Inge
>
>
> ----- Original Message -----
> From: "Thayer, Wayne" <[log in to unmask]>
> To: "TechNet E-Mail Forum" <[log in to unmask]>; "Inge"
> <[log in to unmask]>
> Sent: Thursday, October 09, 2008 10:19 AM
> Subject: RE: [TN] Need soldering advice ASAP No II
>
>
> Killing the protrusion should linearly improve the process. If you have
> cut them to negligible protrusion and still have trouble, then you are
> stuck with flux/temperature/time games, or some kind of hot air blow-off
> like out of the HASL machine.
>
> Wayne
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
> Sent: Thursday, October 09, 2008 12:31 PM
> To: [log in to unmask]
> Subject: Re: [TN] Need soldering advice ASAP No II
>
> Also need advice concerning soldering of a 120 pin, three row, right
> angle, through hole edge connector. The pitch is 1 mm, and the through
> hole copper collar is such, that the space between them is just a
> fraction of a millimeter. We tried to use our selective soldering
> machine, but whatever we do, the SnPb overbridges all the pins! I'm not
> surprised, because the solder surface tension will not allow the solder
> to withdraw pin by pin.
> However, such connectors are made and sold plenty of, so they must be
> solderable, question is with what. The selective soldering machine's
> 'wave pot' is 10 mm across and the minimum wave top is 3 mm. Does it
> help to cut the pins so that they are even with the board ? Today, the
> pins protrude
> 0.3 mms . Anyone who knows nothing?
> /Inge
> PS. Will send a photo to Dr Gregory.
>
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