Mike,
You are correct about the minimal inerting required for the In, if using
flux.
For some reason, I was thinking of the Au/Sn with respect to the inerting
comment, even though I had essentially ruled the Au/Sn out.
Kindest regards,
Steve C
From: Inge Hernefjord [mailto:[log in to unmask]]
Sent: Sunday, March 31, 2013 4:14 PM
To: TechNet E-Mail Forum; Steven Creswick
Subject: Re: [TN] solder which does ot scavenge gold
Thanks Steve, formic acid it was. No, we could not handle them, but for our
MRSI cell II it was no problem. Its placement accuracy is +/- 5 microns!The
machine stands on pressurised air cushions, and a 1 ton granite block
absorbs vibrations that the cushions couldn't stop. In opposition to a
Panasonic chip shooter MRSI is slow, but fast enough.
On 31 March 2013 19:43, Steven Creswick <[log in to unmask]> wrote:
Formic acid?
.... and Mike thinks we couldn't handle 100 x 200 µm performs chuckle
chuckle. :-)
Ours was the medium vac model, down to about 70-80 mT...
http://www.sstinternational.com/prod_vacpres.html
Steve C
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
Sent: Sunday, March 31, 2013 1:35 PM
To: [log in to unmask]
Subject: Re: [TN] solder which does ot scavenge gold
Hi again,
this seems to be a never ending story. Well, I add some from our production
of GaAs and InGaAs MEMS like upcons. We found that the Indium oxidized very
fast for a number of alloys, so, after a lot of experimenting, we found the
best solution. We used a SSEC vacuum soldering machine, put the hundreds of
objects in the vacuum chamber, with 25 micrometers thick InSn preforms and a
small weight on them all. Then we sprayed a "cloud" of ant's acid (forgot
the chemical name) and put the cover on, vacuum pumped and soldered at +115C
for 15 minutes. Don't ask me why this and that, because I don't have all
details in mind. If I remember right, noble Mr In helped us..
There is a somewhat useful article about the process in Dropbox under
Soldering " Development of..Indium Soldering..."
Inge
On 31 March 2013 16:05, Mike Fenner <[log in to unmask]> wrote:
> Hmm
> Not sure there is much benefit from inerting at low temperature in
> presence of flux.
> Viability of performs against paste would depend on the volumes
> involved and geography of assembly.
> I see Guy talked about T5 paste. If T5 really is needed that implies a
> tiny dot size and implies a small perform also which might give
> supplier issues and handling issues in use.
> Personally I would recheck the T5 requirement on the one hand and
> availability on the other. [This to make sure it isn't a "price book"
> quote].
> Possibly other solder processes might be possible.
> So far as non solder attached is concerned:
> H20E is OK, but like Steve I prefer 84-1 series more, I step back to
> take notes on wire bonding etc.
>
> Best Wishes
>
>
>
> Mike
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
> Sent: Sunday, March 31, 2013 11:43 AM
> To: [log in to unmask]
> Subject: Re: [TN] solder which does ot scavenge gold
>
> Guy,
>
> A couple of additional thoughts for you.
>
> Instead of paste, consider the use of performs. Like Mike says, flux
> will be a challenge. Definitely use inerting and possibly a localized
> reflow apparatus that provides a very good localized reflow
> atmosphere. The low temp of the proposed IN alloy, and the high temp
> of the Au/Sn will definitely introduce speedbumps in a nice process flow.
>
> If your substrate were LTCC or 96-99% alumina the CTE of the GaAs
> would be almost a perfect match [3-7, 6-7, and 6-7 PPM/°C
> respectively]. The slickest thing to do with LTCC is create a pocket
> to drop the diode in [face up] and use no-loop ribbon bonds to bond
> from diode to substrate using 0.5 x
> 2 or 4 mil Au ribbon. Bonding would readily be performed below your max
> allowable temp limits.
>
> Since most adhesives do not bond well to gold or solder, the potential
> for CTE mis-match in your system [and subsequent bad connections]
> would seem to require a thorough examination.
>
> If you could use ENEPIG for a surface finish, you could
> non-conductively bond the diode, face up, and wire, or ribbon, bond
> the diode to the circuit.
> Can you get away with it from a frequency response/circuit function
> point of view? This still presents issues from a process flow point
> of view, but seems to be the cleanest approach to a hybrid guy. That
> or bumping...
>
> A blessed Easter to all.
>
> Steve C
>
>
> -----Original Message-----
> From: Steven Creswick [mailto:[log in to unmask]]
> Sent: Friday, March 29, 2013 10:57 AM
> To: 'TechNet E-Mail Forum'; 'Guy Ramsey'
> Subject: RE: [TN] solder which does ot scavenge gold
>
> Guy,
>
> Others likely have already touched on this but the Indalloy #2 has a
> 154°C liquidus which meets your temp limitations. 80/20 Au/Sn is a
> 280°C eutectic which will not meet your temp limitations.
>
> I suspect that 80/20 will be just as expensive as the #2.
>
> Don't know what you substrate/board is, but it will likely not take
> kindly to the temps required of 80/20 either.
>
> I view a conductive adhesive as being THE last thing I would do.
> Instead or H20E, I would definitely steer you to Ablebond 84-1
> [anything in the 84-1LMI, LMINB1, etc series]. Much better thermal
> characteristics! But getting any adhesive to adhere to gold is
> problematic! ANY amount of substrate/board flex, and the die will pop
> right off.
>
> Generic silver glasses have too high a cure temp as well.
>
> You could thermosonically flip chip bond this low I/O device to the
> board if you could bump either the diode or the board. Simply
> requires one or two gold ball bonds [to form the bumps] on each diode
> [or substrate/board pad].
> The Au/Au bond will form nicely at 150°C + ultrasonics and about 35-50
> gms of force per 'bump'. Alas, you require a bondable board and a $250K
> bonder... Au/Au thermocompression could work to, but temps will be way
> too
> high. Additionally, the face of the diode will standoff the
> substrate/board by 25-50 µm, depending on wire size used, and actual
> bumping process.
>
> I don't like working with high Indiums either, but don't see an
> immediate alternative.
>
>
> Steve Creswick
> Sr Associate - Balanced Enterprise Solutions
> http://www.linkedin.com/in/stevencreswick
> 616 834 1883 <tel:616%20834%201883>
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
> Sent: Friday, March 29, 2013 9:28 AM
> To: [log in to unmask]
> Subject: [TN] solder which does ot scavenge gold
>
> Background info:
> We were asked to populate and assembly with a Ma-Com part, MA46H120, a
> GaAs Constant Gamma Flip-Chip Varactor Diode. The data sheet says:
>
> Mounting Techniques - These chips were designed to be inserted onto
> hard or soft substrates with the junction side down. They can be
> mounted with conductive epoxy or with a low temperature solder
> preform. The die can also be assembled with the junction side up, and
> wire or ribbon bonds made to the pads.
>
> Solder Die Attachment - Solder which does not scavenge gold, such as
> Indalloy #2 (80In-15Pb-5Ag) is recommended. Sn-Pb based solders are
> not recommended due to solder Embrittlement. Do not expose die to a
> temperature greater than 235C, or greater than 200C for longer than 10
> seconds.
>
> The Indalloy #2 cost $2,222.00 for 100gm or type five solder paste.
>
> We now have another customer asking for us to solder to thick gold.
> They don't have a low temp requirement and asked for SnAu solder
> (Indalloy #182) 80Au-20Sn. . . I shudder to think what that will cost,
> and I don't think the part, an inductor, will survive the 300C reflow.
>
> Question:
> Does SAC 305 "scavenge gold"? Would it form a brittle solder
> connection on a thick soft gold pad?
>
> Guy
>
>
>
>
>
>
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