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
>
>
>
> -----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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