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March 2013

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Subject:
From:
Inge Hernefjord <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Inge Hernefjord <[log in to unmask]>
Date:
Sun, 31 Mar 2013 22:13:45 +0200
Content-Type:
text/plain
Parts/Attachments:
text/plain (236 lines)
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
> >
> >
> >
> > -----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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