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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 19:37:12 +0200
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text/plain (229 lines)
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..."


On 31 March 2013 19:34, Inge Hernefjord <[log in to unmask]> wrote:

> 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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>
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