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 ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. 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