On Monday 18 January 2010 19:30:55 Gabriel Paubert wrote: > On Mon, Jan 18, 2010 at 06:26:41PM -0500, Mark Stanley wrote: > > What kind of problems are you having? > > a) That I am a beginner with this technique. > > b) That I don't (yet) have the right tools to handle the dies, that > are small (square 15mil/side). They are ordered and should be > here early next month. I end up with either not enough epoxy > or too much with the die drowned in epoxy.
I use a ball pick for applying the epoxy. The pick is normally used for cleaning the ball wedge on the bonding machine and appears to be almost molecular sharp. I mount it in the handle of one of those small screw drivers used for repairing glasses. I can apply a very precise amount of epoxy. Oh yeah, and a microscope *really* helps when applying the epoxy. ;) > c) That I still have to order the proper epoxy (the one I bought from > Farnell has a pot life of 10 minutes, which is annoyingly short). The stuff I use can sit on my workbench at least half a day before it starts clumping. > d) That the components are germanium based, therefore very sensitive to > temperature and I cannot use epoxies with cure temperatures above 125°C. What I use can cure at temperatures as low as 50°C but will cure in 10 minutes at 100°C. > e) That the distributors in Spain take outrageous margins ($200 becomes > €400), so I'm trying to find a cheap way to get the epoxy. That's pretty rough. Are you able to order from over seas companies? > This may indicate that the gluing was not perfect (to put it mildly). The > die is small so the force to remove it is rather small too. I've had to use enough force during removal that I've dented the metal substrate. > Besides that heating above Tg of the epoxy helps: True. Except that the brand I use releases at temperatures too high for the other dies on my modules so I generally remove the bad die by hand. > What epoxy did you use (manufacturer and reference)? I'll get you the information tomorrow when I get back to work. For long term storage we keep it packed with dry ice (CO2) in the freezer and store the in- service tube in the refrigerator. We've had in-service tubes last up to six months. > I've spent quite some time trying to find the best epoxy for my application > over the last two weeks but am still undecided. Actually I was considering > either Epotek H20E which seems to be an industry workhorse, or > Alfaadhesives' E10-110 because of the convenience of the pouches (combined > with high Tg and low cure temperature although the cure schedule is > strange). I think the stuff I use might be a bit expensive. However, I only squeeze out a 4mm drop and can keep it on my workbench for several hours while I am building modules. With that one drop I can build 3 or 4 modules, each one having a VVA, 2 amplifier dies, a diode, 2 hand wound inductors, and around 10 or 12 resistors and capacitors. It cures at temperatures well below the limits of the dies and the only trade-off is that lower temperatures take a lot longer to cure. Mark Stanley _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
