We don't offer the re-bake process on U800's any longer at Sphere (because Toru in Japan does not do it any longer). The actual root cause of the primary problem with U800 is as follows:
The modified DIP package has a very large heatsink pad, *bonding the chip to the pad is very difficult*, and it was a process that sometimes left the chip attached with essentially a cold solder joint, with high thermal resistance. This made the chip exhibit a range of problems as it warmed up. The re-bake process essentially re-seated the chip to the pad by re-flowing the attachment. *IF* the faults were related to this issue, the success rate was quite high.
The chip also had other stress failures not related to this specific issue, they cannot be cured by re-flowing the die attachment. Heatsinking the chip seems to help improve life, and I did it to any 24xx scope that I worked on. Even a 2" square of plate aluminum attached to the package makes a very big difference in package and die temperature.
This is not the only 24xx series ship to exhibit die attachment thermal problems, it also occurs in the 155-0236, and they have also been recovered by this process.
While I like the 24xx series operationally, the product did not age as well as earlier designs, and repairs and calibration often prove quite difficult after 30 years, especially if U800 is involved.
best regards,
walter
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Walter Shawlee 2
Sphere Research Corp. 3394 Sunnyside Rd.
West Kelowna, BC, V1Z 2V4 CANADA
Phone: +1 (250-769-1834 -:-
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