damageheatintegrated-circuit
I tried to re-use a costly Integrated circuit which includes dual port ram inside.
I removed it from unused previous board by carefully using heat gun.
The problem is that the other part of the ram works fine, but the dual-port ram part always reads as 0x00. The interface is SPI and other part of the ASIC works just as fine, and the same firmware on the other board that was build from new IC works fine.
Is it possible that only that part of IC damaged from using heat?
From my experience with iron-based toner transfer you really need to apply lots of pressure to get the toner to transfer properly. I tried lots of different techniques (>10 tries) before finding the correct paper, correct/sufficient pressure across the board was important.
I suggest you try with an iron first and then move on to heat guns. I'm interested in your findings.
The temperature to which you set your temperature controlled heat-gun is about 100 degrees C higher than the recommended reflow profile for ceramic capacitors.
A normal vapor/air reflow profile looks more like this, where Peak Temperature is between 230-260C:
There is more information available in these documents:
Basically, you want to be careful to avoid thermal shock cracks, which occur when the part is heated too quickly. Move the heat gun in from a distance over the course of a minute rather than directly exposing it to 360C air.
Also, avoid heating the capacitor to much over 260 C for any length of time. This temperature is the general maximum for most parts, including silicon parts like the SOIC you replaced.
Best Answer
Yes. Manually using a heat gun (even a temperature controlled one) is a risky operation. The pins of an IC are designed to dissipate heat to the PCB so it is quite possible to have one side of your chip below the thermal failure tolerance while the other side is above that threshold, leading to potential damage to the silicon substrate in an isolated area.
Sounds like you got lucky in that you can see the damage straight-away rather than having an intermittent failure that might have only become apparent in the field.
There are products out there that make manual desoldering easier by dropping the melting point of your solder by forming a new alloy during desoldering. One such is ChipQuik but I have never used it myself for large chips. This makes it possible to melt all the solder simultaneously at a much lower temperature than normal (temps as low as 90 Celcius are possible, which is not likely to damage any IC I can think of).
(I don't work for the ChipQuik company by the way :))