Replacement of an old MOSFET

Old defect MOSFET was not easy avialable in such a package - replacment method smt for tht

ready to mount
N-Channel MOSFET, defect caused by applying a wrong polarity, silicon internal melted, broken package. Drain-Source zero ohms. Plastic of the broken MOSFET removed in a vice. Die removed with a sharp screwdriver. A new SMT MOSFET will be soldered on the heatsink of the old MOSFET.
For comparison: Left side the photo shows another MOSFET with and without package.
SMT power MOSFET soldered on the heatsink with a hot-air-gun. The gate required a small piece of a epoxy PCB as holder. Source is the wire showing to the right side. Drain the heatsink itself.
Very fast, a simple built up MOSFET.
The construction can be easily mounted on the original heatsink of the drilling machine.
Warning this method is not suitable for a commercial repair, it is on your own responsibility. Do this method only for unimportant machines and things which are under your permanent control. In this case I had the choice between throwing away the drilling machine as scrap or trying to repair, machine is old, (datecode old MOSFET propably 1986).

I coud not find the same MOSFET as original replacement - ok - some shops sell for 15 Euro plus shipping - but I have unsed smt MOSFETs and had nothing to do on that day.

Most modern power MOSFETs are available in surface mount technology packages, tht packages becoming seldom. The new MOSFET has a larger power capability than the old one and the same voltage. Soldering requires a hot-air-gun, a simple task. With a sodlering iron it is difficult or impossible, depending on power and tip-size. After removing fully the die, clean everything and put some solder-tin and flux, first without the MOSFET, than place the smt MOSFET exactly and solder with the hot-air-gun. If too much air, fix the smt during soldering via kapton-film or any other method.

application notes