I came across an interesting video about soldering TO-3p transistors to a copper heat spreader.
https://hoppesbrain.com/2024/02/09/new-product-teaser-mt-200-to-to-3p-output-transistor-adapters/
While not an entirely new concept, I have been unsuccessful in the past with home-made copper plates and a soldering gun. I may have to try again now that I have a hot air rework station.
https://hoppesbrain.com/2024/02/09/new-product-teaser-mt-200-to-to-3p-output-transistor-adapters/
While not an entirely new concept, I have been unsuccessful in the past with home-made copper plates and a soldering gun. I may have to try again now that I have a hot air rework station.
Soldering semiconductors to anything is destructive and needless!
Most semiconductors can stand 250°C for less than 25seconds before damage occurs. Cooling them down rapidly to be withing the 25second period damaged the substrate and will reduce the tollerances of the semiconductor.
Adding a plate between the semiconductor and the heat sink will reduce the heat transfer capability as it will have introduced non flat surfaces and possibly foreign bodies within the 'joint'.
The correct method is to drill an M3 tapping size hole through the heatsink where required to fix the replacement TO3P transistor. Carefully tap the hole and countersink the hole to avoid metal contamination to the heatsink compound.
Fit the silicon insulator pads and install the semiconductor. If using Mica, use non silicon heatsink compound.
Job done and no damage to the semiconductor.
Most semiconductors can stand 250°C for less than 25seconds before damage occurs. Cooling them down rapidly to be withing the 25second period damaged the substrate and will reduce the tollerances of the semiconductor.
Adding a plate between the semiconductor and the heat sink will reduce the heat transfer capability as it will have introduced non flat surfaces and possibly foreign bodies within the 'joint'.
The correct method is to drill an M3 tapping size hole through the heatsink where required to fix the replacement TO3P transistor. Carefully tap the hole and countersink the hole to avoid metal contamination to the heatsink compound.
Fit the silicon insulator pads and install the semiconductor. If using Mica, use non silicon heatsink compound.
Job done and no damage to the semiconductor.
The whole point of the copper heat spreader is to avoid the thermal resistance of a silpad on the small transistor pad. The much larger area of the copper plate will then have a significantly lower thermal resistance with its silpad. Solder is a much much better heat conductor than silpad and conforms to non-smooth surfaces.
Reflow soldering of transistors with a heat pad is routine and has no risk if done properly (suitable heating profile). Look at DPAK and DPAK2 transistors for instance.
Reflow soldering of transistors with a heat pad is routine and has no risk if done properly (suitable heating profile). Look at DPAK and DPAK2 transistors for instance.
I understand your points. If a suitable replacement for transistors such as 2SC3264/2SA1295 or 2SC2922/2SA1216 existed in a TO-3p or TO-264 type package, I would be in complete agreement.
The closest replacement I know of would be MJL4281A/MJL4302A. Which at a quick glance looks ideal. Unfortunately there are some downsides to this part. This transistor has more than twice the Cob of the originals, making them harder for the driver transistors to drive. Looking at the SOA graphs show that the 230W rating is too optimistic. They still don't reach the power handling of the old 200W rated parts.
The same silicon die used in the now obsolete 2SC3264/2SA1295 is still being used in 2SC3263/2SA1294. This means the only difference between these parts is the larger package. If one can sucessefuly solder these currenty avalable transistors to a larger copper heat spreader, this is amazing news. Repairs that have otherwise been unfesable without a stash of old parts are now possible again. Some testing in an article update shows this idea may actually work: https://hoppesbrain.com/2024/02/23/validating-the-performance-of-my-mt-200-transistor-adapters/