Somewhat of a peculiar board: repairing old portable cd player Technics SL-XP150

[pplaninsky]

Hi,

I am repairing an old cd player.
As usual, such old portable devices are damaged by forgoten leaked out batteries.
I am just posting here, because that particular board is somewhat of curiosity.
Initially, I thought it is single sided, but that could not be.

The bottom is standard green solder mask and copper traces.
However, the top side is really printed. If you look close on the pictures - you will see that all resistors are black (graphite) like prints.
The traces looks like some silver inc.

Initially I thought that this is just some kind of solder mask.

That device is circa 1993. Having listened multiple time to Dave and Chris bitching around printing boards with printer, that caught me by surprise.

a) Can you confirm that this is really printed-printed board?
b) Wasn't that audaciously expensive in 1993? I guess not - it looks like cost saving actually?
c) Do you know how they did it?

Thank you!

[shakalnokturn]

Hello,

Must be some variation of thick film technology:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjww8vQwbX4AhUzhc4BHYCtD50QFnoECAQQAw&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FThick-film_technology&usg=AOvVaw0VuCJbftZOL4_lalcjx4nG
Was not that common but could be found in the late '80s early '90s when a highish level of integration was needed. (Mainly portable devices, If memory serves Sony and Hitachi used it often.)

[pplaninsky]

Thank you!
Yep looks like it.

Still can't imagine why this would be a preferred way, instead of a normal copper PCB with SMD parts on it....

[pplaninsky]

Reading about Thick Film technology, it actually says it is done on ceramic substrates, because they need to fire it at 850 degrees. C And that PCB is definately not ceramic.

[pplaninsky]

OK. That makes sense:
As a low cost manufacturing method it is applicable to produce large volumes of discrete passive devices like resistors, thermistors, varistors and integrated passive devices.
Thick film technology is also one of the alternatives to be used in hybrid integrated circuits and competes and complements typically in electronics miniaturization (parts or elements/area or volume) with SMT based on PCB (printed circuit board)

[SeanB]

Done because you can make the board really cheap. Use single side SRBP board with copper only on the one side, and then etch the bottom to make all the traces there. Then you use a NC drill to make all the holes, going through 10 boards all stacked up at once. Follow that with a bed of nails tester, to probe every hole and check all the tracks are intact (optional, you can just have a person look at the board to see all are drilled). Then into a frame, and silkscreen on the bottom solder mask on the board, followed by an oven to cure it. Flip board over to the next jig, and silver loaded ink is applied to the top, going down the through holes to fill them, then drying and clearing the holes for component legs. Quick heat cure, and next screen puts carbon loaded ink on board, again with quick heat cure. Then screen print with a black soldermasks for the top, and after the final oven cure there is a final screen with UV cure varnish, to seal the silver inks and carbon from air for a few years, so they will stay stable.

Yes a lot of process steps, but cheaper in volume, especially as all the large holes and the final shape are made using a large press, punching the unwanted holes, and the board final shape, all at once with a large die set. single side SRBP board, literally sheets of paper and phenolic resin pressed and heated, with one copper sheet on the one side, in a large press with heated die. If you are making thousands of boards, in batches over a period of a few years, and you can easily change board type simply by omitting steps in the screen print process, and have amortised the machines over decades, you will carry on with this. Any board that is not critical can have this process done, and it saves money and time in assembly, no need to put wire jumpers, resistors, but still have 99.99% finished assembly rate success.

[pplaninsky]

Thanks for the detailed explanation.
Unfortunately, I think the silver traces have degraded on the top side.
Not sure if it is because the battery leak or just because of time.
Many connections are broken. This board is beyond economical repair.