# Vintage HP Boards - Is it just a flash?



## snoman701 (Jan 25, 2017)

Just curious, as I have access to more, but don't want to buy them if it's just a flash.

I think they are out of vintage digital scopes? Not entirely sure.

I have read that they are good....fwiw, I tried the pencil eraser. I didn't make it through...maybe I have the wrong type of eraser?


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## g_axelsson (Jan 25, 2017)

Hard to say with full certainty, but older HP boards usually are fully plated, even under the solder mask. The boards I've found like that only had solder mask on the bottom side.

A good way to test the plating is to peel a trace from a circuit board, using a knife. Then put it in a test tube with nitric acid. The copper will be dissolved within minutes and you can watch how thick the traces are. If it is flash it often breaks down into tiny flakes.

Göran


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## snoman701 (Jan 25, 2017)

Yeah, these are old. Quite a few sidebraze chips. Haven't found any really good chips yet, but a few in the $20 range. 

I'm up to over a lb of 40 pin sidebraze though...and that's cool!

Thanks


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## Findm-Keepm (Jan 28, 2017)

I've got 30 or so HP backplanes for an old analyzer. Gold plated, but BURIED under Parylene! Removal method involves HF acid, not for me. So I'll hold them until I either sell to someone or somehow find a safe way to remove the Parylene. And yes, I've tried NaOH methods, no joy.

HP used Parylene extensively - in 2M board repair, we were taught abrasion removal for replacing soldered components, but for a whole board, it's impractical...

http://www.paryleneconformalcoating.com/parylene-coating-removal


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## philddreamer (Jan 29, 2017)

Another way to "remove" the Parylene is, to leave the boards out in the weather... :mrgreen: 
After reading the post, I remembered I had some outside... for about 2 years!

Take care!
Phil


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## snoman701 (Jan 29, 2017)

I'll try hitting them with the sand blaster just enough to scratch through the parylene. If the NaOH can get to anything, it'll be toast.


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## geedigity (Jan 29, 2017)

What if you froze the boards and then gave them a couple whacks with a hammer. If regular freezing doesn't work, you could try liquid nitrogen. I just wouldn't freeze the board solid though. I have never tried it but I have worked with liquid nitrogen. It seems that it would allow for the coating to easily shatter. Make sure you wear insulated gloves, apron, pant legs over boots (the other way can hurt if you spill it) and a face shield.


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## g_axelsson (Jan 29, 2017)

geedigity said:


> What if you froze the boards and then gave them a couple whacks with a hammer. If regular freezing doesn't work, you could try liquid nitrogen. I just wouldn't freeze the board solid though. I have never tried it but I have worked with liquid nitrogen. It seems that it would allow for the coating to easily shatter. Make sure you wear insulated gloves, apron, pant legs over boots (the other way can hurt if you spill it) and a face shield.


Parylene is really tough, according to https://www.nbtc.cornell.edu/sites/default/files/Parylene%20Information%20Sheets.pdf


> Steel panels coated with Parylene C and chilled in liquid nitrogen at -160° C withstood impacts of more than 100 in-lb in a modified Gardner falling ball impact test. This compares with values of about 250 in-lb at room temperature.


I had a couple of depopulated boards in copper chloride so long that it totally dissolved the copper conductors under the solder mask, I think it was a few years between putting them in copper chloride and I finally decided to do something about it. To get the gold I scrubbed the cards with a steel brush and then dissolved the gold from the solder mask and gold mixture.

The only rational way I can see to recover the gold in a decent time frame with minimal labor is to use a furnace and smelt the boards.

Göran


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## snoman701 (Jan 30, 2017)

Anybody tried tetrahydrofuran per US patent US4734300 to Hughes?

Supposed to penetrate the parylene, and is otherwise a pretty mild solvent.

My biggest concern being the everpresent danger of organic compounds / strong acids.


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## Findm-Keepm (Feb 8, 2017)

snoman701 said:


> Anybody tried tetrahydrofuran per US patent US4734300 to Hughes?
> 
> Supposed to penetrate the parylene, and is otherwise a pretty mild solvent.
> 
> My biggest concern being the everpresent danger of organic compounds / strong acids.



At 15-25ml per board to remove the parylene, it's too expensive to use for recovery purposes. We used it at 2M stations in the military to remove areas of parylene around a large component. For simple resistors and other 2-3 legged parts, abrasion was approved, but for the 28-40 pin stuff, tetrahydrofuran was used - it dissolves slowly, so you have to flood it frequently.

I kinda like the weather idea - perhaps a bombardment of UV light at night, and sunlight during the day?


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