-----Original Message----- From: cctech [mailto:cctech-bounces at classiccmp.org] On Behalf Of emanuel stiebler via cctech Sent: Thursday, August 15, 2019 4:23 AM To: systems_glitch; General Discussion: On-Topic and Off-Topic Posts Subject: Re: GW-DEC-1: A New DEC Prototyping Board On 2019-08-15 02:13, systems_glitch via cctalk wrote: DEC http://www.vcfed.org/forum/showthread.php?71177-GW-DEC-1-A-New-Quad-Height-… Was always hoping somebody would do something like that, but with the bus interface already on it ... ----- But which bus? There are three ... -----

Hi Jonathan, If you are looking for someone to make the boards, I know someone in CA. I'll try to dig up his contact info this weekend. Paul On Wed, Aug 14, 2019 at 7:14 PM systems_glitch via cctalk < cctalk at classiccmp.org> wrote:

On 08/16/2019 08:59 AM, systems_glitch via cctalk wrote: I'd There are few board houses in the US anymore, and they are usually doing aerospace or government work, and are quite expensive. Most of the supposedly US-based outfits now do almost all their fabrication in China. I use E-teknet, based in AZ, but their fabs are in China. They do VERY good work. In the distant past I did a lot of boards with US makers, but had a constant problem that they would charge me for electrical test, and then just cheat and NOT actually test the boards, just do a visual inspection. So, I ended up with 4-layer boards with shorts on the inner layers! And, only found those after stuffing the boards. A MAJOR pain, and I would blacklist those companies. Well, E-teknet has never done that to me. (The flying probe tester leaves TINY dots on the pads, so you can tell whether a board has been tested or not.) Jon

I've gotten the distinct impression that US board houses really are only interested in government/military/aerospace work. I've often wondered what it would take to set up a modern "no human interaction" line and if one could be even a little competitive with the Chinese on it.

Dwight, I spot check boards. I lack sufficiently sensitive instruments to measure actual thickness (even on a surface plate, it's the same for ENIG as hard gold with an 0.0001" indicator) but ENIG won't stand up to a few swipes with an ink eraser, whereas hard gold will stand up to it no problem. The main issue I've seen, in buying other people's products and projects, is board houses passing off ENIG as hard gold (and charging for it!) or claiming they're using "extra heavy ENIG" -- which of course isn't a thing, because ENIG is an ion swap! Thanks, Jonathan

On Aug 16, 2019, at 2:43 PM, systems_glitch via cctalk <cctalk at classiccmp.org> wrote: I'm sure DEC wouldn't have bothered with hard gold plating if their connectors were metallurgically incompatible :P The few busted DEC connectors I've replaced did indeed have selective gold plating on the contact surfaces. Most quality edge connector slots are similarly constructed.

From what I remember, the detailed analysis involves an "electrochemical series", which has metals like sodium at one end, copper closer to the middle, and gold at or near the other end. Metals are compatible if their potential value differs by less than a limit. The limit depends on the environment; in an office you can have a larger limit than on a ship where you have salt spray, or a tire factory with lots of SO2 in the air.

On Fri, Aug 16, 2019 at 2:27 PM ben via cctalk <cctalk at classiccmp.org> wrote: > On 8/16/2019 12:13 PM, systems_glitch via cctalk wrote: >> Dwight, >> >> I spot check boards. I lack sufficiently sensitive instruments to measure >> actual thickness (even on a surface plate, it's the same for ENIG as hard >> gold with an 0.0001" indicator) but ENIG won't stand up to a few swipes >> with an ink eraser, whereas hard gold will stand up to it no problem. The >> main issue I've seen, in buying other people's products and projects, is >> board houses passing off ENIG as hard gold (and charging for it!) or >> claiming they're using "extra heavy ENIG" -- which of course isn't a > thing, >> because ENIG is an ion swap! >> >> Thanks, >> Jonathan > > Is gold plating the best thing? I thought that gold plating only works > best when matching other gold connections. > Ben. > >

On Fri, Aug 16, 2019 at 2:53 PM Paul Koning <paulkoning at comcast.net> wrote: > >> On Aug 16, 2019, at 2:43 PM, systems_glitch via cctalk < >> >> I'm sure DEC wouldn't have bothered with hard gold plating if their >> connectors were metallurgically incompatible :P The few busted DEC >> connectors I've replaced did indeed have selective gold plating on the >> contact surfaces. Most quality edge connector slots are similarly >> constructed. > > It's been a while and I never looked in depth, but it most definitely is > not true that gold is only compatible with gold. > > From what I remember, the detailed analysis involves an "electrochemical > series", which has metals like sodium at one end, copper closer to the > middle, and gold at or near the other end. Metals are compatible if their > potential value differs by less than a limit. The limit depends on the > environment; in an office you can have a larger limit than on a ship where > you have salt spray, or a tire factory with lots of SO2 in the air. > > There are also some twists; I think stainless steel is compatible with > many things thanks to the alloy ("stainless") properties. In fact, I think > the subject came up in connection with failure analysis of coin cell > battery holders. The battery cases are stainless steel; the question is > what contacts are acceptable. Gold is; there may be others but some things > that are used in the market are not good choices.

You can look it up in an electronegativity chart for a quick "will these ruin each other" check. I think a lot of this comes from the SIMM era in PCs, where folks were told to only use gold-flash SIMMs in gold sockets, and only tin plated SIMMs in tin plated sockets.

On 2019-Aug-16, at 11:56 AM, systems_glitch via cctalk wrote: I've seen pieces of HP high-end lab equipment from thru the 60s that used tin plating on the PCB edge fingers, mating into gold-plated edge connectors on the backplane. Never quiet understood it, they (HP) were doing gold-plated edge fingers on other equipment at the same time.