Name that part! (electronics)
December 21, 2010 2:33 AM   Subscribe

Name this electronic component / construction technique! Found inside a late 1980s Datron 1081 bench multimeter.

Closeup 1: four big resistors at top center.
Closeup 2: same four big resistors at left 1/3.
View of the entire board.

Note the unusual solder terminations on the four big resistors. Several of the large film caps use them too. They look like little white pads inserted into the pcb.

What do these mounting pads do and why were they used in this design?
posted by ryanrs to Technology (11 answers total) 1 user marked this as a favorite
Response by poster: Just to get the blind speculation out of the way, I can guess they're for creepage or leakage. What I'm looking for are specific details and especially application documentation from the manufacturer.
posted by ryanrs at 2:34 AM on December 21, 2010

Don't know if it has a name, but they're basically a version of through-hole eyelets. The purpose is to provide a mechanically & thermally stronger joint for heavy or hot components.

Normally they're copper eyelets either interference fitted or crimped into the hole, and then soldered. I've also seen ones that are fitted with a ceramic collet, but those look like plastic?

Google "pc board eyelets" and you'll find plenty of manufacturer / application info.
posted by Pinback at 3:54 AM on December 21, 2010

Best answer: Huh, I was sure that I'd seen them in the NASA Pictorial Workmanship Guide, but they're not there anymore, or never were. I was looking under "swaged terminals" though they also look like ceramic solder pots.
posted by fake at 3:56 AM on December 21, 2010 [2 favorites]

Response by poster: Ok, heat makes some sense. The resistor values are 22k + 22k + 27k + 27k = 98k. The Datron 1081 had a max input of 1000VDC. V2/R = 10W, which is probably right around max Pd for those resistors.

But they're also used on the capacitors, which presumably don't get warm. (You generally don't roast your 0.1% tolerance, hand-numbered precision film caps.)

Another few details I just noticed:
1) The low-potential end of the cap string does not use an insulated eyelet.
2) The white wires coming from the side panel (not the relay) mostly use non-insulated pcb terminals, except for the one connecting to the R and C strings.
3) What the hell is going on with the solder mask? Is that intentional?
posted by ryanrs at 5:36 AM on December 21, 2010

Response by poster: That NASA Workmanship Guide is great. Thanks, fake.
posted by ryanrs at 5:45 AM on December 21, 2010

Actually they do look like these swaged terminals here in the NASA Guide at section 6.05.
posted by exogenous at 6:08 AM on December 21, 2010

That's a busy board. Meaning there's LOTS of stuff on it. I've seen this type of soldering and while the small caps ( we always called them vias) were neutral electrically, they did essentially add more work space for the person soldering. The parts MAY also have been added at a later stage in the process for whatever reason. Early surface mount combined with hand soldering? That would explain the solder mask, I think.
posted by pentagoet at 7:29 AM on December 21, 2010

I've also seen this done in a scintillator, on only the high-voltage contact points of a board (up to 2kv), and I think it was to create a spark barrier - the plastic can't ionize, so an arc would have to take a longer path.

My assumption is that the resistors and cap in question are part of the high voltage section of the multimeter.
posted by -harlequin- at 11:44 AM on December 21, 2010

Response by poster: Harlequin, yes, I believe those components connect to the DMM's 1000V input terminal.

Exogenous, which swaged terminal? I don't see anything like it on that page. It's certainly not a turret terminal.
posted by ryanrs at 11:55 AM on December 21, 2010

What's on the other side of the board where the large solder terminations are? Is it possible that there are terminals or connectors on the other side of these things?
posted by buzzv at 7:02 PM on December 21, 2010

Response by poster: Dunno.
posted by ryanrs at 2:53 AM on December 22, 2010

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