Was this a thing? Looping diodes on vintage card assembly

[SpanishVikingNorCalEE]

You point out an importatnt detail I left out...

Early SMT mfg. lines tended to be extremely unreliable. My take on the whole thing was that if the line engineer for a given line understood what it really took to properly flow paste, and how smooth the pic-n-place line, as well as any conveyance between there and the re-flow oven running smoothly enough that it didn't bounce the heavier IC's out of their less than perfect adhesion to the land provided by the paste, then the solder would flow and whet properly to the lands and leads, and it would be reliable as the PCB itself generally. But wave solder and stuffed through-hole components were tolerant of a large number of PCB assembly sins that SMT isn't.


If the boards get fingerprints all over them going into the line, and the ovens aren't clean enough, or the line bounces components off their pads (even out of registration too far), or the oven's temp profile isn't right, then the solder quality suffers in ways that just didn't matter even on large scales for TH assembly lines (remember the 100% hand stuffed, often in some house-wife's kitchen a few hours each day, then going back to the assembly shop for wave-solder in their hatchback the next day. they generally worked, or at least the solder generally worked.).

Ah the good 'ol days. SMT was thought to be really hard in the beginning, but mostly that seemed to be the opinion of experienced TH assembly folks. Only some of them could see past their years of status-quo methods to understand that things like finger-prints, dust, hair, oil, smoke, or pretty much ANY other contaminate on the parts, the PCB, or in the oven's internal environment really mattered. They matter at any large scale weather or not anyone in QC noticed anything wrong or not.

That's  how the military got away with their  early ramp of reliable SMT assembly technology in the high reliability segment. They understood the science behind what they were doing, and had the discipline to follow that, and make sure their suppliers did as well.

I'm feeling a little nostalgic now for those 'good 'ol' days when assembly was easy, but computing was hard. :-)

[coppice]

Early SMT mfg. lines tended to be extremely unreliable. My take on the whole thing was that if the line engineer for a given line understood what it really took to properly flow paste, and how smooth the pic-n-place line, as well as any conveyance between there and the re-flow oven running smoothly enough that it didn't bounce the heavier IC's out of their less than perfect adhesion to the land provided by the paste, then the solder would flow and whet properly to the lands and leads, and it would be reliable as the PCB itself generally. But wave solder and stuffed through-hole components were tolerant of a large number of PCB assembly sins that SMT isn't.

Early SMT was all vapour phase. Reflow came later.

[Daixiwen]

I remember some electronic kits from the 80's where they said you needed to do that to all the diodes to prevent destroying them while soldering, so I agree with emece67.
I'm not sure if diodes were more fragile at that time or if they were overthinking it. I've never destroyed a diode with a soldering iron.

[rrinker]

 Heck, I've soldered some glass diodes with the leads cut off rather short (model railroaders are famously cheap buggers - so what if I can buy 1000 new ones for $1, I'll use the old ones I cutout of a previous layout!) and had no problems. I'd probably buy new ones in most cases, but the guy I was helping had a bin full of cut off ones removed from old layouts so we used them up. For soldering purposes, I'm not so sure - but for long term thermal change and vibration - I'd buy that. Though they had one of those diodes on the old Radio Shack kits - the first one I had had each component on a plastic block, with L shaped metal pieces you linked under the spring terminals to complete the circuits and plastic connectors to physically attach each block and that thing certainly got tossed around a bit and none of the semiconductors ever failed - and that kit would have been about the same vintage as an Altair micro. The later ones I had of course were in those wooden cases so individual components didn't get tossed about. I uncovered a part bag of the 50 pack of glass diodes Radio Shack used to sell that was carelessly tossed in a box full of random junk and while I haven't checked them all, I used a couple and they were fine. Stored, they were subject to fairly extreme temperatures (not sure of the actual manufacturer so no idea if outside the data sheet specs) plus they had stuff piled on top, and the whole box was rather tossed about since in general there was nothing fragile obviously in it. 

[mikeselectricstuff]

I've seen it occasionally. Reduces stress, both dynamic when inserting and static/thermal cycling etc. also provides useful test points

[David Hess]

The DO-41 package in glass is not very common anymore; most are now plastic.  I remember we used to get 1N4004s in the glass DO-41 package.

[duak]

In the mid-70's I built myself a digital clock that used a bunch of loose LEDs for the display.  Until then about the only semiconductors I fried while soldering were germanium signal diodes so I wasn't super worried about heat sinking the LED leads.  Sure as shootin', about half of the LEDs were dim or dead.  When I assembled the Altair front panel, with its forest of LEDs, I made damn sure to use a heat sink while soldering.

[David Hess]

I have had the same problem with LEDs and I suspect the problem is not the heat itself but the packaging and strain if the leads are bent during soldering.

[Nerull]

From the IPC-A-610 standard on lead forming: