solder pasting thru-hole parts

For the DIN connectors? I'd have them wave-soldered. Yes, it's still done. But make sure it is not this unleaded stuff if you are exempt for export. I had the "pleasure" of soldering a lead-free VME extender because lots of solder joints were flakey. 576 solder joints with the Weller cranked to the hilt. Oh what fun.

I think they would still want a stencil to apply the paste. But if they need to manually insert components anyway. Solder by wire is not much more difficult anyway.

We have DB (die-bond), SMT and TH on a small board. By the way, do you guys DB first or SMT first? Our guy wants to SMT first because of the bump in DBed board. We would very much want to test out the DB before SMT.

Yes, also for SMT! If you have a combination of through hole and SMT (not BGA) then it is very economic to put the SMT parts on the solder side. This way the through hole parts and SMT parts can be soldered in one go.

These things aren't press-fit?

Is there a business case for creating solder loads that pop on the leads of TH parts after they're on the board? They would be pick and place parts on tape and reel. (I don't know how the P&P machines would like to place little toroids on top of leads. I don't know how the parts would stay in place during the process. But I see glue.) Then you can pop the board into a reflow oven. I think this method could get more solder on the leads than a blob of paste that runs.

Reflow the SMD and eat the labor to hand solder the thru-hole components. Far cheaper in the long run for short-run (low count) programs, even if it is a large number of parts per assembly.. Also some thru-hole parts may not like the thermal profile of a reflow oven.

So unless you are already contract Mfg I wouldn't. If you are doing SMD reflow in-house, I would hand solder the thru-hole.

Not all parts can handle the thermal profile of a wave solder process. Only certain components can be placed on the solder side in a mixed technology PCB assembly.

The concept would seem to be viable, but..what prevents the parts from falling out? How about taking a modified page out of the bubblejet design; leave the board + parts upright and with a pulse of air (nitrogen so as to not contaminate solder paste) shoot a blob of solderpaste? Index PCB position as needed. OR.. Be crazy like me, and screen the paste on BEFORE loading parts..

Must have been that !wonderful! SAC alloy that everybody and their pet goldfish use... Sn96.5Ag3.5 has a much lower MP and is a breeze to use with normal soldering systems..and the surfaces look very shiny!

I think tey are called preforms.

top class contract houses can do selective wave soldering. There is a fine solder jet squirted at the board, which moves on an X Y table. Very clever.....

Some of the parts, like DIN connectors, have retaining tangs. Others, like relays, could have a few pins clenched, or be glued, or we could make a retainer plate to hold them in while the board is inverted.

One can buy n/c paste/glue dispensing machines. I wouldn't like trying to invent a solder paste shooter thing. It might be handy to have an n/c glue dispenser around, too.

Screen-pasting thru-hole pads and then inserting the parts is messy, and it may be hard to screen enough solder to adequately fill the hole. I'm talking 35 mil or so holes, with some blade-type pins, so I'd need a lot of solder.

I guess we'll have to experiment.

John

We have a selective solder machine, that looks more or less like a drinking fountain on an XYZ table. We mostly use it for connectors and transformers.

Personally I do not spec in press-fit. We had problems in the past. Then one day, sales reps were in, touting that press-fit was the cat's meouw. Sez 99.9-something percent contact reliability. We had a bazillion contacts per system. My hand goes up. "Yes, please." ... "Sir, could you tell us which one of roughly 3000 contacts would go open?" ... silence, mumbling, more mumbling. The meeting ended shortly afterwards.

No idea. It did not have a low melting point and I just took regular leaded solder and re-soldered it all. No more problems from then on.

I would love to see such a "wave jet" machine in action. I have seen a lot of solder processes. That would be interesting.

Could make for some particularly interesting accidents if you forget your PPE. Brings a whole new level of weird to "Touch The Stove", eh?

Tim

Not yet solidified crystalline lattices.

I don't think the book would sell... :-)