Practical PCB Production Soldering?

Are the PCBs heat-sunk to the plate?

Solder reflow, especially lead-free, requires fairly precise time-temperature profiles, which is usually done in a multizone conveyer reflow oven. Preferably in nitrogen.

Why not (have someone else) reflow the boards, then assemble to the power plate?

Incidentally, it sounds like your assembly might be hard to maintain, especially if the boards are stuck to the plate with silicone grease or adhesive. I'd suggest something less messy, like the Bergquist sil-pad things and PEMs with screws.

Packaging is 50% of electronics.

If the parts are large or glued down you could try hot air. Another good diy technique is infra-red. Heat transfer up through the metal plate and through the pcb substrate sounds trickier to me but willing to be corrected.

What size is the assembly and what kind of parts (largest and smallest) are involved? Is this a one-off or will it be recurring?

piglet

I do reflow of standard SAC305 solder with a GE toaster oven and a thermocouple ramp and soak temperature controller. I have to poke the thermocouple into a through hole in the board to detect actual temperature, the air doesn't get heated as hot as the boards, due to the IR. This oven holds an 8.5 x 11" piece of paper (just barely). I normally ramp to 180 C, hold for 1 minute, then ramp to 235 - 240 C hold for 1 minute, and then ramp down. 400 C will smoke most electronics.

Jon

It is a narrow pcb 2 feet long by 1 inch wide... Should be recurring, but in prototype stage... thanks jb

thanks. pcb not heat sunk down. I'm prototyping, and doing hand wiring, so thinking about pcb. Easy to get a 2 ft. pcb x 1 inch?

jb

OK - Hw do you apply solder? I started my career (heh heh) in metallurgy, so have built a few furnaces.

That should fit on a standard panel, so should be OK.

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that's a big panel, where we normally get PCBs maximum size for two layers are 585 x 435 mm (~23"x~17")

-Lasse

John Know any sources of single sided board, 23" or so? tia JB

look like these will do 500x1100mm

-Lasse

Solder paste is applied first with a stencil and metal squeegee. I use a .003" stencil made from brass shim stock, I coat it with dry film resist, expose to master artwork on both sides, develop and then etch just like it was a PC board. You can have stencils made fairly cheaply, but since I already had the gear to do it, I do it myself.

After the paste is applied, I place the components with a pick and place machine, then put it in the oven to reflow the solder. Works very well.

Jon