SMD footprints

There are IPC guidelines that are generally pretty good. One for reflow that has minimal expansion beyond the pins, but enough and another I think is for wave soldering (yes, you can wave solder surface mount) with larger extensions. The 10 mil might be good at the toe where most provide a significant extension. The sides often are only a couple of mils if that and the heel can be as little as 5 mil, but don't hold me to any of these numbers. It's been a while since I laid out a footprint.

What is the "Linux pcb" tool? I didn't know anything came with the Linux distribution and there are a number that are available for Linux and are even primarily built for Linux with Windows support being an afterthought. KiCAD is a popular one.

Standard footprints work well with stencil and commercial builds. Extended pads work much easier for hand soldering and prototyping. But it takes up more space.

apt get install pcb (and gerbv)

pcb allows auto generation of footprints and traces. I have hundreds of traces auto-gen using it.

I use "sed s/350.08mil/360mil" to extend the footprint and verify it with "grep 350.08mil | wc == 100". 350.08mil is the outer position of the tqfp100 pads. Fortunately, there are exactly 100 occurrences of 350.08mil.

It's a tool called "PCB" that runs on linux. part of the gEDA/gaF suite. I think the same D. J. Delorie who posts here occasionally is/was somehow involved in its development.

With CERN's recent investment in KiCAD, and the resulting improvements, interest in gEDA and "PCB" has waned.

yeh, afaict it hasn't had any developement since 2013 or there abouts

It's good enough for me. I don't really use much of the UI, just for preview after auto-gen. Mostly using it for generating gerber files.

On the topic of wave solder, you need to glue the parts first, that's the normal way I guess

Is it possible to use solder paste, pick and place, flip the board and wave solder?

Through-hole. A lot less bother.

I suppose in theory yes - if reflow tech uses high melting alloy and the wave solder alloy is a lower melting point alloy and temperature control sufficiently good. Never seen it done.

Personally I have used mixed through hole and glue dot SMD wave solder technology with great success. Also two sided reflow with the lightweight parts held by surface tension and bigger ICs all on the topside.

piglet

Not sure what you are describing. If you mean using glue, yes. One outfit wanted to do that with my board. I never found out why, but someone finally said it was not necessary.

Yes, but i would need to do a lot of custom work. The pins are 20 mils apart horizontally. I need to bend them down and rotate 90 degree and laser drill less than 4 mils wide, perhaps oval holes.

No, the part does not come in 100 pins DIP.

Well that's a shame. The demise of Western civilisation can be traced back to the introduction of SMT.

Nah, it was this Austrian couple that got shot in their car. :(

Cheers

Phil Hobbs

We do double sides SMT every day without using glue. I thought you had to use glue, too 20+ years ago.

But we stuff the through hole parts on those double sided SMT boards.

of course, no problem doing SMT on one side, through the oven and then stuff and wave solder the through hole parts.

Double sided SMT reflow is one thing, but trying to run SMT through a wave solder bath without glue seems a bit risky. If you are describing single sided mixed reflow and then wave soldering the other side, that should work.

You might want to take a look at the currently-available footprint libraries for the KiCAD tool. Many of the SMT footprints come in both standard, and "hand-solder" varieties, with the latter having extended pads.

I did something similar when I made some SMT-to-through-hole adapter boards for the SMT versions of the Murata 10.7 MHz IF filters. I ended up adding a couple of millimeters to the pads.

Changing footprint is easy enough, but i would need to relocate components for any more than 10 mils (1/4mm). Just wondering how much more i need for next batch of boards.

For now, i am bending the pins inward to expose some pad area. It's lot of work and not very accuracy.

No, we don't wave solder with SMT on the same side as the solder. That DOES sound risky but I guess that can be done somehow ?

However, we DO also have something called a "Selective solder machine" which automatically (programmed) solders individiual through-hole leads, usually larger bus-bars on the bottom which could have SMT parts on it. It isn't really any faster than soldering by hand but is a lot more repeatable.

boB

Somehow? Yes, glue the parts on the board.

Yeah, that's why I let assembly houses handle my boards.

Yes, for production, but i need to do it by hand myself for prototype.

I am going to push some pins out for prototype, in order to expand the pads by 50 mils.