Reflow soldering (diy) question

I personally haven't done reflow but I've seen a lot of success stories. I'm not sure what you mean by "fill up the holes". If you don't put solder on the holes they can't fill up.

With reflow you simply put solder paste on the pads using a stencil(or not, there are some that use a special paste that seems to work well without a stencil) and put the components on it(possibly using some type of tack to keep them in place) then heat it up.

The hardest part is going to be getting the components properly aligned. Solder paste and pads tend to have a natural aligning effect due to the the paste's surface tension. If you put to much or not enough or your pads are not correct you may have problems.

Best thing I can tell you is to watch some of the youtube videos and get started. Do a test and see how it goes then maybe ask questions. It's kinda hard to "help" when your not really asking any questions. If you are going to do it any time there is no time like the present ;)

BTW, the other "hardest part" is the reflow temperature profile. Some guys have gotten away with using the "built in" profile and that "Special solder paste" I talked about. You tube has many more answers than you'll find here.

Also, there is no reason why you shouldn't be able to reflow the same board more than once. Once the components are "locked" in they shouldn't much much and an additional reflow will only stress the components and pcb thermally but shouldn't do much mechanically(unless you leave it in too long ;).

As far as holes filling up, I mean the normal amount of solder plating they use on the boards at the PCB house. Probably wouldn't fill up I guess.

I have a nice toaster oven so I'll give it a try on some practice boards.

I was fine till SSOP came along.

use on the boards at the PCB house. Probably wouldn't fill up I guess.

what the pcb house adds is just a coating, you need to add solder paste to the pads you want to solder

-Lasse

Yes, I have done many hundreds of boards this way. You don't get the tight overall temp equalization of a multi-zone oven, but it works out remarkably well.

I have a pick and place machine, and a process related to PCB etching that makes the solder stencils. (A brass stencil is a lot like a PC board with no fiberglass substrate.)

The trick I found was to actually measure the temperature of the board by poking a thermocouple into a through hole near the center of the board, or in one of the middle boards if running a batch of small boards at one time. I tried just hanging the thermocouple near the board and ended up frying a board badly! Apparently the board and the chips absorb way more IR than the little thermocouple wire.

And, you need a ramp-and-soak temperature controller. I lucked into a good one from Omega on eBay, and also got a lifetime supply of tiny thermocouple wire. The ramp-and-soak controllers run about $800 new, so you really want to get one on the surplus market if possible. The Chinese outfits are now making really cheap controllers, but I don't know if they have ramp and soak options, yet.

Oh, I do the boards in two passes. I apply solder paste and stuff the backs (which presumably have small parts only) reflow, then paste and stuff the front, and reflow again. Never had a problem with it. You have to support the board for the 2nd reflow so the back-side parts don't get disturbed when hot. Never had a problem with through-holes filling with solder, unless I got careless and dripped a glob of paste on the board.

One word of caution, the STENCIL is the KEY to SUCCESS! If you have too big apertures in the stencil, then the chips tend to float away on a lake of solder, and will not be accurately aligned with the pads. So, ALL apertures should be smaller than the pads. Experience will tell you how much to reduce the aperture area, it is not linear with pad area.

Jon

How thick is the stencil you used? 0.010 or thicker?

Cheers

on the boards at the PCB house. Probably wouldn't fill up I guess.

We reflow surfmount parts and add the thru-hole stuff afterwards. Works fine.

A convection oven might be better, if you have one.

Even 0805s are starting to look big to me.

John

converted toaster oven.

to do this --

components later? (including through hole?)

imagine you have to do the entire board at one time? no exceptions?

I do LLC and small BGA packages using a waffle iron. The waffle iron has flippable plates, waffle on one side, smooth on the other side. I use the smooth plates. I don't use solder paste. I tin each pad, coat with flux, place the part and stick it in the waffle iron. I tin a pad near the edge so I can see when the solder melts. I install the rest of the parts (smt & thru hole) by hand after the waffle iron session.

Oh, no. I started with .005" and now use .003" brass shim stock. I clean them to remove the anti-corrosion coating and then laminate them on both sides with dry film PCB resist and expose with a pair of mirror-image artwork made on litho film with my homemade laser photoplotter. Then etch in Ferric Chloride just like a PCB.

These work pretty well, but I am still learning the ART of figuring out what aperture to use for each type of component. If the apertures are a little too big I get solder bridging, which I can deal with. If a little bigger the chips float out of alignment and it is a big mess to remove and resolder them.

Jon

Interesting process. The lack of a cheap stencil has held me back. But the brass shim stock is a great idea. Good info here...

Cheers

A picture of a 'waffle iron' would be good.... not come across that term before.

Yeah! Well, I already had all this process worked out for PCBs, which I very rarely do anymore as the services are so cheap now. I built a laser photoplotter with 1000 x 1000 DPI resolution, so I can make accurate films on litho-type silver film. I got a Kepro dry film laminator on ebay years ago, and found a Kepro spray etcher in the dump, it had a tiny leak that I fixed with some epoxy.

I now make apertures as narrow as .011" and can probably go a little smaller. I am still working out the best aperture reduction for various lead pitches, but mostly have it worked out. I have used this to do solder paste for chips down to .65mm and even .5mm with pretty good results. My P&P machine has no vision, so placement accuracy is a bit low for these parts. I usually nudge them for better alignment after placement.

Jon