I used to make double sided boards all the time using the syringe method. I did it manually but also used a low cost manual pick and place from Bomir that has a built in electronic programmable dispenser.

Unless the parts are big, there is no need for glue..especially on little resistors and caps. If you make a frame for the board (the Bomir had an integrated PCB holder) you can put pasted down and the parts, flip it over and place the other parts. Then of course you need a frame in the oven as well, but I never reflowed double sided boards twice.

Posted at 11:27 am on Oct 25th, 2009 by Mike M

My firm does a lot of our own prototype boards, and that team just reflows the boards twice. They do the side with the light components first, and then run that side on the bottom when they reflow the side with all the chips and inductors and heavy stuff.

Posted at 11:44 am on Oct 25th, 2009 by tyco

anybody know what function the board made has?

Posted at 12:51 pm on Oct 25th, 2009 by zhaiko

I could be wrong but that biggest connector looked like a phone jack. maybe its some kind of usb modem???

Posted at 1:13 pm on Oct 25th, 2009 by jamieriddles

couldnt you use a stencil for the solder paste and then do the epoxy by hand? seems like that would save alot of time.

Posted at 1:16 pm on Oct 25th, 2009 by Dave-0

@zhaiko : it’s an USB to I2C bridge.

Posted at 1:29 pm on Oct 25th, 2009 by vic

I used to do a LOT of SMT work (avionics, semi-custom actuator controllers) and we did all our repair and short run work by hand. No stencils, no reflow oven, no solder fountain. Magnifier lens, Weller soldering station, Kester solder spool and a steady hand was all we used. I didn’t even know about stencils until I was getting out of the industry. We would double-check our solder joints at X30 on the microscope to make sure the joints were flawless. It did take a couple days of training to get to where your joints were perfect… That didn’t come out right. :P

Posted at 2:03 pm on Oct 25th, 2009 by rallen

With that freaky music they should have had a Carl Sagan impersonator do a voice over saying “Billions and Billions of solder joints….”

Posted at 4:05 pm on Oct 25th, 2009 by vonskippy

This is a good refined method if you can’t afford manufacturing.

Posted at 5:56 pm on Oct 25th, 2009 by tj

On larger boards, wouldn’t the epoxy on the bottom make removal of defective or toasted components impossible? It’s tough enough to remove a SMT fuse on a heavily populated board without causing any collateral damage. I’d be afraid that the pads would be ripped up on this design.

Posted at 3:54 am on Oct 26th, 2009 by robomonkey

I would recommend using the epoxy for the underside as directed, but before reflow, applying paste to the top side and placing those components. Then reflow the board. The fewer thermal cycles, the better.

Posted at 6:26 am on Oct 26th, 2009 by Kylebostian

I work in the electronics industry. On double-sided boards, another stencil is used to apply a small blob of epoxy before the solder paste. The board is then run through the reflow oven, where the epoxy cures and the solder reflows.

The other side of the board can then be stenciled, populated and reflowed without the epoxy.

Posted at 8:55 am on Oct 26th, 2009 by jeff-o

Nice, but the most important piece of information hasen’t been discussed…which epoxy yields good results… If anyone has experience/suggestions
please comment….

Posted at 9:45 am on Oct 26th, 2009 by mike

There is glue specifically for this purpose. Loctite 348 is one such product.

Unless the part is really large, I don’t recommend the dual heat cycle. The glue should start curing before the solder reflows and hold the part on.

Posted at 9:58 am on Oct 26th, 2009 by Mike M

I used to work in the electronics manufacturing industry myself. The most common method is the one jeff-o mentioned, with the epoxy and solder paste being done with two stencils. Another method that also gets used is to stencil the epoxy, place the components, cure it in the oven, then stencil-place-flow the other side. Then the epoxied side gets soldered in a wave flow solder machine.

It’s ugly, and tends to result in a lot of minor rework to remove shorts, but it works and does get used.

Posted at 1:51 am on Oct 27th, 2009 by esker

What a surprise to see my little movie featured in Hack A Day, and a great pleasure too… Thanks!

The background: this movie was intended to explain our readers (/begin commercial/ Elektor is a monthly magazine for electronic designers and entousiasts, available worldwide in more that ten languages /end of commercial/) how-to-do low cost double sided soldering with a reflow oven.
The movie comes with an article, that was published in september and describe a bit more in detail the whole process/idea.

Using a pasta dispenser does not aimed at being faster but more versatile, we have here a lot of different project – what I like to call electro-diversity – but only produce a few protypes mostly used for test (destroying) purpose :).

So far I’ve tested two different epoxy glues:
- ref. SMA10SL from Electrolube
- ref. CB8006-V91 from Loctite
Everything went well in both cases; the Loctite is maybe a bit more fluid, is it a feature or a drawback, you have to decide. Both are 10 ml syringe, the Electrolube came with a plastic needle and a plunger, we got a Bundle Loctite so no idea if you can have it packaged with this two accessories too, anyway the plunger can be replace by a screwdriver, any kind of “Luer Lock” compatible needle will fit, be careful with medical one they stitch in.
I believe that with these two brands we have world coverage and you won’t have difficulties to find then anywhere.
But I guess any kind of “SMD Chip Bonder” (key word for your favorite search engine) will do the trick.

The board is indeed a USB to 1-Wire/I2C bridge.

P.-S. Don’t blame for the music please, did not choose for it ;-).

Posted at 3:42 am on Oct 27th, 2009 by Antoine