Brads Electronic Projects Forum

Our company had our own thru-hole assembly equipment; but since going to SMT, we've always farmed the assembly out. I've seen the equipment working at the industry trade shows though. It's very impressive how fast and accurate the machines are. My next PCB layout for work will probably put parts on both sides. This will be the first time I've put more than just a few parts on the back.

I must admit, i've never seen how they actually get SMD components to stick on both sides of a PCB. It's easy enough to use a reflow oven with components on one side, but if you try and flip the board over and put components on the other side, the components then fall off the first side...

I believe they put a tiny spot of epoxy under the parts (especially the ones that are too heavy to be held on by the surface tension of the solderpaste or molten solder), and let it cure before putting the board in the oven. The epoxy goes between pads so it doesn't interfere with the electrical connections. In the case of BGAs or something where there's no place for a spot of epoxy, that side might have to only be on the top in the oven, or maybe tiny parts will be held in place by the surface tension of the solder the second time the board is in the oven.

That makes sense Garth, I wonder if they are able to extract some sort of 'glue' placement information from the gerber files, or if they have to make it up themselves at the factory?

I expect it is derived from the XYRS file, ie, the spreadsheet file you supply to the assembly house that tells the exact part to put in each place, along with X and Y coordinates and rotation (what angle to put it at), and which side of the board to put it on.