Thin boards in oven, what panel size? - Page 1
Forum section: electronics / general

author: loki42
author_rank: Frequent Contributor
timestamp: July 26, 2022, 11:38:53 am
content: Is there are reason for going for larger (or smaller) boards when designing array/panels for use with a chain conveyor oven?My panels range from 0.6mm 2 layer (for touch with hatched ground) to 1.6mm 4 layer. They are all around 100mm X 100mm. I'm planning to go for smaller panels for the 0.6mm to reduce the chance of sagging but I'm not sure what max sizes are okay.The oven is an Essemtec RO300fc-c so my max width is limited to 300mm. The 0.6 mm board only has a few components on it as most is a touch sensor. I'm planning to use routing for the panels with mouse bites not v scoring but open to either if it's a good idea. All the components on the touch board are in one corner, 25mm from the nearest edge and there's only a few parts. I'm contemplating running them bare if it'll cause less issues. I've got a vacuum destacker so they aren't hard to feed.

author: SMTech
author_rank: Frequent Contributor
timestamp: July 26, 2022, 01:00:47 pm
content: 100mm sounds fine to me. Yes you'll see more sag than on 1.6mm but its not going to fall off the chain pins or anything. I've put some double sided 0.6mm panels thru fairly recently of approx that size, quite densely populated with a solid border 10mm all round and pipped/routed circuits. I've also done some Rogers material singles of that size with an almost complete copper coverage on one side, they sucked because they curl up as soon as you glance at them. Makes handling and printing annoying, still fine for reflow.

author: loki42
author_rank: Frequent Contributor
timestamp: July 27, 2022, 12:34:08 pm
content: would a 200 square or 300 x 200, 3x2 panel be okay for the 1.6mm boards? How about 100 x 200 long board for the 0.6mm? Apart from the touch boards the other boards have a decent amount of parts on each (around 100) so I'm not sure if a larger panel will speed up production by much or at what size it becomes problematic.

author: SMTech
author_rank: Frequent Contributor
timestamp: July 28, 2022, 07:37:59 am
content: Both of those should be pretty effective, however, as was suggested on SMTnet it doesn't hurt to test it out. If you see sag you don't like you can experiment with carriers or simple support structures. I have a v-scored 280*110mm 2up panel here (odd choice of alignment edge but there go) I did try it just for fun the wide way round and that of course dipped quote bit on the score, but it didn't break. When I visited other sites to see new Ovens, one place insisted on making panels to their std size, to keep their profile super reliably consistent. That was a pretty large panel somewhere around A3 size, however that Oven was the one I chose and as standard comes with both mesh and pins so we have that fallback option should we need to. So far however I only use the mesh for awkwardly shaped low volume boards or when the pin chain is busy with a different size. I would say perhaps that more than 2 boards across when using v-score probably not ideal but otherwise I think your panels are basically tiny.

author: Fire Doger
author_rank: Regular Contributor
timestamp: July 30, 2022, 07:32:08 pm
content: I am not familiar with Essemtec RO300fc-c but other types of chain oven have also a configurable chain in the middle. This eliminates sagging.The issue with thin pcbs are that (depending on manufacturer) they may warp. This may cause issues if it is double sided. You can try to stationary bake a thin empty pcb at 100° - 120° for a couple of hours and see how warped is after.Also having mouse bites increase the warp effect because there is less structural integrity, more flexy = bad.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 30, 2022, 07:47:51 pm
content: For thinner boards in particular, it can beneficial to try to balance the amount of copper on each side - I had some 0.2mm boards curl up like tacos.