Microscopes and Solder Masks

RE: Microscopes and Solder Masks

Fred27 — Tue, 17 Jul 2018 07:58:12 GMT

Getting back to your original question, I think it's normal not to try putting soldermask between SMD pins of such a small pitch. That board looks fairly normal to me.

I can't remember where I read it, but I'm fairly sure the recommendation is not to try mask between the pins as it tends to flake off. Any misalignment may also mean you could get soldermask on the pads. (I'm thinking of 0.5mm or 0.4mm pitch LQFP and QFN packages here)

I'm now going to go search and see if I can find more info. If anyone else beats me to it feel free to correct me.

RE: Microscopes and Solder Masks

Fred27 — Mon, 16 Jul 2018 17:26:47 GMT

Nice microscope. I've got the same one. I got mine with a camera included but it captures a much smaller area than you can see through the eyepiece. I intended to sort out something better but haven't managed to yet. Tried a DSLR C mount adapter without success.

RE: Microscopes and Solder Masks

rachaelp — Mon, 16 Jul 2018 11:47:33 GMT

Hi Frank,

I'd been looking at various microscopes for quite a while, hoping to find a bargain used one from a high end manufacturer. In the end I did the same as you and went for one of the Chinese ones. I'm not sure which brand yours is, is it an Amscope? I went for one of those in the end as I had seen good reviews about them on various sites. If you follow Louis Rossmann on YouTube you'll probably have seen him explaining why he chose his.

With regards to the camera, I got one in the package I bought but to be honest I will probably replace it eventually. It's not particularly high quality camera and it's USB2 so the frame rate is a little slow so you see lagging between the screen and reality. I'll probably try and get a higher resolution HDMI camera. There are a lot around on eBay/Amazon which all seem to be of Chinese origin and have similar design. I've not seen any reviews of these or recommendations for ones which are considered to be good though. You probably did the right thing getting just the microscope without the camera because now you can just get whatever camera you really want to go with it when you are ready.

The first thing I did when I got my microscope set up was put some of my boards under it and see what they looked like close up. I've not seen the solder mask issues like you and Shabaz have reported but I can see how easy it would be for that to happen. I didn't have to hand any boards from the really cheap prototyping manufacturers though and I usually define all my solder mask apertures in my libraries for anything fine pitch. One thing I did notice on one of my boards though was that I could locate the position of buried vias within a PCB because I could see little bumps (and they are very little in reality) above/below them on the board. I'm not entirely sure the cause of the bumps, maybe air trapped in the buried vias expanding when the boards were reflowed? It's not something I was expecting to see and it makes me wonder if there may be any long term issues with the vias or any traces which run over those vias on other layers in the long term.

Anyway, nice new toy! I'm sure you'll put it to great use and it'll be interesting to hear how you get on with it.

Best Regards,

Rachael

RE: Microscopes and Solder Masks

genebren — Mon, 16 Jul 2018 02:04:03 GMT

Frank,

Nice microscope! I found a cheap, used Nikon that has been the best tool ever. It is so much easier to do a decent job soldering, when you can actual see what you are doing. I am sure that this is going to come in handy for you. I really like the c-mount option (wishing that mine had one) as it would be nice to use the microscope as normal and be able to take pictures of the work.

Gene

RE: Microscopes and Solder Masks

shabaz — Sun, 15 Jul 2018 23:53:46 GMT

Hi Frank,

That looks like a nice piece of equipment : )

2mil sound good, or maybe a tiny bit higher may be preferable if you also plan to use prototyping services in China.

If you look at the fourth photo here:

Low Cost PCBs - What Can They Look Like?

(the QFN part photo), the solder mask gap was 2.7mil. Since the mask was offset slightly from the copper (they don't get it entirely accurately registered), some of the solder mask ended up on the pads, but not a lot. So in summary anywhere between 2-3mil sounds like a reasonable guideline. And even if it gets slightly on the pad, it isn't such a big deal for most reasonable sized parts, so 2mil should be good.

If it is a TI part, they may offer information in the datasheet down to mask gap although that might not be always the case (its usually only needed for very unusual parts or very tiny parts).