circuit board masking - needed?

[kstagger]

Silly question from a guy who normally does P2P wiring or uses PCBs made by someone else.

I'm thinking of getting a circuit board made from PCB Express - one of the options is the prototype service that does not have a solder mask. Is this required for longterm use? ie - do the tracks get corroded?

[jcx]

the main problem is solder thieving without solder mask if you try smt with solder paste/stencil reflow

with hand soldering there is little problem

all pcb trace platings lose solderablity as they age/oxidize - at microwave frequency there can be additional signal loss due to the lower surface conductivity - for audio no measurable effect

[kstagger]

perfect- thanks!

[jitter]

Originally Posted by kstagger

Silly question from a guy who normally does P2P wiring or uses PCBs made by someone else.

I'm thinking of getting a circuit board made from PCB Express - one of the options is the prototype service that does not have a solder mask. Is this required for longterm use? ie - do the tracks get corroded?

This is the same problem you get as when making pcbs at home. After etching the pcb and wiping it with acetone to remove the photosensitive layer, I always sprayed them with Flux SK10. This is some sort of varnish that protects the tracks from oxidation and aids soldering.

[maxseeley]

For long term use you want to coat the board with a conformal coating. There are numerous options:

Circuit Specialists Inc. - 12 oz. aerosol, Clear Acrylic Lacquer Conformal Coating [UPS Ground Only] (419B-340G)

They seem to have cheap prices. Also, digikey, mouser, ....

The flux sk10 is a product that provides short term protection against corrison but not long term. The nice thing about the flux sk10 is you can still solder parts that are coated with it. The acrylic conformal coating must be removed to solder. In other words, you would wait till you are done soldering to use it.

[Juergen Knoop]

I use Plastik 70. While it is an acrylic lacquer, it is solderable, afaik longterm stable, and it isn't sticky like the awful SK10.
regards

[SirNickity]

I remember seeing a website that had a promising DIY home PCB kit. They actually cover the whole gamut from printing your layout, to a custom lamination machine (heat + pressure) to fuse the layout to the PCB.

The relevant part here is their technique for solder masking. If I remember right, you re-print pads-only artwork and transfer that to the etched board. Then you mask it, and go another round with the acetone to take the toner off again, leaving bare copper pads.

Their kits looked nice, except the boards were a bit thinner to fit through the laminator, and they used lighter copper.. I think it was 1/2 ounce..?

I bookmarked the site, but I've rebuilt since then so I'll have to check my archives disk...

EDIT 2: I also vaguely remember hearing about someone using something like petroleum jelly to coat the pads (with a Q-tip) so the mask wouldn't adhere when sprayed. Bake, then clean the board.. tada!

[jitter]

Originally Posted by maxseeley

zip

The flux sk10 is a product that provides short term protection against corrison but not long term. The nice thing about the flux sk10 is you can still solder parts that are coated with it.

I just had a look at a pcb I made about ten years ago and treated with Flux SK10 only: shiny copper and no trace of corrosion yet. I'll check again after another ten years have passed .