Solder masks

Community PCB Design
1

I’ve been thinking about getting into making PCB’s, and I’ve found good tutorials all over the web about how to etch the boards, how to lay out the components, and obviously how to do the soldering, but nowhere can I find out how to apply a solder mask! If I start making boards, I at least want to have a shot at making the boards look professional, and the solder mask sure would make the soldering easier (duh).

So:

What is the stuff, anyway?

Where do I buy it?

How would I apply it? Silkscreen?

What do you guys do at Sparkfun? I know you guys put solder masks on the boards you make. Someone wanna let me in on this secret? I’d greatly appreciate it.

2

I’ve never needed soldermask on my home-made PCBs, even with 0.5 mm spacing pads. It needs special equipment and techniques, anyway.

You should join the Yahoo Homebrew PCB group.

Leon

3

Greetings (No First Name Supplied),

bobtron3.2:
If I start making boards, I at least want to have a shot at making the boards look professional, and the solder mask sure would make the soldering easier (duh).

What is motivating you to make your own PCBs?

There is a worldwide surplus of PCB fab capacity

that is forcing down prices, and pressuring vendors

to offer better service (faster turns and tighter

specs).

bobtron3.2:
What is the stuff, anyway?

Solder mask (AKA solder resist) is a protective layer on

the outside of PCBs to assist in wave soldering. It also

provides environmental protection for the PCB metal,

and improves the readability of silk screen legends.

bobtron3.2:
Where do I buy it?

I don't know. I would imagine that there are chemical

supply houses that sell it in bulk.

bobtron3.2:
How would I apply it? Silkscreen?

Depends on your processing equipment and work flow.

Some resists are lacquer or epoxy based liquids that

are silk-screen printed. Other types are the liquid

photoimage solder mask (LPSM) inks and dry film

solder mask (DFSM). Both require exposure and

development from a image, and probably need a

vacuum frame and darkroom equipment to be used

properly.

Comments Welcome!

4

The main motivation for making ones own PCBs is the time saved. It’s also cheaper, of course. By making my own PCBs I can have one in my hands in about 30 minutes. The quickest I can get a PCB made by one of my suppliers is their 24 hour service, which means that I get it three days after placing the order.

Leon

5

I’ll second Leon’s comment that it really isn’t needed. Doing it yourself adds a lot of complication to the process too. I tried it, just for “fun”, and had a hard time getting the process working well. It also makes a ~30 minute job of making a PCB into a 2 hour job, if everything goes well. When it’s done, I’ve got a very nice functional solder mask, but the color doesn’t look as good as the pre-made boards, and I still don’t have that fancy white silkscreen. There’s a guy that sells small quantities of solder mask if you want to play with it [here.

My recommendation is to start with either toner transfer or using presensitized photo resist PCBs and start making stuff. Laminating your own resist onto the PCB or using a liquid photo-resist just adds another step where you can ruin an hour’s worth of work by letting a fleck of dust get trapped in the wrong place. If you want the boards to look great, send them out to be professionally made once you have an ugly working prototype. Or just put them in opaque project boxes :-)](http://www.pcbhobbyist.com/)

6

ditto about not needing a solder mask.

However, a solder mask can be quite beneficial if you are using solder paste (hot air, skillet, …). The mask prevents the solder from flowing, causing it to “bead up” which then causes the chips to self-align. With the correct amount of paste, the mask also prevents solder bridges.

7

From a half-professional, half-hobbyist standpoint, there’s three reasons I do or don’t use soldermasks:

  1. Environmental protection. The soldermask covers the traces, preventing corrosion and (in poorly assembled devices) damage or shorting by debris in the enclosure.

  2. Solderability. With practice, it’s easy to solder fine-pitch parts by hand with no soldermask. If you’re doing an automated assembly of those same parts though, using a soldermask is probably a good idea. It helps you get repeatable, reliable results.

  3. Aesthetics. It just looks cool. A soldermask and a [good silkscreen, although electrically insignificant, will boost ‘confidence’ in the PCB. The classic stereotype of a ‘good’ PCB is forest green with white lettering, and to someone who’s not concerned with the functionality of the circuit, a PCB like this will sell over a bare-copper PCB.

I’ve never tried to apply a soldermask myself, but from what I hear, you’re better off leaving it to a boardhouse to apply it.](http://forum.sparkfun.com/viewtopic.php?t=11423)

8

bigglez:

bobtron3.2:
What is the stuff, anyway?

Solder mask (AKA solder resist) is a protective layer on

the outside of PCBs to assist in wave soldering. It also

provides environmental protection for the PCB metal,

and improves the readability of silk screen legends.

I know what it does. I wanted to know what it’s made out of.

…

There are two reasons that I want to make my own PCBs:

  1. I like doing things myself whenever I can.

  2. Microchip has zero PIC18’s in DIP packages in stock right now. As it seems to be the trend for most everyone to use SMD these days, I’d like to break away from my dependency on DIPs.

If I’m going to make PCB’s I’d really like them to look good. That’s the biggest reason that I’d like to use a solder mask (just about the only reason). And I really don’t want to outsource my boards. It’s way more satisfying to make something yourself than to have someone do it for you.

Anyway, guys, I know that I don’t need a solder mask, but I’d like to try my hand at it. Thank you, emf, for the link to the UV resist solder mask. I think I’ll try that. I would be interested in something that can be silkscreened on to the boards, though. Ha ha, use opaque boxes! :smiley: I know I can do that…

9

Greetings (Still No First Name Supplied),

bobtron3.2:
I know what it does. I wanted to know what it’s made out of.

Someone already answered that question for you:

bigglez:
Some resists are lacquer or epoxy based liquids that

are silk-screen printed. Other types are the liquid

photoimage solder mask (LPSM) inks and dry film

solder mask (DFSM).

It helps to read the entire thread before editing...

bobtron3.2:
There are two reasons that I want to make my own PCBs:

  1. I like doing things myself whenever I can.

  2. Microchip has zero PIC18’s in DIP packages in stock right now. As it seems to be the trend for most everyone to use SMD these days, I’d like to break away from my dependency on DIPs.

Perhaps you should ask a local PCB house to give you

a tour. I think you’ll quickly see that their operation is

not adaptable to the hobby level. It’s unlikely you can

get the same results on your own - which appears to

be an important goal of yours.

While you’re at it, why not package, test, and mark your own ICs?

Comments Welcome!

10

bigglez:
While you’re at it, why not package, test, and mark your own ICs?

It’s been done. You should not underestimate the ability of a creative individual. I can think of one superb example:

“Chip Gracey designed the Propeller chip completely from the ground up, a feat rarely attempted in a world where most products are based on some excisting prior art, reference design, or chipset.”

-Make Magazine, Volume 10, Pg. 81, under the header ‘Silicon from Scratch’.

On the opposing page there is a quote by Chip himself regarding the process of designing his Propeller chip. I don’t think I could say it better myself:

“What I liked about what I was doing, was doing it. What was making me happy was the learning and the creativity.”

This individual not only packaged, tested, and marked his own ICs, but also, by his effort and persistence, the development of his own original ideas into a real, usable, successful microcontroller completely unique from all others, became real. According to you, this I suppose should not have been possible. Apparently, the concepts of entrepreneurial spirit and engenuity are lost on you.

-Robert H.

11

Greetings Robert,

bobtron3.2:
According to you, this I suppose should not have been possible. Apparently*(sic),* the concepts of entrepreneurial spirit and engenuity*(sic)* are lost on you.

Wasn't your OP about DIY solder masks?

Review the thread and you’ll see that your OP questions

were answered to the best of my ability. I would not attempt

home PCB fabrication (again) but I know that many hobbyists

do turn out functional boards often.

Once you’ve had quick turn pro quality PCBs (or slow turn

BatchPCB quality PCBs) you may find you’re time is better

spent on other tasks.

Comments Welcome!