Can Solder Mask Be Considered an Insulator?



Can Solder Mask Be Considered an Insulator?
Is solder mask considered an insulating material and not a defect if proven the solder mask has dielectric withstanding voltage greater than 500 volts? Is solder mask considered a durable insulator over time in harsh environments? The Assembly Brothers, Jim Hall and Phil Zarrow, address these questions.
Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up
CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
Phil Zarrow
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.
Jim Hall
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.

Transcript


Phil
And welcome to Board Talk. This is Jim Hall and Phil Zarrow, The Assembly Brothers, here to talk about assembly process, situations, problems and ideas. Today, Jim we have a question about solder mask.

EC writes, if solder from a printed through-hole lead on the source side touches solder mask that is over a copper ground plane, but not electrically shorted is this a defect per IPC standards due to violation of minimal electrical clearance? Or is solder mask considered an insulating material and not a defect if proven the solder mask has dielectric withstanding voltage greater than 500 volts? Is solder mask considered a durable insulator over time in harsh environments?

Jim
EC, I am sorry but I have never heard the term source side referring to one side or the other of a plated through-hole printed circuit board. Solder side, component side and so forth. I am going to assume that the source side is the solder side, the side that comes into contact with the wave or the selective soldering or the hand soldering.

Phil
Something new everyday. We hear new terminology everyday in this wonderful industry. I agree with Jim’s logic on that.

Jim
Solder mask is certainly an electrical insulator. Can it withstand 500 volts? Well, it depends on how thick it is. The point I want to make is most of us are using liquid photo-imageable solder masks. The thickness is not necessarily consistent over the whole board. Guaranteeing that it is thick enough at this particular point to withstand 500 volts is kind of hard to determine. But I want to back up and go to a more fundamental thing.

If you have solder spreading from a through-hole joint, the way you have described it here, it is off of the pad, beyond the annular ring around the through-hole and it is past any gap onto some other trace on the board that has copper on it. That is a lot of solder spread away from that through-hole joint. I question whether that is really desirable and whether it is really acceptable in terms of too much solder spread.

Phil
This goes with regard to workmanship standards in general. Certainly, in this situation workmanship standards should be in agreement between you and your customer. I can hear a lot of 610 aficionados snorting and harumphing. The bottom line is 610 is, as good as it and comprehensive as it is, it is still basically a generic specification.

Again, what is acceptable for the environment, the application of the product that you are using should show what can be allowed and what can’t be allowed if there is something that is not clearly defined in 610 or if you are attempting to deviate. Check with your customer. Check with design engineering in terms of what this board is going to be living in. Will it work?

Jim
EC specifically says durable insulator over time in harsh environments. When you are talking harsh environments, the hair on the back of my neck goes up. Probably no, but you should confirm it with your customer.

Phil
So, on that ominous note you have been listening to Board Talk. We look forward to what our readers and listeners write in. But in the meantime, regardless of how well your solder mask has been laid down whatever you do don’t solder like my brother.

Jim
And don’t solder like my brother.

Comments

We had a similar question in regards to clinched leads violating minimum electrical clearance. Our conclusion is that it's not acceptable.
Dale Carmine, Reinke

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