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
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
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
I don't know what IPC says, but I reject those when I find them for clearance concerns. The variables that concern me are whether the mask thickness is consistent and whether there are "pinholes" or bubbles in the mask. I worry more about the potential pathways for electrolytic corrosion which I have seen happen through masked areas many years ago. Solder touch-up is a quick fix which to my thinking is a lower risk than leaving the potential sneak path where it is. Prevention is a better solution, and I suspect a constant rotation of inexperienced manual solderers as a significant cause.
Andrew Stearns, Particles Plus
Unless stipulated, you should reconsider clinching as a process. We eliminated clinching in 2009 and have saved more than 40% in labor, eliminated the long periods needed to train a skilled operator in clinching and were able to make multiple improvements in our processes as a direct result of moving to preforming and insertion. Too many benefits to discuss here.
Charles Truter, Gallagher
Just for clarification, you are correct. The IPC-A-610H specification defines the 'Source' Side or more accurately the 'Solder Source Side' as the side of the printed board to which solder is applied. The Solder Destination Side is the side of the printed board that the solder flows toward in a through-hole application.
Rudolph Fulgham, Electrolux
The best thing in my mind would be to validate with the fab house what their minimum solder mask thickness is. Use that as your dielectric thickness. Also check what their maximum tolerances around solder keep outs are. Use those two bits of information (along with solder mask dielectric properties) to determine if it will withstand. I'd be very curious to know the application or use case. What other conductor is sitting near your solder surface that this might be an option. At the end of the day, the durability of the solder mask is probably gonna be the downfall of this idea.
Clayton, Industrial Protection
Solder is not going to flow unless it sees a path, I would recommend reworking to avoid potential short. Regarding clinching, IPC has the requirement to clinch away from non common conductor or maintain a minimum clearance.
Sundaram Kumaravelu, EIT
Just listened to the presentation and agree. If the soldermask is to be used as an insulator, it must have certain dielectric properties and the needs to be qualified before it is used for that purpose.
Leo Lambert, EPTAC
We had a similar question in regards to clinched leads violating minimum electrical clearance. Our conclusion is that it's not acceptable.
