The month's topic for SMT007 Magazine is "Selling Your Services: A look at strategies to help you improve how you sell your electronics manufacturing and PCB assembly services." This is a topic I can speak to regarding quality and how testing can be a selling point for your product based on how many times I have seen field failures here in the lab.
Think about it. If you are shopping a new product around to multiple CMs, and if all other things in two separate CMs are equal including price and delivery times but one offers a more comprehensive ongoing quality monitoring system, why wouldn’t you go with that one? I realize that you usually pay some type of premium for the CM that has an overall quality monitoring system that goes beyond just ICT or bench level testing. Most CMs will give you some sort of assurance that the product is working as it leaves the facility, but if one has a mindset that more than basic testing is required to show reliability, you will more than likely have fewer field failures.
This is something we see from many CMs in the form of a more expansive upfront set of testing at PPAP that translates into a more meaningful ongoing monitoring strategy that relates back to the original set of tests that shows the product will operate under harsh environments. If your product ends up in an automobile cabin or other controlled environment, all the better. Often, what we see with field failures are they come from a CM that is doing nothing more than checking a box. If there isn’t a specific cleanliness requirement, the default is often to perform the historically accepted test that simply does not line up with today’s technology demands.
The old way of looking at cleanliness and how it impacts reliability was based on 1970s assembly procedures and materials, and may or may not have even been fully effective for that time. As components continued to shrink over the last 40 years, the acceptance criteria didn’t adjust as it should have. One reason for this is the group of people with the mindset that, “This is how we have always done it, and change be damned, it’s how we are going to keep doing it.” Guess what? People used to die all the time from polio and tuberculosis, but as medical science advanced and people embraced vaccinations (except for Jenny McCarthy of course), those diseases are a thing of the past.
Now, I am not saying that a dirty PCBA is as dangerous as TB, but my larger point is that scientific advances are allowing us to make smarter choices in terms of adopting a quality strategy. Too many times I see an assembly print without any reference to cleanliness or only the default of IPC, which is super vague as there are 200+ test methods and only a few related to cleanliness. The saying “you get what you ask for” comes to mind. It is so important to demand and clearly document cleanliness requirements and verifications on a regular basis to help mitigate cleanliness related issues in the field.
So, what is a good strategy to maintain quality related to cleanliness? Here in the lab, we love the customers planning new product to test bare fabrication, components, as well as first-run production with ion chromatography. That is the first and easiest way to see just how clean each of those sample sets are before you go into full production. IC analysis gives you a good picture of the type of ionic residues present on each sample, and each of those ions can be traced back to a specific part of the process.
With that information in hand, and when necessary, you can go back to the supplier, review their process, and see where it can be optimized to reduce residual ionic content. After optimization, a second round of testing is in order to see the effectiveness, and then further optimize from there. Component manufacturing and bare boards share a lot of the same risk due to the plating processes, which use highly active chemistries. Those chemicals need to be fully removed or effectively neutralized to a low enough level that when they arrive at the CM, they won’t be the root cause of assembly failure down the road.
Many PC fabrication shops aren’t using the best quality DI water for rinsing after plating because good DI isn’t cheap. The higher-quality wash or rinse water uses lower the surface tension. Lower surface tension allows the DI water to penetrate into vias and remove process residues better. In past studies, we have found that tap water is incapable of penetrating vias smaller than eight milliliters, which are ever present on today’s PCBAs. We found one supplier that was using water directly out of a nearby river. I can’t make this stuff up. The print didn’t have any cleanliness specification or direction for proper washing after plating, and the customer was more than thrilled to save a few cents per board with no questions asked. When the boards were used for actual production, the customer had massive amounts of failures, and the cost of replacements couldn’t be pushed back on the supplier because they got what they asked for—nothing.
This company was an obvious outlier in the big picture, but it goes to show that you can’t rule out anything if you don’t have a rule in place. The strategy here for the PC fabrication shop would be to pay a little more for a good quality water system that can maintain at least 10-megohm resistivity DI water for more effective wash and rinse processes. If they have that, and the shop down the street is using a one-megohm dummy light, you can pretty much guarantee that the shop with a better water system is supplying you higher quality bare boards. Bare boards are the basis of your final product, so if you start with better quality boards, you will ultimately have higher quality final product. As previously mentioned, the component manufacturers are up against some of the same issues in terms of removing plating chemistries, so the same recommendation for water systems applies here. There isn’t a lot more you can test with bare boards regarding cleanliness, but having a quality system in place for every customer can put you in front of your competitors without a doubt.
When it comes to the CM and the actual assembly process, there are more tests you can add to your overall quality system to help give you the edge over your competition. You can start with using suppliers that perform tests previously mentioned that show you’re using quality parts and boards. This is especially important when using no-clean flux for the production as there is not a final wash process that can help remedy the sins of your suppliers. IC analysis is still the gold standard for determining the exact type and amount of ionic residue present on final assemblies, but that is also expensive and not realistic to have in-house in most cases. A few of the larger CMs do have IC in-house, and when used for process qualification and monitoring instead of just failure analysis, it can really help put them in their own league.
As part of an assembly house’s cleanliness strategy, it is important to understand that overall ionic cleanliness is one thing, but looking at specific locations on an assembly is even more important. The reason that is true is that when you have a failure, the entire assembly doesn’t fail but a single point related to a single process or part does. Knowing this you can separate each assembly process, better determine which one is the culprit, and be able to do it much faster than any full board analysis. Being able to distinguish reflow from wave from hand operations is crucial when you are looking to qualify and monitor an assembly process. Looking at each solder operation as part of an overall quality system allows you to control cleanliness better.
When you are testing PPAP samples, we always recommend some sort of environmental exposure testing along with IC test to help correlate performance under elevated heat and humidity conditions. What this additional test does is show that whatever level of residues you have on your product after assembly won’t cause electrical leakage related issues, and you will have IC levels to correlate to. When going into full production process monitoring, IC is much faster than a 168-500 hour environmental exposure test. Monitoring specific location cleanliness can be done in several ways. Doug Pauls from Collins Aerospace and I released a presentation at the High-Performance Cleaning and Coating Conference in 2012 that detailed about a dozen different ways to perform localized extractions for IC analysis.
I’ve mentioned that this type of testing isn’t cheap, but when you compare the cost of proving you have a good, clean process against the cost of a wide-scale recall, it’s not even in the same ballpark. When you’re competing against other suppliers or CMs, having a better-quality system in place than your competitor will pay for itself many times over.