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Hey, how about this global pandemic? Wild stuff. I am going to attempt to find a silver lining among the many dark clouds, and I am willfully overlooking the health issues and focusing on electronics with this month’s installment. This makes sense, as I am not a medical doctor, but I have diagnosed more than a few ailing electronic assembly processes.
A few months ago, we started seeing delays in shipments from many of our offshore partners as they had to do the right thing and close their facilities for the greater good. We knew at that time that it would set off a chain reaction of availability issues for everything from silicon wafers and bare PCBs all the way to final production assembly for the end-user.
This has forced many companies to take a hard look at how and where their parts and assemblies are sourced and see what other options are available going forward to help deter this same situation from happening again if another round of global closures took place. Many companies willfully placed all their eggs in a single basket while wearing rose-colored glasses and, to this point, it probably worked out fairly well. Today, we are hearing many of those same companies are looking to expand their supplier base, and with that, the possibility to rethink how they approve suppliers is born. Thanks, COVID-19?
Let’s start where most things start—from the beginning. When I say “from the beginning,” I mean from the suppliers of all the materials you use to build your assemblies. This list should include your PCB fab shops, component suppliers, solder paste and flux, adhesives and coatings, connectors, housings, and the list goes on. As I have mentioned about two million times, everything you use in the assembly process brings with it an inherent risk of contamination that can affect your product’s reliability. When working in the Class II and Class III worlds, we all know that reliability is as important as it gets, so it’s paramount to take this opportunity to be sure you are getting what you need regarding cleanliness.
The first thing I recommend is looking at your current requirements and then determining whether they are still applicable to what you are building today. Many times, those requirements were based on a product that has gone through a series of minor revisions over the years. When looked at individually, these changes seem small, but collectively, they have substantially changed the assembly. To me, that means the original set of building blocks may or may not be working the same as they did initially. They may still be working to the point that the product functions as it leaves the building, but go back and take a look at the pile of “no trouble found” returns and figure out the root cause from there.
Many times, you’ll discover that while the materials may not have changed, the way they are being used has. This is why it’s a great idea to take a look at qualifying new suppliers with updated acceptance criteria. For instance, many suppliers have been contractually obligated to test cleanliness using the IPC standard for cleanliness that was found in J-STD-001 but has since been removed. Since the test has been determined to be inadequate, it’s time to develop your own testing plan specific to your product. That test may still include ROSE testing and the acceptance criteria of 1.56 µg of sodium chloride equivalence, but that can’t be determined until you have a larger data set that includes SIR testing for objective evidence.
IPC-WP-019 has all the information on this important (and some say drastic) change and what is recommended going forward. At a minimum, you should ask for ion chromatography testing for initial acceptance and then possibly on an annual basis as well. For all the interim shipments, you should be able to accept ROSE testing on materials like bare boards; but again, only if that is backed up with IC data.
It is also a good idea to ask for similar data from your component suppliers. Many component assembly processes use the same plating processes as a bare board and can leave the same type of detrimental residues. When a component has plating residue, it can migrate up the leads into the body of the part and corrode wire bonds, among other failures. Package-on-package (PoP) components can leave all the same residues as a standard assembly process, so think of them more as tiny assemblies instead of components.
Speaking of assemblies, let’s discuss what you should be asking for on those. When you look at the witches’ brew of chemistries used to get us to this point, it is a miracle they haven’t simply melted into a pile of electronic goo. I assume that is how the electronic pioneers came up with the formulas that we use today; if it melted, back it off 10%, and try again.
Again, historically, cleanliness per the IPC was covered with the simple, quick, and inexpensive ROSE test. Per IPC WP-019, “This test methodology was originally developed in the 1970s; it was never intended to be used as a cleanliness test, nor as a test for product acceptability, it was only intended to be used as a process control method.” Unfortunately, this test has been used for product acceptance for many years, and that’s not a good thing. I won’t go into all the reasons why, but there is a mountain of studies out there for review.
For years, our lab recommended that customers build at least 20 assemblies, then test half with ROSE and half with ion chromatography. This gives you a rough correlation to figure out what your ROSE number needs to be—whether that is 1.56 or 156.00—as it is all based on the way the specific ROSE tester reads your product. Many large companies have gone the extra step of not only doing full board extractions for the IC test but also looking at specific areas of the PCBA to determine how clean it is.
Global extractions with either IC or ROSE will normalize out pockets of contamination across the full surface area of the assembly and most often results in a passing grade. A full board has never failed in the field; it’s always a specific component or soldering process. Thus, it’s important to know exactly how clean each individual process is to better address and optimize that and reduce the levels of active residues. These types of tests are being seen on more prints for new products but not
being applied to legacy products due to existing contracts.
If you are planning on qualifying new CMs, this is a great time to revisit some of those legacy products and update the cleanliness criteria as if it were a new product. Of course, this applies to all the acceptance criteria for all types of testing and not just cleanliness. If you have a product that has been in the field for a few years and there is a trend on the failures, there should be a way to better screen for that in first article builds. While your company is taking this unexpected opportunity to expand your supplier base, you might as well expand your acceptance criteria to help produce a more reliable product.
Now, go wash your hands.
This column originally appeared in the July 2020 issue of SMT007 Magazine.