Issue link: https://iconnect007.uberflip.com/i/1161956
30 SMT007 MAGAZINE I SEPTEMBER 2019 Naisbitt: It should be used correctly as a pro- cess, step by step; it shouldn't be done just at the end of the line. Matties: As the cleanliness test is currently. Naisbitt: Bingo. And that's where there are some problems that need to be addressed. Matties: By the time you're at the end of the line, it's too late. Naisbitt: Exactly. If you're making 1,500– 2,000 circuits that go into a particular aircraft or spacecraft every year, it's easier, in some respects. But if you're producing that num- ber every hour, that's a fundamental change of concept. We need to have a go/no-go answer as fast as possible. Matties: At the earliest possible point. Naisbitt: Right. So, the primary driver now is what else we could do that can determine accept- able conditions for a product to ship. All of the other techniques—such as ion chromatography, ROSE (resistivity of solvent extract) testing, which I hesitate to use that term, maybe even FTIR—are not able to evalu - ate the influence of non-ionic matter, which is a problem. All of the research that we've been involved with for the last 25 years shows that modern- day chemistries include additives regarded in the broadest possible sense as surfactant addi - tives. They're non-ionic, so they're not mea- surable nor detectable, and these additives are used for wetting or de-wetting depending on their application. To ensure that you can lower the surface energy of the material—such as solder fluxes as the primary objective at this stage—how do you get it to stick on the under - side of a board if you don't have solids? You use these additives as wetting agents and have an excessive amount of liquid stuck on the ceil- ing above you. How does it stay there? Amaz- ing! But then the problem is that all of this liq- uid has to be neutralized or dealt with. And to that extent, it's not unusual to find the operator turning up the temperature to drive off these residues. However, with any - thing that gets hot tends to expand, the surface of a circuit board resembles a sponge. Now, you have trapped residue subsurface, which is an entirely separate issue. Insulation resistance testing on the subsurface was first conducted— based on my knowledge and all of the research that I've been involved with—by Laura Turbini, originally of the old AT&T Bell Labs. The other task techniques then come into their own to identify what is there that's caus - ing the problem. The two go hand in hand. What I then have to try and do—and I'd like to say that I've been successful in achiev- ing it—is initiate a new test method called process ionic contamination test- ing (PICT). I've done it for one sim- ple reason. ROSE testing has been around since the '70s and the industry is totally entrenched with it. I won't live long enough to see necessary changes, improvements, and enhancements made to the ROSE test and have it be acceptable to every - body. So, let's start again. And as I said at a conference in Chicago in 2016, is a ROSE still a ROSE when it's PICT? That's what's happening. Now, our new CTO Emma Hudson is the vice-chair of the 5-32a (Ion Chromatography/Ionic Conductivity TG and 5-32c Bare Board Cleanliness Assessment TG). PICT displacing ROSE seems to be the logical development. Matties: So, the standard for the chemical clean, like with Bosch, is there a new standard now? Is this being approved and adopted, or where is it in that process? Naisbitt: With the input from a huge number of people, I've put together a document that has now been accepted by IEC. It has gone through all of the necessary approvals. Hope- fully, it will be scheduled for publication at the end of this year.