PCB007 Magazine

PCB007-July2019

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JULY 2019 I PCB007 MAGAZINE 87 real need out there. Most folks don't have ac- cess to Ph.D. materials scientists. If a company is able to employ a Ph.D. in materials science, they are usually down the hallway from your manufacturing facility and not working hand- in-hand with those on the production floor. We work with those people to bring about knowl- edge expertise and process recommendation to gain very high reliability where stresses, tem- peratures, thermal cycles, and contamination events are critical, and sometimes in defense or medical device cases, have to deal with lives. Shaughnessy: What is the threshold for the switching method for going between XPS and traditional and ion chromatography? How do you know which techniques to use? Kidd: C3 extraction and ion chromatography take a solvent and apply a very small amount to dissolve what you have on your surface. Then, you will use an ion chromatograph to look at what kind of species or ions you're seeing from what has been dissolved on the surface. That is a measure of what your solvent can dissolve. Using an in-situ spectral technique like infrared spectroscopy or XPS is a direct measure of the surface state. You don't have to worry about having some kind of solvent medium to dissolve the material. You're looking at what's there. It's a direct measure or a direct eye on the function - al groups that you have on those materials. Bien: Solvent extraction is more of a legacy method. You would use it in cases where you don't have access to spectroscopy. Kidd: Right, and for the C3 IC methodology, that does a good job at detecting conductive species, but it's not going to tell you if you have an organic species that has made its way onto your surface from some kind of environ- mental contaminant or upstream contact con- tamination event. It's going to tell you if you're chemical etch bath is leaving behind ions that would otherwise create a pathway to short-cir- cuit your board. It's not going to give you evi- dence of oil amount or if you have silicone or something like that. Shaughnessy: What are the biggest challenges that your customers are facing that you can help them with? Bien: Most folks have intermittent failures where they don't have any understanding of why this is happening now versus two months before when they made 500 boards in a run, and everything was great. In terms of the or- ganics that Elizabeth mentioned, the organic materials finding their way into processes are the reason for adhesion loss most of the time. There are three things that we need to con- trol to get reliable adhesion: (1) the chemis- try of the adhesive and the coating that we're putting down, (2) the chemistry of the surface that we're presenting to that adhesive, and (3) how we cure it in terms of temperature, pres- sure, environment, etc. Most people are doing steps one and three, but they're not taking a good look at step two. In terms of what we're seeing out in the mar- ketplace, it's a lot of things like wash processes that are dragging soaps and surfactants out of them and manufacturers not having good tech- niques to identify those before they send them into SMT process or conformal coating pro- cess. It's a breakdown somewhere in the chain of events that are in the manufacturer's proce- dural steps, from incoming component surface inspection all the way until final assembly. It could be in a wash process or plasma treat- ment process, but it's a failure of knowledge of how to tune the knobs. Kidd: And to that point, people are monitoring the knobs. In the case of a parts washer, they're monitoring the concentration of cleaning agent and particulate count, temperature, and cycle time. What they're not measuring is the actual surface that's coming out of that washer. For example, you could have a washer that has been recently cleaned and is in pristine condi- tion, passing all of your checks—including par- ticulate count and concentration analysis. And you could have a washer that has been running for a month, has the "correct" cleaning agent concentration, and is passing the particulate amount. But if the agent you're trying to clean

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