Defect of the Month with Bob Willis – Cleaning Compatibility

Hello, my name’s Bob Willis, and welcome to Defect of the Month. Every month I take the opportunity of looking at process defects as I have for the last few years, and provide a video explaining one of those defects. Hopefully you’ll find it useful and interesting, and of course, pass on information to some of your colleagues. I’d just like to talk about Cleaning Component Compatibility.

It’s very important that if you are going to clean products prior to conformal coating or clean products because you’re using an activated flux or possibly a customer wants you to clean their product, the important thing is you should confirm that all the components and the materials you are going to be using are compatible with the total cleaning process. The product designer is the guy who should make that happen, hopefully. If not, you as the process engineer need to confirm the components are compatible

Surface mount part construction are more likely to be compatible with cleaning materials, however they do bring their own challenges when setting up effective cleaning under parts.

Loss of component coating during cleaning, it did not impact on the component operation

So you must know what cleaning material or process is going to be used and test components. It’s not necessarily good enough to just accept the fact that a component supplier has said the components are compatible in their specification. You must prove it because you want to know that you’re not going to experience failures. Over the years, I’ve tested many, many components for cleaning compatibility with water, with semi aqueous and of course solvent cleaning systems when we used those high volume inline cleaning applications. A lot of people take it for granted that components are compatible. Well, that’s not necessarily the case. There are the obvious things, which probably are compatible, which are surface mount components. So if we are looking at BGAs, QFPs, QFN plus chip resistance and capacitors, all these parts generally are compatible, they’re sealed. There should not be any impact as long as the cleaning process is in control

Significant damage to the coating on this chip component

However, it’s more likely to be through whole components that may have issues. So fundamentally, you want to look at the component to make sure there’s no openings. If it’s an electro mechanical part, then it must be fully or temperedly sealed in some way to prevent any liquid getting inside. Because if you are using, for instance, a semi aqueous process that’s mildly acidic before you use the aqueous part of the process to clean it and leave it in a neutral state it can corrode. You don’t want anything getting in a seal component anyway, because whatever material penetrating in may affect the operation of that particular part. One of the simplest ways of confirming compatibility of components, particularly through whole parts, is weight gain, weight loss. You first determine the cleaning material, the cleaning cycle time you’re going to be using, and then you test some parts , perhaps five or six parts

You weigh them very accurately. First of all, you put them through the process and then you weigh them afterwards. You can of course, simulate this in a laboratory situation with a beaker of the test fluid, the fluid you’re actually going to be using at the temperature you’re going to be using it at and submerge the parts. If its ultrasonic cleaning, then there really there needs to be some ultrasonic agitation within your test set up. So you weigh the parts to start off with. You reweigh the parts after the cleaning and drying part of the process is complete and see if there is any weight gain. That’s a pretty easy way of finding out. Some solvent and semi aqueous cleaners have been seen to attack some plastics and need to be checked. A couple of other things to look out for are markings being removed or nomenclature on PCBs plus anything else that may change like solder mask color due to absorption

Incomplete solder paste reflow caused by solvent absorption in solder mask

Solder mask absorption with any solvent is particularly an issue. If you’re going to clean a board, then you are going to print solder paste straight away. The material that’s been absorbed by the mask may affect the successful reflow of the paste.  (Watch Bobs video on Non Reflow of Solder Paste)  Component compatibility, please think about it, it’s logical, but really it’s the purchasing and design team that must define component compatibility requirements with the assembly process. When you are a contract manufacturer, it is a little bit more difficult, which I’m sure you’ll understand, but please make sure your test parts, check parts or get confirmation they’re compatible with your process from the customer. If you enjoyed this video, please subscribe to the channel, like the video, and of course, ring the bell and we’ll send you notifications of any new videos that are released. My name’s Bob Willis, and thank you very much for tuning in for Defect of the Month