SMT007 Magazine


Issue link:

Contents of this Issue


Page 21 of 99

22 SMT007 MAGAZINE I AUGUST 2018 Cleaning a no-clean flux is not a task for the uninitiated or uneducated; it is a task for those who like to run into brick walls with blindfolds on. It can be as fun as it sounds, or with the proper knowledge and a little experience, it can be merely terrible. There are a few reasons to choose to clean a no-clean flux (and even fewer are actually good reasons). One good reason to clean is when the assembly requires conformal coating, especially when using Parylene. Another reason is when probes are required for testing. The flux residue can inhibit a good contact surface. Other than that, I struggle to think of another good reason to clean a no-clean flux. From where I sit here in the failure analysis (FA) lab, the main reason for cleaning no-clean is that if flux residues are not fully removed, what is left behind will be of no concern since they were intended to be left fully intact to begin with. As an employee at an analytical test lab with kids to send to college, I couldn't agree more—no further research is necessary. As an objective observer, there are several problems with this theory (which we will touch on in this month's installment). Let's start with a brief explanation of no-clean flux. Traditional water-soluble flux formulations have approximately 10–40% solids. Flux activators at these levels might burn through the containers they are shipped in if not used within a week or two after receiving them, so they need to be cleaned right away. These residues can be effectively removed with a standard in-line wash process using only high-quality deionized (DI) water, or with the addition of a saponifier to lower the surface tension to get under low-standoff components Quest for Reliability Feature Column by Eric Camden, FORESITE Cleaning a No-clean Flux: The Worst Decision You've Ever Made?

Articles in this issue

Archives of this issue

view archives of SMT007 Magazine - SMT-Aug2018