Issue link: https://iconnect007.uberflip.com/i/1415897
OCTOBER 2021 I SMT007 MAGAZINE 79 In addition to solvent extract, another test method that has been used extensively is surface insulation resistance (SIR). the visible residue requirements are established between Manufacturer and User." e bottom line is, IPC leaves it up to us- ers and suppliers to establish mutually accept- able requirements based on the applications for their products. e standards also provide some references and white papers for addition- al guidance that users and suppliers may decide to use to establish their requirements. What it boils down to is that different users and suppli- ers can have different cleanliness requirements for the same applications and same products. I am not sure if that is a good thing. My Views on Cleanliness Requirements As discussed above, IPC does not tell you what the specific cleanliness requirements should be. But it does give a roadmap as to how to go about establishing the requirements. As noted earlier, IPC does have some very specif- ic requirements when it comes to visually ac- ceptable residues such as flux, white residues, and foreign objects, things you can visually see. However, when it comes to specific clean- liness requirements such as surface insulation resistance or micrograms of solvent extract re- quirements, you are on your own. Many would argue that the solvent extract test is relevant only for rosin. at must have been the reason for making the change in the J-STD-001, going as far back as 2005 when re- vision D was released. Now, more than 15 years later in 2021, we have revision H and the re- quirements for cleanliness are the same even though we have now more widespread use of components with practically no gap between the bottom of the component and the top of the board. But what have we been doing for the last few decades, starting in the 1980s? You guessed it: Solvent extract (aka ROSE), and I am talking about this test being used for all kinds of fluxes and all kinds of applications. In addition to solvent extract, another test method that has been used extensively is sur- face insulation resistance (SIR). Previously, the industry used aggressive water-soluble fluxes; an SIR value of 500 MΩ/square (per square and not per square inch) on a pro- duction board under chip components, on a sampling basis, was the acceptance criteria. When I was at Intel, this test helped us dis- cover many problems, such as poor adhesive cure profile that was trapping flux due to voids in the adhesive. We also had to make sure we didn't ship any product with corrosion poten- tial in the field. e argument for not specifying a cleanli- ness requirement for RE and OR fluxes is that you cannot possibly develop acceptance cri- teria with repeatable test methods when you don't really know what kinds of substrates, sol- der masks, and coatings these fluxes will in- teract with in some unknown environment. is argument may be valid, but we can ask the same question when it comes to RO flux- es. Besides, this problem can be solved by be- ing more conservative and accommodating RE and OR fluxes in a very humid environment, as we have done for R0 fluxes. We can make an exception for applications where you are send- ing a manned mission to Mars, and you can af- ford to do all kinds of tests in the book if you are using RE and OR fluxes. But we are not all sending the assemblies to Mars. If you are going to have a corrosion problem, does it really matter which kind of flux it came from? For example, you can have a corrosion problem from rosin flux if you use it generous-