Issue link: https://iconnect007.uberflip.com/i/976095
38 SMT007 MAGAZINE I MAY 2018 were reached by that subgroup. First, the ROSE test should no longer be referred to as a cleanliness test, but as a process control tool. This was a reasonable conclusion since ROSE was never meant for cleanliness as industry had defined it. Second, users of the test must provide objective evidence, aside from just ROSE alone, to show that their manufacturing process is in control. More information about what the subgroup defined as "objective" evidence can be found in IPC-WP-019. The statement made in the title to this article is where we want to focus most of our discus- sion. We are in the camp that believes the ROSE test provides little value for evaluating today's assembly products and here's why. The first significant concern with the validity of the ROSE test is the solvent. Back when the test was developed the predominant flux being used was heavily comprised of rosin (>30%). The 75/25 mixture was a very effective solvent for break - ing down that flux and bringing it into solution. This is an important factor to consider because to accurately measure the amount of residual flux on a PCBA, you must first have a solvent that can dissolve it into solution. This is one of the major problems with the ROSE test today. Why is the solvent an important consider- ation? Typically, four questions that are asked when performing cleanliness testing of assem- blies. The questions are as follows: 1. What types of residues are on the surface of the assembly? 2. What are the concentrations of those residues? 3. Do those residues/concentrations pose any risk to product performance/function? 4. Where are the residues originating? To have any hope of answering these ques- tions, we need to consider a testing platform with two very specific attributes: selectivi ty and sensitivity. With the advances in board design, product miniaturization, process improvement and the myriad of chemicals used in assembly production today, a bulk-solvent measurement is not adequate for determining if there are any hidden residue traps. Next, the ROSE test uses far too much solvent for an accurate test. This is a problem because too much solvent has a diluting effect that causes any extracted residue to be lost in the noise of the system. The solvent volume is a major consideration for residue evaluation because we need to get a more concentrated representation of what is on the surface. In the real world, failures rarely result from liters of liquid contacting the assembly. Quite often, all that is needed are droplets, and in some cases, only humidity. Now to the issue of using the ROSE test as a process control tool. Before we discuss this any further, we must first define "process control" The following, taken from www.businessdic- tionary.com, suits this discussion the best: "Activities involved in ensuring a process is predictable, stable, and consistently operating at the target level of performance with only normal variation." Figure 1: The ROSE system. Figure 2: Ion chromatography apparatus.