Issue link: https://iconnect007.uberflip.com/i/1415897
78 SMT007 MAGAZINE I OCTOBER 2021 of the major points in the standard (IPC-A-610H and J-STD 001H). "Unless otherwise specified by design, or by the User, the acceptability of the residue condition shall be determined at the point of the manufac- turing process just prior to the application of con- formal coating , or on the final assembly if con- formal coating is not applied." e requirement is essentially based on pro- cess control parameters, since changes in man- ufacturing materials or process parameters may detrimentally end item residue levels and product reliability, which may necessitate re- qualification. Manufacturing materials and/or process changes fall into two categories: major or minor, with major changes requiring valida- tion, and minor changes with supporting ob- jective evidence. Qualification testing is generally considered to be more extensive in nature. Minor changes with supporting evidence are generally lesser efforts, involving shorter duration SIR tests or focused chemical characterization tests. Again, the standard specifies that the degree of process change and associated required no- tifications of change are le to be established between manufacturer and user. However, IPC does provide some practical guidelines as to what to do. Here are some examples: 1. You should not have discernible residue, but flux residues from no clean fluxes are acceptable. 2. However, flux residues that inhibit electrical testing or visual inspection are not acceptable. 3. Similarly, dull appearance is acceptable but colored residues or rusty appearance are not acceptable. 4. Any foreign objects that potentially may be conductive are not allowed especially if they violate minimum electrical spacing requirements. 5. White residues which may contain chlorides and cause corrosion are not acceptable. Here are some more guidelines in the stan- dard: "Unless otherwise specified by the User, the Manufacturer shall qualify soldering and/or cleaning processes that result in acceptable lev- els of flux and other residues. Objective evidence shall be available for review. e use of extrac- tion testing , i.e., ROSE, IC, etc., with no support- ing objective evidence shall not be used to qualify a manufacturing process. Supporting objective evidence shall be test data and/or other documentation demonstrat- ing that the performance of the actual hardware is not adversely affected under conditions an- ticipated in the service environment. is may include: 1. Surface insulation resistance (SIR), possibly in combination with ion chromatography testing , to demonstrate acceptable levels of residue. (Author's note: However, no specific value is mentioned as to what the SIR value should be. I will provide some numbers as to what that should be based on historical data as to what you can expect if you follow some common process control.) 2. Historical evidence, including field returns, warranty service records and failure analysis, demonstrating that ionic and other residues on delivered products have not caused failures in service. 3. Electrical testing results, with power on, during extremes of temperature and humidity, which simulate the end use environment. Electrical failures should be subjected to failure analysis to determine whether ionic or other residues have caused the failure. This testing may occur during product qualification or outgoing acceptance testing. Rework processes shall be included in the process qualification. When it comes to visible residues, the require- ment is that assemblies subjected to cleaning pro- cesses shall be ee of visible residues. However,