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Electronic Assembly Rework Best Practices: No-Clean and Cleaning Conditions
Materials Tech |
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Authored By:Zach Papiez, Matt Imburgia, and Mike Bixenman Magnalytix, LLC TN, USA J.D. Buller Air-VAC CT, USA SummaryElectronic Assembly reliability must consider process residues and cleanliness. IPC J-STD-001J—Section 8 requires assemblers to qualify soldering and/or cleaning processes that result in acceptable levels of flux and other process residues. Multiple soldering steps are used to build the assembly. The SMT process is considered the most stable and repeatable. Secondary processes, such as rework, add variability to the assembly process. Flux residue is a common concern when reworking the assembly. Flux can wet and spread outside the area where the rework is taking place. In addition, topical cleaning after rework can also wet and spread active residues outside the area where the rework is taking place. Device failure can occur if these active residues are exposed to climatic conditions. This research aims to study the electrical effects of flux and process residues following the rework process. Manual soldering, as compared to the use of a rework station, will be evaluated. This study aims to define best practices for assemblers who build to either a No-Clean or Cleaning condition. ConclusionsSecondary soldering processes have a higher risk of ECM failures. Manual and rework soldering are less controlled processes that increase process variability. From a test lab perspective, we find more failures resulting from rework. The test data from the designed experiment used for this paper were relatively good, which could give an engineer confidence that rework is relatively safe. Rosin flux that is fully heat-activated is benign. Topical cleaning leaves and spreads residues. When exposed to climatic conditions, there is a high risk of failure occurrences. Operators often use water-soluble flux because it is easier to clean. However, unless cleaned using an aqueous cleaning process, the residues transferred across the assembly will fail quickly. We highly recommend using the best practices we documented in this paper. These practices should be documented and operator trained. Validating and qualifying these practices using SIR, C3, and IC is highly suggested. Initially Published in the SMTA Proceedings |
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