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44 SMT007 MAGAZINE I JULY 2026 • Copper alloys • Kovar: Nickel/iron and cobalt alloy • Alloy 42: Nickel (42%) and iron (58%) • Alloy 52: Nickel (52%) and iron (48%) • Phosphor bronze: Copper alloy containing tin/ phosphorus • Beryllium copper: Copper with beryllium alloys Gold Coatings Understanding and distinguishing between gold flash and gold electroplate when evaluating compliance with J-STD-001 gold removal require- ments is important for addressing gold interme- tallic conditions. The concern with excessive gold thickness is the formation of brittle gold-tin inter- metallic compounds, reducing solder joint ductility and reliability. 5 Historically, connector contacts are plated with gold thicknesses ranging from 50–100 µins. However, increasing precious metal costs resulted in widespread adoption of thinner deposits commonly referred to as gold flash. Gold flash thickness is typically below 10 µins, whereas functional gold plating typically exceeds 25 µins. 4 Consequently, manufacturers should obtain plating thickness data directly from component manufac- turers and suppliers to minimize or eliminate gold embrittlement conditions rather than relying solely on descriptive terminology. Toe Fillets One common inspection-related question is whether a visible toe fillet is required for gull-wing solder joints. IPC-A-610 establishes requirements for side joint length, heel fillet height, end joint width, and solder thickness. There is no minimum requirement for toe fillet. 1 If the toe of the lead does not violate the minimum electrical clearance requirement, it is acceptable. The confusion arises because illustra- tions depict solder extending to the toe of the lead. From a structural perspective, the primary load- bearing region of the solder joint is the heel fillet, not the toe fillet. Therefore, the absence of a visible toe fillet does not impact solder joint reliability. However, IPC specifically states that written requirements take precedence over illustrations. Soldering all these dissimilar materials is a general process that raises the recurring question of whether Class 3 products may be reworked. Does IPC-J- STD-001 explicitly permit rework provided that the assembly is restored to full compliance with appli- cable requirements? 2 Yes, rework is allowed, but the defect must be dispositioned and documented as not meeting the requirements of the contract and/ or the specification. For Class 3 products, the repair process must be defined, documented, and approved by the regulating agency, and the acceptable condi- tions must be approved by the customer. The IPC standards recognize that manufacturing defects can occur and provide mechanisms for restoring compli- ance without compromising reliability. These provisions demonstrate that reliability depends on process control and verification rather than an absolute prohibition of corrective actions. Solder Joint: Metallurgical Evaluation of the Solder Joints Microsection analysis remains one of the most valu- able tools for evaluating soldering process quality, whether for process qualification or continuous monitoring of either raw boards or the final process. The testing would consist of assessment of solder wetting, verification of plated through-hole fill, eval- uation of intermetallic layer formation, or, on raw boards, the detection of voids and barrel cracks. Optical microscopy at magnifications between 200x and 300x is sufficient for evaluating solder joint quality. More detailed metallurgical inves- tigations may require scanning electron micros- copy (SEM). Microsection analysis provides direct evidence of process performance and is particu- larly valuable when confirming soldering profiles or investigating field failures. Flux Flux is used to prepare surfaces for soldering. It is acidic in nature, and its function is to remove the metallic oxides present on the metallic surfaces to be soldered. This is why the discussion of the various alloys was pertinent for highlighting the unique variability of different metals that will be soldered in a single process. Fluxes must be quali- fied for the soldering process to determine their impact on the materials being soldered, as well as on the laminate and solder mask materials previously applied to the raw boards. IPC-J-STD-004 is used to develop the qualification program for selecting the proper flux material. Proper flux penetration