In the electronics industry, when the terms “High Quality and High Reliability” (“High-Rel”) are applied to the soldering of components, a level of conformance is required that is suitable for the product’s design as it relates to it’s operational environment.
Over time, the Department of Defense, NASA, other government agencies, as well as some commercial companies where component or solder joint failure is not an option, have established standards (such as MIL-STD-2000A “Standard Requirements for Soldered Electrical and Electronic Assemblies”). These standards, when utilized in the manufacturing process, yield products with a high level of quality, a very low failure rate over time, high margins of safety, and low levels of risk.
There are certain key elements that are intrinsic to achieving the high level of quality necessary to meet the specifications and standards of a “High-Rel” Assembly. The metrics used to assess the acceptability of a class 3 and a class 1 assembly, differ in their requirements, with a more stringent set of specifications applied to meet IPC class 3 requirements. In the same vein, the “High–Rel” assembly would undergo a more rigorous set of standards, which would exceed the more conventional requirements as outlined by the IPC J-STD-001.
Some of the key areas that help define the differences between the “High-Rel” environment and the more conventional IPC specifications are as follows:
- Soldering Tool controls - The Mil Specs have particular requirements for temperature, voltage, and current controls of the soldering equipment used for “High-Rel” assemblies. The IPC-J-STD-001 recommends guidelines in their appendix “B” for the isolation and temperature controls of soldering equipment, but does not specify requirements as does the MIL STD ( 45743, WS 6536, Mil STD 2000). A transient voltage of greater than 2V is not permitted under the Mil Spec guide, as an example.
- Visual Inspection - Good workmanship and knowledge of the standards for high reliability assemblies, and certain visual acuity requirements are needed to meet the “High-Rel” Mil standard assembly and inspection qualifications. The J-STD-001 has no such requirements. Additionally, the level of illumination required for inspection of a “High-Rel” assembly requires 1000 foot candle / sqft of lighting. In the IPC spec, this is only a recommended value.
- Component Damage - The “High-Rel” Standard will have limits to component damage and will specify the amount of allowable degradation. While the IPC–J-STD-001 refers to a degradation level below the part specification, the part specification is not always readily available to the inspection personnel.
- Definition of proper Solder Wetting – Proper wetting of the solder joint is extremely important to the reliability and integrity of the connection. The “High-Rel” standard of desired wetting will call for angles of no less than 20 degrees and no greater than 60 degrees. The IPC J-STD-001D calls for wetting angles of less than 90 degrees, with certain exception allowing angles of greater than 90 degrees.
- Improving Stress Relief – After the solder process, the requirements for the bend radii of component leads varies greatly between the “High-Rel” standard and the IPC standard. The IPC J –STD-001 allows solder in the bend radii as long as the solder does not touch the component body. The “High-Rel” standard only allows it on the inside bend of the component. This condition allows for better stress relief. The application of solder by hand soldering, wave soldering, or reflow soldering using solder paste, is done in such a manner as to obtain a concave solder fillet with a very low wetting angle. The lead, wire, terminal, or contact should be readily distinguishable in the solder. Solder coverage as to wire type, size and specific attachment as well as specific component type and lead/contact configurations, are described in the specification. There is also specific solder coverage issues related to the environment (salt or corrosive atmosphere), high voltage, or high frequency.
- Wire Insulation Removal, (Stripping) - Use only tools and methods which impart NO DAMAGE or deformation to the insulation to the wire or wire strands. The IPC J-STD-001D for class 3 allows damage and severed strands for wires exceeding 7 strands. The “High-Rel” standard would not allow for “birdcages” or damage of any form that exceeds 5% of the wire diameter.
- Wire/Component Lead Preparation (Tinning) - Tin stranded wires, in such a manner, as to assure solder penetration to the inner strands to obtain proper wetting without excessive solder on the exterior strands. This activity will enhance wetting and prevent strand separation during formation and attachment to terminals.
- Wire/Component Lead Forming and Attachment - Form wires and leads for attachment to terminals in order to attain ideal mechanical contact, preventing movement during the soldering process. Also form and dress wires and leads in such a manner as to provide maximum stress relief. There are other considerations for both wires and component leads specific to size, type and specific attachment described in the specifications. The IPC J-STD-001 allows for misalignment for class 3 of 25% of the component / lead width. The “High-Rel” Standard does not allow for any side or toe overhang. Any solder build-up can only exist as thin film.
- Plated Through Hole Configuration - Plated through hole (PTH) component leads should be formed in such a manner that the component bodies are approximately centered within their hole span, and surface mount (SMT) devices approximately centered on their designated land patterns. Again, specific component types/lead forms have mounting requirements defined in the specification. The IPC J-STD-001 requires a 75% hole fill and a 25% depression, but does not require wetting to the land pattern on the primary side of the PWA. The “High-Rel” standard would require a wetted primary surface to re-enforce the plated hole bond.
- Cleanliness Requirements - All soldered connections should be properly cleaned (and not damaged or further contaminated in the cleaning process), and be free of any surface contaminants or particulate matter, including solder balls of any size or shape.
While there are many other considerations as to “High Quality, High Reliability Soldering”, required to meet “High-Rel” standards, proper materials, process definition, process control and continuous process improvement, are the primary goals of this standard to increase quality, improve first pass yield, and reduce costs.
In order to meet the needs of customers, agencies, and special clients for High Quality – High Reliability Soldering Training, the EMPF can provide custom “High-Rel” Soldering Technology Training. In addition to the current IPC J-STD-001 Training/Certification program, specific custom courses can be developed to meet the training requirements needed to equip employees with the necessary skills to produce “High-Rel” products
For additional information please contact the Training Center Registrar via email: email@example.com, phone: 610-362-1320, or sign up on the web site at http://www.aciusa.org.