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December 18, 2025 - Updated December 3, 2025 - Originally Posted Process Controls When Running Multiple LinesWhat process controls are essential for ensuring consistency when multiple lines run the same assembly with slightly different equipment? U.L. |
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Recent SMTA test-board studies led by Chrys Shea have shown that ultra-miniature components can be printed far more reliably than many engineers expect, even with Type 4 solder paste. Her published technical articles highlight how print performance depends less on powder size alone and more on the interaction of stencil technology, aperture geometry, and process tuning. The SMTA Test Board, with its structured layout of 0201, 01005, and micro-pitch features, was specifically created to expose the limits of a printing process and to separate real capability issues from assumptions about paste type. Across multiple evaluations, Shea demonstrated that 01005 components fall well within the printability window of Type 4 paste when the stencil design is optimized. Improvements such as shifting from square apertures with rounded corners to fully circular apertures raise the effective area ratio and promote more consistent paste release. Likewise, nano-coated, fine-grain stencils significantly reduce adhesion on side walls, helping compensate for borderline AR conditions and improving transfer efficiency without relying on higher-cost Type 5 materials. The broader takeaway is that print quality at these dimensions is a process engineering challenge, not just a paste-selection problem. Type 4 solder paste remains fully capable for 01005 printing when paired with the right stencil choices and parameter controls. For teams looking to evaluate their suppliers, or justify decisions on stencil thickness, aperture design, or paste type, the SMTA Test Board from Shea Engineering offers a proven, data-driven way to validate real performance before investing in more expensive materials.
Marketing 360-Biz Douglass Dixon is the Chief Marketing Officer for 360 BC Group, a marketing agency with offices throughout the US. 360 BC specializes in consulting and implementing successful marketing programs that utilize the latest in marketing, sales and technology strategies. As an electronics veteran, Dixon has worked in the industry for over 30 years for companies like Henkel, Universal Instruments, Camelot Systems, and Raytheon. Dixon's electronics industry experience includes a broad skill set that includes engineering, field service, applications, product management and marketing communications expertise.
There are far too many processes, even in a simple PWA/PCB assembly “line,” to attempt to define all the “essential” process measurements for each in a single reply. One process that I will address here is the mass soldering process, whether reflow or wave or both in the same line. It is essential to ensure (and document) the thermal profile experienced by the PWA/PCB assembly during the mass soldering process. The thermal profile of the solder joints and components must remain below the component limits and within the solder (paste) tolerances. The essential measurements required for this process are well defined in the Global Electronics Association (AKA: IPC) document IPC-7530, “Guidelines for Temperature Profiling for Mass Soldering Processes (Reflow and Wave).” There are several thermal profiler recorders available, all of which can measure temperature over time and extract key process indicators (KPIs), enabling you to document these measurements across your lines with “slightly differing equipment.” Do not assume — even if your line uses the same model reflow or wave soldering machines, it cannot be assumed that the same recipe (machine settings) will produce the same thermal profile across each line. Documenting it by performing the actual thermal profile is the only way to know and prove consistency across you lines.
Senior Project Engineer Electronic Controls Design Inc Paul been with Electronic Controls Design Inc. (ECD) in Milwaukie, Oregon for over 39 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, engineer, manufacture, and customer. His focus has been the design and application of measurement tools used to improve manufacturing thermal processes and well as moisture sensitive component storage solutions.
Consistency between the lines is best achieved when you can make the printing process consistent. If you are lucky enough to have the same printers that are properly calibrated (snap-off, support, squeegee pressure) you’re most of the way there. If you have solder paste inspection you have a good point at which to optimize the print consistency, especially if the lines have different printing equipment. Differences in placement equipment shouldn’t be a big impact as long as it’s placing the parts on the pads. Different reflow equipment may take some time to generate the same profile on both ovens but it’s something that can be achieved. Start with the same belt speed and work with the temps and convection to get a similar profile on both ovens. The process window for modern solder pastes is pretty wide, but you want to focus on getting time above liquidus and pead temps in the same range.
PCBA Engineering Liaison General Atomics Electromagnetic Systems Group Kevin has over 30 years of experience in process and manufacturing engineering serving in both EMS and OEM companies. Expertise includes all aspects of SMT as well as wave solder and CCA materials such as PCBs, solder material, and component finishes. Kevin has developed processes for thousands of assemblies from stencil printing to conformal coating and testing.
In my experience working across different manufacturing and assembly environments, electronics, medical devices, plastics, metal-mechanic parts, the most important factor when multiple lines build the same assembly with different equipment is to minimize process variation, so the final result remains the same regardless of which line produced it. Machines can differ; the product cannot. That’s why all lines must follow the same defined parameters or at least the critical ones use equivalent methods, and apply aligned inspection criteria, controlling both process inputs (set-ups, materials, programs, thermal profiles) and process outputs (visual and functional quality). To achieve this, common process controls should be implemented, such as:
Methodologies such as IATF 16949, Lean Manufacturing, Six Sigma, Jidoka, Poka-Yoke, or even Industry 4.0 centralized monitoring are all valid frameworks depending on the industry. Each one provides a different structure, but all pursue the same goal: Reduce process variation and ensure the same product quality, no matter which line built it. When these controls are properly implemented and sustained, the manufacturing system becomes robust, stable, and fully comparable across equipment, achieving the fundamental objective: same process, same results, every time.
Engineering Director / Master IPC Trainer (MIT) AMMSA Solutions More than 20 years of technical experience in the electronics industry in roles ranging from Process & Project Engineer to engineering manager and Technical Applications Engineer for Latin Americas. IPC Master Trainer, International speaker and consultant.
What process controls are essential for ensuring consistency when multiple lines run the same assembly with slightly different equipment? PCBA:
Process Supervisor NexPCB Co; Ltd 25 years experience in SMT/COB industry, 10 years in Optical film by Sputtering and Evaporation.
When multiple lines build the same assembly, it helps to separate the discussion into materials and process. Materials: Even when processes are aligned, variability often enters from the components and PCBs themselves. A growing approach in the industry is using line-integrated visual integrity checks, essentially analyzing the high-resolution images already captured by AOI systems to confirm that each component’s markings, physical characteristics, and origin indicators remain consistent across all lines. This provides a uniform “material signature” for every board, regardless of which line built it. (If you search for terms like visual component integrity or board-level integrity assurance, you’ll find good examples of this emerging practice.) Process: On the process side, the essentials remain: keeping stencil revisions aligned, harmonizing SPI targets, maintaining placement and nozzle calibration, and ensuring reflow profiles are within a shared envelope. Many factories still see drift between lines, so the key is simply maintaining version control and regular cross-line comparisons. By combining visual integrity assurance for materials with solid but practical process controls, manufacturers can achieve consistent outputs even when equipment and setups vary slightly between lines.
CTO Cybord Electronic and Mechanical Engineer with 25 years experience in technology development. CTO of Cybord, developing electronic component authentication technology using deep-tech visual inspection and big-data. Author of a book and 24 papers.
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