Solder Paste Powder Type and Particle Size Selection Solder paste is a suspension of alloy powder in a flux vehicle, and both halves of that description matter. The powder determines how the paste behaves in a small aperture and how it melts; the flux determines how it wets, how it…

Thermocouple: Thermal Measurement Point Selection and Accuracy Every thermal design rests on temperature measurements, and a measurement taken with the wrong attachment or the wrong instrument can be several degrees out. The error is usually in the direction that makes the design look safe. What Is Being Measured The quantity…

Isolation Transformer Design Guide An isolation transformer transfers energy through a magnetic field rather than through a conductor, so the two sides have no electrical connection. That single property is what makes it a safety component, a noise barrier and, in some designs, the whole reason the product can be…

Solder Joint Strength Testing: Shear and Pull A solder joint has to do two jobs: carry the current and hold the component in place. The second job is verified by a mechanical test, and the tests that are used in production and in qualification answer slightly different questions. The value…

Placement Accuracy Verification and Process Capability A placement machine reports an accuracy figure, and the figure describes the machine rather than the process. What matters on a product is where the parts actually land, and whether the distribution fits inside the pad. Accuracy and Repeatability Accuracy is how close the…

Board Warpage Control Through Reflow A board that leaves fabrication flat does not necessarily stay flat. The reflow process heats it above the glass transition temperature of the laminate, where the material becomes soft and the internal stresses that were built in during lamination are free to relax. The result…

PCB Solder Paste Traceability: What Matters on the Production Line Buyers and engineers often focus on the finished product and forget the production line behind it. In practice, most field failures can be traced back to process decisions made during assembly. Understanding PCB solder paste traceability gives you a practical…

Stencil Design: Area Ratio and Step Stencils The stencil is the tool that turns a design into a deposit, and it is the only part of the printing process that is made specifically for the product. Its thickness, its apertures and the way it is tensioned all determine how much…

X-ray Inspection of Area Array Solder Joints An area array package has its joints under the body, so the only practical way to look at them without destroying the assembly is with X-ray. The image shows a lot and it does not show everything. What the Image Shows A two…

Bend Test and Flex Testing Methods for Assembled Boards Bending is the most common way an assembled board is damaged, and it is also the least noticed. A board flexes when it is snapped out of a panel, pressed into a housing, clamped in a fixture or simply picked up…