SMT Changeover and First Article Discipline A surface mount line produces a mixture of products, and every change from one to the next is an opportunity for an error. The stencil, the feeders, the program and the profile all have to change together, and a single item left behind produces…

Troubleshooting: Key Checks Before Release Troubleshooting a reflow defect is easy when the cause is obvious and slow when it is not. A structured sequence keeps the investigation from moving to the least likely cause first, which is usually where time is lost. Start With the Defect Class The class…

Wire Harness: Preparation, Placement and Process Control Where a wire harness meets a board, the electrical connection is only half of the problem. The harness is a mechanical object with mass, stiffness, and a routing path, and every movement of the product, every thermal cycle, and every pull on the…

Drop Test: Preparation, Placement and Process Control Dropping a product is one of the most severe mechanical events it can experience, and it happens in a fraction of a second. The acceleration involved can exceed a thousand times gravity, and the whole event is over before any protection circuit could…

Low Temperature Solder Alloys Compared With SAC305 A lead free assembly is normally soldered with an alloy of tin, silver, and copper that melts at about two hundred and seventeen degrees Celsius, which forces a peak reflow temperature above two hundred and forty. That temperature is close to the limit…

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…