Biased HAST Testing: Humidity Bias Reliability for PCBAs Biased HAST puts a powered assembly into a saturated steam environment and holds it there, typically at 130 C and 85 percent relative humidity, until an insulation failure appears or the test is complete. It compresses months of damp heat exposure into…

Pad Lift in PCB Assembly: Causes, Tests and Prevention Pad lift is the separation of a copper pad from the laminate beneath it, leaving the pad attached only by the plating of its via or by nothing at all. It appears after reflow, after wave soldering or after a repair,…

Plating Bath Specific Gravity: 4 Limits of the Hydrometer Plating bath specific gravity is the density of the working solution compared with the density of water, and it is the fastest chemical check available on the line. A sample is drawn, a hydrometer floats in it, and the reading tells…

Immersion Gold Bath: 4 Checks for a Reliable ENIG Finish The immersion gold bath is the last wet stage of an ENIG finish, and it works by displacement rather than by reduction. Gold ions in solution take electrons from the nickel beneath them, so the gold deposits as the nickel…

Drill Wander Control in Deep PCB Holes Drill wander is the lateral deflection of a drilled hole from the position and axis the program intended. On a 0.3 mm hole drilled through a 2.4 mm panel, a wander of 60 um at the exit is common unless the process is…

Plating Current Density: 4 Checks for Even Copper Plating current density is the current divided by the area being plated, and it is the single number that decides how fast copper builds on the panel. Too little and the deposit is thin and dull; too much and the copper burns…

Blowhole Defects in Wave Soldering: Causes and Cures A blowhole is a void that has pushed a bubble of gas up through the solder fillet and left an opening at the surface of the joint. It is not the same defect as a pin hole caused by shrinkage, and it…

Solder Mask Developing: 4 Causes of an Uneven Pattern Solder mask developing is the step that turns an exposed and cured coating into a finished pattern. The developer dissolves the unexposed coating that the artwork left on the pads, and it has to do so completely without attacking the mask…

Damp Heat: 6 Rules for Coated Assemblies A damp heat test holds an assembly at a controlled temperature and humidity for a defined period, usually under electrical bias, and then measures whether the insulation between conductors has survived the exposure. It is a slow test by design, because the mechanisms…

Stencil Aperture Misalignment: Finding Print Drift Fast Stencil aperture misalignment is a lateral offset between the aperture in the stencil and the pad on the board at the moment the squeegee passes. Typical limits sit near 25 um for fine pitch work, and the defect only becomes visible when the…