Hand Soldering Tip Selection and Care The soldering tip is the heat source, and most hand soldering problems that are attributed to technique are actually problems of heat transfer. A tip that is too small, too worn or too heavily oxidised cannot deliver enough energy to the joint, and the…

Sizing Thermal Via Arrays Under High Power LED Pads An LED converts only part of its input into light, and the rest becomes heat that has to leave through the board. Thermal vias are the standard way to move that heat from the pad under the die to a copper…

Solder Paste Expiry and Mixing Solder paste is a chemically active material with a shelf life, a thawing requirement and a working life in the printer, and treating it as a consumable that is either in date or out of date misses most of what affects the print. Two jars…

Destructive Failure Analysis Methods for PCB Assemblies Some failures cannot be seen from the outside. A cracked joint under a ball grid array, a delaminated interface, a void at the die attach and a crater in the laminate all require the assembly to be opened before the cause can be…

Reflow Conveyor Support, Sag and Vibration A reflow oven carries the board through the zones on a conveyor, and the board is supported only at its edges or not at all. At reflow temperature the laminate is softer than it is at room temperature, and what happens to the board…

Solder Wick Selection and Technique for Board Rework Solder wick looks like the simplest tool in the rework kit and behaves like one of the most demanding. Used well it removes a joint cleanly in a second or two with no damage to the pad. Used badly it lifts a…

Thermal Shock Test Methods for Assemblies Thermal shock testing moves an assembly between two temperature extremes as quickly as the equipment allows. It is not the same test as thermal cycling, even though both use temperature, and the difference determines which one is appropriate for a given question. Thermal shock…

Solder Mask Thickness and Its Measurement Solder mask is applied to a specified thickness, and the thickness decides the dam height, the electrical isolation and the cure. Measuring it is a routine check that is often replaced by a visual judgement, which is the point at which the specification stops…

Solder Ball Attach Defects and Their Causes A ball attach process places spheres on the package substrate and reflows them, and the defects it produces are mostly hidden until the package is assembled onto a board. The process window is narrow because the sphere has to form a joint and…

Orientation: Design Rules and Process Limits A polarized component that is placed the wrong way round produces a board that fails at test and, on some components, a board that fails immediately. The controls that prevent it are a mixture of the design, the data and the inspection, and they…