Backdrilling And Stub Removal In High Speed Boards A plated through hole that only needs to connect the outer layers still passes through the whole board, and the unused portion below the last connected layer is called a stub. At high frequencies the stub behaves as a resonant transmission line…

Ionic Contamination: Preparation, Placement and Process Control Ionic contamination is the residue of the soldering process that remains on the board in the form of dissolved salts and flux activators. It is conductive once it absorbs moisture, and it is the raw material for leakage currents and for electrochemical migration…

Surface Insulation Resistance Test On Assemblies Surface insulation resistance is a measure of how well a surface resists the flow of leakage current between two conductors. On an assembled board it is affected by the flux residue left behind, by the cleanliness of the process and by the humidity of…

Solder Paste Inspection Guide Solder paste inspection measures the deposit on every pad before a component is placed. It measures a process that has no other in line check, and it does so at the point where a correction is still cheap, which is why the data is more valuable…

Stencil Cleaning Methods Compared A stencil collects paste on both faces during a print run. The underside picks up paste that is squeezed under the foil and the apertures collect paste on their walls, and both of them change the deposit. Stencil cleaning is therefore a continuous process rather than…

SMT Adhesive Dispensing and Cure for Wave Soldering Adhesive holds surface mount components in place while the board passes over a wave of molten solder, and it does the job only if the dots are the right size, in the right place and cured to the right degree. A dot…

Conductive Anodic Filament Growth In PCB Laminate Conductive anodic filament, usually shortened to CAF, is a failure in which a conductive path grows through the laminate between two conductors held at different potentials. The path follows the interface between the resin and the glass fibre bundle, and once it bridges…

Moisture Absorption: Design Rules and Process Limits Every organic laminate absorbs a small amount of water from the air. The amount is measured as a percentage by weight and it looks trivial, yet the absorbed water changes the electrical and mechanical properties of the material and creates the internal pressure…

Unit Serialization and Traceability in PCB Assembly Traceability is the ability to answer a question about a board months after it was built: which laminate, which paste batch, which machine, which oven profile, which operator. It is required by customers in several industries and it is useful to everyone, because…

Component Baking Guide for Assembly Plastic packaged components absorb moisture from the air. When they are heated to reflow temperature the water turns to steam, and the pressure inside the package can crack the body, delaminate the die attach or lift the wire bonds. Component baking is the step that…