Potting: Design Rules and Process Limits Potting surrounds an assembly with a material that cures into a solid or a gel, and it does three jobs at once: it excludes moisture and contamination, it supports the components mechanically, and in some designs it carries heat away. Encapsulation is the same…

Laminate Selection: Glass Transition Temperature And Loss The laminate under the copper determines how the board behaves when it is heated, how fast a signal travels along a trace, how much of that signal is lost on the way, and how well a plated hole survives a lead free reflow.…

PWM Driver Circuit Design for Solenoids A solenoid draws a large current to pull its armature in and needs much less to hold it there. A PWM driver exploits that difference: it applies the full supply for the pull in and then switches rapidly to hold the current at a…

BGA Rework: Removal, Site Preparation and Reballing A ball grid array cannot be soldered twice the way a leaded part can. The joints are underneath the package, the whole array has to reach the melting point at the same time, and the surrounding board has to stay cool enough that…

SMT Adhesive For Wave Soldering And Dispensing On a mixed technology assembly, the surface mount parts on the underside have to survive a wave of molten solder while the through hole joints on the top side are being made. A small chip component has nothing to hold it in place…

ESD Protection Layout Design Guide An electrostatic discharge is a current pulse of tens of amps with edges measured in hundreds of picoseconds. No device survives it by absorbing the energy; the circuit survives by giving the current a short path to ground that bypasses everything sensitive. What the Discharge…

Gap Filler Dispensing for High Power PCB Assemblies Many power assemblies have a gap between a component and its heat sink that is too wide or too uneven for a thin thermal interface material to bridge. A gap filler is a soft, heavily loaded polymer dispensed into that space, where…

Paste Jetting and Dispensing for Odd-Form Components A stencil prints a whole panel at once and does it well. It stops being the right tool when the board is not flat, when the paste has to go somewhere a squeegee cannot reach, or when the volume needed at one location…

Clean or No-Clean: Making the Residue Decision The choice between cleaning and leaving the flux residue is made on cost, and it should be made on the requirement. The two are not equivalent processes and the difference appears later. What No-Clean Means A no-clean flux is formulated so that the…

EMC Shields, Gaskets and Frame Grounding Where a board has to be shielded, the enclosure, the frame and the gasket form the shield. A gap in the path is the difference between an attenuation figure and a product that fails the radiated emission test. What the Shield Has to Do…