Thermal Cycling Test Setup For PCB Reliability Thermal cycling is the standard accelerated test for solder joint and plated hole reliability. The assembly is taken repeatedly between two temperature extremes, and damage accumulates at the interfaces where materials with different expansion coefficients meet. The value of the test depends entirely…

Dross Reduction in Wave Soldering: Causes and Control Dross is the oxide and intermetallic skin that forms whenever molten solder meets air, and a wave solder pot produces it continuously. It consumes alloy, it has to be removed by hand, and the removal itself costs money and adds a small…

Nitrogen Reflow: Design Rules and Process Limits Nitrogen reflow soldering replaces the air in the oven with an atmosphere that contains very little oxygen. The immediate effect is that the metals being joined do not re oxidise during heating, so the flux has less work to do and the solder…

Vapor Phase: Design Rules and Process Limits Vapor phase soldering heats a board by immersing it in a saturated vapour whose temperature is fixed by the boiling point of the fluid. The vapour condenses on the board and releases its latent heat, which gives an extremely uniform transfer that does…

Solder Pot Contamination in Wave Soldering Machines A wave solder pot holds several hundred kilograms of molten alloy at around 250 degrees Celsius, and it is exposed to everything the process brings with it: copper from the boards, iron from the fixtures, flux residues, oxide and the plating of the…

Layer Count Selection For Multilayer Boards Layer count is the first structural decision in a multilayer design, and it drives almost everything that follows: the stackup, the board thickness, the impedance options, the via structure and the price. It is also one of the decisions most often made too early,…

Minimum Line Width Selection For PCB Designs The minimum line width on a board is the narrowest conductor the fabricator can produce reliably on that particular stack, and it is one of the first questions a designer should ask. A value that is too aggressive increases cost and reduces yield,…

Stencil Design Rules for SMT Printing A stencil is a thin metal foil with apertures cut to match the pads, and it is the tool that decides how much paste reaches each pad. The printing process has little room to correct a stencil that is wrong, so the stencil design…

Solder Paste Thawing: Design Rules and Process Limits Solder paste is a mixture of solder powder, flux and a solvent system, and its behaviour changes with temperature and with time. Most printing problems that are blamed on the printer or the stencil can be traced to paste that was used…

Gold Finger Plating For Edge Connectors Edge connectors are the part of a board that is inserted into a socket or a card cage, and they take more mechanical abuse than any other feature. The gold finger plating on those contacts has to survive repeated insertion, abrasion against the socket…