Surface Finish Thermal Aging A surface finish is not a passive coating. It is a thin layer of metal with its own diffusion behaviour, and it changes from the moment it is applied. Thermal aging is the process by which that change becomes a soldering problem, and it happens during…

Countersink and Counterbore Tolerance for PCB Machining Countersunk and counterbored holes look like simple machining details, and on a drawing they are often specified with a single note and no tolerance. In practice both features interact with screw geometry, panel thickness and plating, and a small error in either one…

Solder Mask Colour and Its Process Effect Solder mask is supplied in a range of colours, and the colour is a pigment rather than a property. The pigment changes the cure, the resolution and the inspection contrast, which is why a colour change is a process change. What the Colour…

Reflow Conveyor Vibration: Causes, Symptoms and Fixes Conveyor vibration is one of the few reflow faults that leaves no trace in the profile data. The thermocouples read correctly, the zones hold their setpoints, and the oven passes its daily check, yet boards come out with shifted chip components, tombstoned passives…

Copper Thickness Measurement Methods on PCB Copper thickness is specified for the current it carries and for the impedance it produces, and the figure that matters is the finished thickness rather than the foil that was purchased. Measuring it correctly means knowing which of the two is being reported. Foil…

Via Tenting: Key Checks Before Release A via that passes through a solderable area has to be dealt with. The two standard answers are tenting, where solder mask is printed over the hole, and plugging, where the hole is filled with a material before the mask is applied. The names…

Solder Mask Plugging Versus Tenting: Which Vias Need It Solder mask plugging and via tenting are often treated as interchangeable ways to keep solder out of a via, but they belong to different process families and leave different surfaces behind. Tenting is a mask-only operation in which the imaged film…

Stackup Dielectric Thickness A stackup is usually specified by the number of layers and by the finished board thickness, and both of those numbers can be met while the dielectric thicknesses inside the board are wrong. The inner layer spacing is what sets the impedance, the crosstalk and the coupling,…

Wicking: Preparation, Placement and Process Control Solder wicking is the movement of molten alloy along a metal surface under capillary action. In a barrel it is what fills the joint, and on a stranded wire or a pad it is what carries alloy where it was never meant to go.…

Washable Versus No Clean Flux Selection for Assembly Flux choice is often made at the same time as the solder alloy and then left alone for years, even though it decides whether the assembly needs a cleaning line, what the residue will do in service and how much process control…