Nitrogen in the Reflow Process What Nitrogen Changes in Reflow Nitrogen does not solder anything. It displaces oxygen so that the surfaces being joined stay metallic instead of oxidizing while they are hot. Reflow is a race between wetting and oxidation, and at the temperatures used for lead-free alloys the…

Solder Pallet Design for Selective Soldering What a Solder Pallet Does A solder pallet is a machined carrier that holds a printed circuit board during selective soldering, masking the areas that must not see solder while exposing the through-hole joints that must. It also provides mechanical support so the board…

Flux Residue and Its Effects on Assemblies What Flux Residue Is Made Of Flux is a chemical tool. It removes oxide from the copper and the solder, lowers surface tension so the molten alloy wets properly, and then has done its job. What remains after reflow or wave soldering is…

Pad Cratering Under Area Array Packages What Pad Cratering Actually Looks Like Pad cratering is a fracture that begins inside the laminate rather than at the solder joint. Instead of the joint or the pad separating cleanly, a crack opens in the resin below the copper pad and spreads outward…

Solder Balls and Spatter on Assemblies What the Defect Looks Like Solder balls are small spheres of metal sitting on the board surface, often near a joint, sometimes inside a mask opening and sometimes on top of the mask. Spatter is a related defect, in which small particles are ejected…

Preventive Maintenance of SMT Equipment Why Equipment Maintenance Is a Quality Activity Much of what looks like process drift is equipment wear. A printer’s squeegee rounds, a feeder’s sprocket wears, a nozzle’s tip flattens, an oven’s heater loses output, a conveyor’s speed drifts, and the defects that appear are attributed…

Mistake Proofing in Electronics Assembly The Principle Mistake proofing, or poka-yoke, makes an error impossible or immediately visible rather than relying on a procedure or an operator’s attention. The principle is that a person performing a repetitive task under time pressure will eventually make a mistake, and that the system…

First Pass Yield and How to Improve It What First Pass Yield Measures First pass yield is the proportion of units that pass all the tests the first time, without a rework or a retest. It differs from the final yield, which counts the units that pass after being reworked,…

Process Capability and Cpk on an SMT Line What Capability Measures Process capability compares the spread of a process’s output with the limits that the specification allows. A process whose output fits comfortably inside the limits is capable; one whose output spreads to the limits or beyond is not, however…

Failure Analysis of Field Returns Why Field Returns Matter A field return is the most informative object in a manufacturing organisation, because it is a real failure with a real history rather than a hypothesis about a process. Its value depends on the discipline applied to it: a return that…