Cleaning Equipment and Chemistry Selection Cleaning equipment is chosen from the residue that has to be removed and from the geometry that has to be reached, and not from a general preference for one technology. Aqueous, semi aqueous and solvent systems each suit a different combination of flux and assembly.…

Thermal Fatigue: Solder Joint Fatigue Under Thermal Cycling A solder joint fails under thermal cycling because the board and the component expand by different amounts and the joint has to absorb the difference. The damage accumulates with every cycle until a crack forms and propagates. Why Expansion Mismatch Drives It…

Laser Cut Stencil Aperture Quality and Sidewall Control A stencil is the tool that decides how much solder paste reaches every pad on the board, and a laser cut stencil is made by removing metal rather than by adding it. The cutting process leaves a sidewall with a defined angle…

Strain Gauge: Panel Strain Measurement During Depaneling Depaneling bends the board, and the bend is what breaks ceramic components. The damage is usually a microcrack that passes the functional test and fails after a number of thermal cycles, which is why the bending is measured rather than judged. Where the…

Tombstoning Causes and Process Cures Tombstoning is a chip component that has stood up on one end during reflow, and it happens because the two joints did not melt at the same time or did not apply the same force. The part is lifted by the surface tension of the…

Solder Wicking and Heat Robbing Control Solder wicking is the alloy travelling away from the joint into a region it should not reach, most often up a lead, along a pad or into a via. The result is a joint that is starved of the material that was intended for…

Flux Application Methods Compared Flux can be applied by spraying, by foaming, by dipping or by transferring a measured dot, and each method produces a different film on the board. The film thickness and the coverage decide whether the joint wets and how much residue is left behind. The method…

PCB Surface Finish Thickness Measurement and Control A surface finish does its job within a thickness range, and both ends of that range cause problems. Too thin and the finish is consumed before the joint forms; too thick and the joint becomes brittle or the finish stops behaving as designed.…

From Prototype to Production: Release and Change Control A prototype proves that the design works. Production proves that it can be made the same way every time, and the two are established by different evidence. The release is the point at which the evidence changes. What Has to Be Frozen…

Moisture Content Measurement in PCB Laminate Materials Laminate absorbs water from the air, and the amount it holds changes everything that happens to the board in a hot process. A panel that has been stored in a humid room will outgas in the press, the drill or the reflow oven,…