Wave Solder Defects and Process Control Wave soldering is a process with a small number of variables and a large number of defect modes, and most of the defects are related to the interaction between the flux, the preheat and the wave rather than to the solder itself. The process…

Reflow Profile Control for PCB Assembly A reflow profile is the temperature that the board experiences over time, and it is the single most important variable in the soldering process. The same oven, paste and board can produce good joints or a range of defects depending on the profile, and…

Copper Weight Selection For PCB Layers Copper weight is the thickness of the copper foil on a layer, expressed in ounces per square foot. One ounce corresponds to about thirty five micrometres, and a standard board starts at half an ounce on the inner layers and one ounce on the…

Solder Paste Printing Defects and Control Solder paste printing is the step that decides the outcome of the whole assembly process, because a deposit that is wrong cannot be corrected later. Too little paste produces an open joint, too much produces bridging, and a deposit that is the right volume…

Stencil Cleaning Guide for PCB Assembly Stencil cleaning is a routine task that decides a large part of print quality, and it is often performed to a rhythm rather than to a standard. Paste residue left on the underside of a stencil smears onto the board and produces bridging, while…

Drill Program Optimisation And Hit Sequencing A drill program is the file that tells the machine where to drill, with which tool, at what depth and in what order. The first three are fixed by the board design; the order is the part that can be optimised, and it affects…

Nitrogen Purity in Reflow Soldering: Oxygen Levels and Cost Nitrogen is used in reflow ovens for one reason: it displaces oxygen, and oxygen attacks both the solder and the surfaces it has to wet. Removing it widens the process window, improves the appearance of the joint and reduces the amount…

Placement Nozzle Types and Selection for SMT Lines A placement nozzle is the only part of a pick and place machine that touches the component, and it is usually the cheapest item in the chain. That combination explains why it is so often the cause of a problem that is…

Solder Paste Jetting For Small Volumes Solder paste jetting deposits paste by ejecting a small droplet from a nozzle rather than by pushing it through a stencil aperture. It removes the stencil from the process entirely, which makes it possible to print a board that is not flat, to add…

Board Level EMI Filtering Guide Board level emi filtering is the practice of stopping unwanted energy at the point where it would otherwise leave or enter the board. Filters work by providing a low impedance path for the unwanted frequency while presenting a high impedance to the signal, and their…