Package on Package Design Guide Package on package places a memory device on top of a logic device and connects the two through a ring of solder joints around the edge of the lower package. The arrangement saves board area and shortens the connection between the processor and its memory,…

Stencil Cleaning Frequency For Solder Paste Printing Stencil cleaning is one of the least visible steps in surface mount printing and one of the most influential. Paste left inside the apertures and on the underside of the foil changes the volume transferred at every subsequent print. The change is gradual,…

Reflow Oven Zone Balance And Profile Control A reflow oven is a series of heated zones along a conveyor, each holding a set temperature with its own airflow. The board absorbs heat as it passes, so the zones do not act independently. They interact through the thermal mass of the…

Counterfeit Components: Preparation, Placement and Process Control Counterfeit components reach production through the same channels that supply legitimate parts, and they are most likely to appear when a device is scarce, when a part has gone obsolete, or when a price is offered that is well below the market. The…

Underfill Process Guide for PCB Assembly Underfill is a filled polymer that is dispensed beside a package and drawn under it by capillary action, where it locks the solder joints to the board and spreads the strain that thermal cycling would otherwise concentrate on the outermost balls. It is used…

Conformal Coating Defects and Prevention Conformal coating protects a board against moisture, contamination and ions that would otherwise promote corrosion and electrochemical migration. The coating only works if it is continuous and adherent, and most defects are not caused by the coating material itself but by the state of the…

Selective Soldering Process Control Selective soldering fills the gap between reflow and hand soldering. It is used where a board carries a small number of through hole parts that cannot survive a reflow oven, or where the thermal mass of a connector makes a wave impractical. The process is slower…

Reflow Cooling Rate Control: Why the Down Slope Matters The reflow profile is usually drawn with most of its detail on the way up: ramp rate, soak, peak and time above liquidus. The down slope gets whatever remains of the oven, and yet the way a joint cools decides much…

Drill Bit Geometry And Hole Quality A printed circuit board drill is a twist drill made of solid tungsten carbide, with a geometry that has been adapted for cutting a stack of resin and glass rather than metal. The point angle, the helix, the web thickness and the surface treatment…

ENEPIG Finish: Selection, Reliability and Solder Joints An electroless nickel electroless palladium immersion gold finish, usually shortened to ENEPIG, was introduced for a specific problem: a board that has to be soldered and also wire bonded. The older gold finishes served one of those duties well and the other badly,…