PCB Panelization, Tabs And Depanelization A single small circuit board cannot be handled economically. It cannot be printed, placed, reflowed or tested on its own without a fixture for every operation, so several boards are assembled into one panel with a frame and a set of rails around them. Panelization…

Solder Mask Dam Design Guide A solder mask dam is the strip of mask that runs between two adjacent pads. It looks like a leftover of the mask artwork, and it is one of the features that decides whether a fine pitch component can be assembled at all. A dam…

Loss Tangent and Insertion Loss in High Speed Laminates At low frequencies a trace behaves like a resistor. At multi gigabit rates it behaves like a transmission line, and the energy that does not reach the receiver has been absorbed by the conductor and by the dielectric. Loss tangent describes…

Conformal Coating Application Defects and Cures A conformal coating fails for the same reasons a paint fails: the surface was not clean, the film was applied too thin or too thick, or the environment during cure was wrong. The coating then protects nothing, and the failure appears as corrosion under…

PCB Fiducial Design Guide A pcb fiducial is a small mark on the board that exists purely so that a camera can find it. The placement machine measures the mark, compares its position with the programmed position, and shifts the whole placement program to match. Without the mark, the machine…

Moisture Sensitivity Level Management In Assembly Plastic packages absorb water from the air. Once that water is inside the moulding compound and the reflow oven brings the whole package above the boiling point of water in a few seconds, the vapour has nowhere to go and the package can crack…

Test Point Design Guide A test point is a piece of copper that exists only so that a machine or a person can touch the circuit. It takes no part in the function of the product, it costs area on every layer it passes through, and it is the difference…

Crosstalk Measurement and Eye Diagram Testing Methods Two traces running side by side are coupled, whether the designer intended it or not. Energy from one appears on the other, and at high data rates that coupling closes the eye, adds jitter and eventually causes errors. Crosstalk and eye diagram measurements…

Popcorning during Reflow: Causes and Prevention A board that looks perfect after reflow can still be internally damaged. Trapped moisture turns to steam during the thermal excursion, and the resulting pressure separates layers or cracks a plastic package from the inside. Popcorning during reflow is one of the few defects…

Development Board Layout for Application Processor Modules A development board exists to make a processor usable before the final product exists. It must expose interfaces, tolerate mistakes and stay flexible enough to support experiments that were not planned when it was designed. That brief is different from a production board,…