Fabrication Capability Matrix and Its Use A fabrication capability matrix is a short table of the limits a shop can hold, and it exists so that a design can be checked against them before it is quoted. Without it, the check is made by whoever answers the enquiry on that…

Ionic Contamination Verification Ionic contamination is the residue that remains conductive when it dissolves in moisture, and it is the mechanism behind a whole family of failures: dendritic growth between conductors, leakage across a connector, corrosion of a joint and, in the worst case, a short that appears only in…

Component Bake Schedules and Floor Life A component that has absorbed moisture and is heated quickly can crack internally, and the crack is invisible from outside. The bake is the operation that removes the moisture before the heat arrives, and its schedule is set by the package rather than by…

Assembly DFM Review Agenda A manufacturability review is the last cheap opportunity to change a design. After the layout is released, a change costs a revision, a new stencil, a new program and possibly a scrapped panel; before release, it costs a conversation. The difference between a review that finds…

Solder Paste Open Time and Work Life on the Line Solder paste changes from the moment the jar is opened. The solvent evaporates, the flux chemistry reacts with the air and the viscosity rises, so a paste that printed correctly in the morning behaves differently in the afternoon. Open time…

Paste Kneading and Print Stability Over a Shift Solder paste is a suspension, and a suspension separates. Kneading is the operation that restores the mixed state before printing, and the stability of the print over a shift depends on it being done consistently rather than quickly. What Happens Without Kneading…

Moisture Sensitivity Level and Floor Life Control A plastic package absorbs moisture from the air. When it is heated to reflow temperature the moisture turns to steam, and the pressure can crack the package from the inside, delaminate the die attach or lift the wire bonds. The damage is called…

Visual Criteria for Solder Joint Acceptance A visual acceptance criterion is a sentence and a photograph, and the two have to agree. Where they do not, the criterion is interpreted differently by different inspectors, and the difference shows up as an inconsistent yield rather than as a defect. What the…

Impedance Test Method Verification An impedance test is a measurement, and a measurement has an uncertainty. Verifying the test means establishing what the instrument, the probe and the coupon contribute, so that a reading outside tolerance is a real excursion rather than a change in the measurement. What the Measurement…

Hand Soldering Tip Selection and Care The soldering tip is the heat source, and most hand soldering problems that are attributed to technique are actually problems of heat transfer. A tip that is too small, too worn or too heavily oxidised cannot deliver enough energy to the joint, and the…