Solder Paste Storage, Expiry and Handling Why Solder Paste Is Perishable Solder paste is a suspension of fine alloy powder in a flux vehicle, and that mixture changes from the moment it is made. The flux slowly reacts with the powder, the solvent evaporates, and the rheology drifts. A paste…

BGA Rework and Rework Profiles Why BGA Rework Is Different Reworking a ball grid array means heating an entire package through the board until every joint in the array is liquid at the same time, then removing or replacing the package without disturbing the neighbours. Unlike a gull-wing part, the…

Design for Test on PCB Layouts What Design for Test Means Design for test is the practice of making a board easy to verify while it is still being laid out. It covers test point access, the placement of alignment features, the routing that lets a tester isolate a node,…

In-Circuit Test and Nail Bed Fixtures What In-Circuit Test Does In-circuit test measures each component and each net on a populated board while the board is still in its assembly state. The tester contacts every node through a fixture and applies signals and measurements that isolate one component at a…

Flying Probe Testing for Prototypes How Flying Probe Testing Works A flying probe tester uses a small number of moving heads that travel to each test point in turn, contact the pad with a fine needle, and measure the electrical property being checked. Instead of a fixture with thousands of…

Panelization Choices for Assembly Why Panels Exist Placement machines, printers, and reflow conveyors are built around a panel size, not a single board. Panelization combines several boards into one array that fits the machine, is stiff enough to travel without flexing, and can be handled by the loader without damaging…

V Scoring and Board Separation What V Scoring Is V scoring cuts a shallow groove along both faces of a panel so that the individual boards can be snapped apart after assembly. The two opposing grooves leave a thin web of laminate in the middle that holds the panel together…

Controlled Impedance Testing and Verification Why Impedance Has to Be Verified Controlled impedance is a promise made by the stackup and kept or broken by the fabrication process. The design assumes a specific trace width, dielectric thickness, and dielectric constant for each signal layer, and the fabricator hits those targets…

Voids and Bubbles in Conformal Coating What Coating Voids Are A void is a gap in a conformal coating where the film does not cover the surface, or where an air pocket is trapped within or beneath the film. Bubbles are the visible form: a raised blister in the coating,…

Underfill for Area Array Packages What Underfill Does Underfill is a filled epoxy that is dispensed along the edge of a mounted package and flows by capillary action into the gap between the package and the board, filling the space around every solder joint. Once cured, it mechanically couples the…