In-Circuit Test and Flying Probe Compared What Structural Test Does Structural test checks the assembly itself rather than the function of the product. It confirms that the components are present, of the right value and in the right place, and that the connections between them are intact. Because it does…

Functional Test Strategy for Assemblies What Functional Test Is For A functional test powers the assembly and exercises it as the product will be used, checking that the functions work together rather than that each component is present. It is the test that catches the defects that a structural test…

Box Build Assembly and Final Integration Where Box Build Begins Box build is the work that turns a finished board into a finished product: the enclosure, the harness, the connectors, the display, the fasteners and the label. It begins where board level assembly ends and it is where the last…

Rework and Repair of PCB Assemblies Rework or Repair The two words describe different things. Rework is the correction of a board that does not meet specification, restoring it to the intended design, such as replacing a component placed in the wrong orientation. Repair is the restoration of a damaged…

Solder Mask Defects and Their Causes What the Mask Has to Do The solder mask is the polymer layer that covers the board except at the pads, and it performs three jobs: it prevents solder from bridging between adjacent features during assembly, it protects the conductor from contamination and handling…

Copper Thickness and Current Capacity What Copper Thickness Means Copper thickness is quoted in ounces per square foot, where one ounce refers to a layer of copper weighing one ounce spread over a square foot, which corresponds to a thickness of roughly 35 micrometres. Standard boards use half an ounce…

Underfill and Edge Bonding for Assemblies Why Joints Need Reinforcement A solder joint is the mechanical as well as the electrical connection, and on a large area array package it carries a load that a small ball was never designed to take alone. Thermal cycling makes the package and the…

Stencil Design for Paste Printing The Stencil Sets the Volume Paste printing is a volumetric process, and the stencil is the tool that defines the volume. For a rectangular aperture the deposit is the area of the aperture multiplied by the foil thickness, so the design of the aperture and…

Wave and Selective Soldering Where Wave Soldering Still Fits Wave soldering remains the efficient way to solder through hole components at volume. A board passes over a standing wave of molten solder, and every joint on the underside is made in one pass, which is far faster than touching each…

Reflow Profile Development and Control What a Profile Is A reflow profile is the temperature of the assembly as a function of time, and the oven’s settings are only a means of producing it. The distinction matters because two boards in the same oven can see different temperatures, depending on…