LED Matrix Driver and Multiplexing Design An LED matrix replaces a wire per pixel with a grid of rows and columns, which reduces the number of connections from hundreds to a handful. The saving comes at a price: each LED is only lit for a fraction of the time, so…

Return Path Continuity and Reference Plane Splits A signal leaves its driver and returns to its receiver through a conductor that the schematic does not show. Where that return path is not continuous, the signal finds another route, and the change in the loop area is what produces the emissions,…

Stack-up Planning: Layers, Dielectric Thickness and Cost The stack-up is the decision that determines the impedance, the routing capacity, the cost and the fabrication yield of a board. It is usually made early, often by default, and revisited only when something has gone wrong. What the Stack-up Determines The number…

Solder Preforms and Step Soldering for Thermal Budgets Solder preforms are pieces of solder formed into a defined shape and volume, used where the joint needs more material than a paste deposit can provide or where the alloy has to melt at a temperature the rest of the assembly cannot…

Solder Preforms: Filling Joints That Paste Cannot Some joints cannot receive enough solder from paste. The hole is too large, the board is too thick, the component cannot tolerate the reflow temperature, or the joint is being repaired rather than produced. A solder preform is the answer. What a Preform…

Barrel Cracks in Plated Holes: Causes and Detection A barrel crack is a fracture in the copper that lines a plated through hole, running around the barrel or along its length, and it is the most common way a plated hole fails. The crack may be present when the board…

Board Level EMI Filtering at Connectors and Cables Most emissions and most immunity failures enter or leave a product through its cables. Filtering at the connector is therefore the highest leverage place to act, and it is also the place where a poorly designed filter does nothing at all. Why…

Current Transformer Interface Design Guide A current transformer measures alternating current by producing a smaller current in proportion to the one flowing in a primary conductor. It provides isolation for free, needs no supply of its own and works from the very low currents of a standby load up to…

LED PCB Assembly Process Step by Step A lamp board is simple in principle and unforgiving in production. Polarity, solder volume, cleanliness and a controlled ageing step decide whether the finished assembly survives its first hundred hours, and each of those controls is easy to skip under schedule pressure. Polarity…

BGA Solder Joint Repair: Options and Limits A ball grid array hides its solder joints underneath the package, so a joint that is marginal at assembly can survive test and fail in the field. Repair is possible, but the decision to repair depends on what the failure actually is and…