Bare Board Test: Preparation, Placement and Process Control A bare board is tested before any component is placed on it, and the purpose is to catch the faults that fabrication can produce: a broken trace, a short between two nets, a missing connection to an inner layer. Finding them at…

Rework Station Practice and Hot Air Profiling Rework is the correction of a defect after the board has been assembled, and it is the least controlled process on most lines. The equipment is simple, the decisions are made by an operator in a hurry, and the result is a board…

Precision Current Source Circuit Design A current source delivers a defined current whatever the load does, within a range of output voltages. It is the natural way to drive a resistance sensor, a laser diode or an LED, and the accuracy of the current is what the whole measurement depends…

Corrosion Inhibitors and Protective Films for PCB Surfaces Copper and silver both react with the air around them, and the reaction does not stop because the board is finished. A clean copper surface will oxidise within hours in a warm workshop, and an unprotected silver surface will tarnish in an…

Placement Accuracy: Design Rules and Process Limits A placement machine is judged by where it puts the components. The specification that a machine manufacturer quotes is measured under ideal conditions on a glass plate, and the accuracy that a product experiences depends on the board, the fiducials, the component and…

Precision Voltage Reference Design Guide Every measurement is a comparison with a reference, and in an electronic instrument that reference is a voltage. Its accuracy, its drift and its noise set the limit for the whole channel, and no amount of care in the following stages can recover what the…

Changeover: Preparation, Placement and Process Control A surface mount line produces a mixture of products, and every change from one to the next is an opportunity for an error. The stencil, the feeders, the program and the profile all have to change together, and a single item left behind produces…

Surface Mount Adhesive for Double Sided Assembly Adhesive is used on a double sided assembly to hold the bottom side components during the second reflow and through the wave. It is a small dot with a large influence on whether the parts stay in place. Why Adhesive Is Used A…

PCB Panel Size, Utilization And Cost Drivers A printed circuit board is not manufactured as an individual part. It is manufactured as a panel that carries several boards, or several hundred small ones, and the price of a board is the price of its share of that panel. Two designs…

Feeder Setup, Tape and Reel Verification The feeder is where the component enters the process, and its setup decides whether the placement program sees the part where it expects it. Most “placement” defects are feeder defects. What the Feeder Does The feeder advances the tape by one pocket each time…