Invented in the 1930s, the printed circuit board continues to improve and evolve. Most soldering is now completely automated, speeding assembly and reducing costs. Lead and other hazardous materials are being phased out in favor of safer alternatives.
Automated
In mass production, a solder paste is applied to the circuit board. A mask blocks off areas where the solder won't go. Parts are placed on the top side of the circuit board, and it goes into an oven. The solder melts, fixing the parts to the board.
Manual
Small production and prototype circuit boards are handmade. They're soldered one connection at a time with a soldering iron. Today's smaller parts call for a steady hand and careful technique.
Resoldering
Circuit board materials can handle only a limited amount of desoldering and resoldering. The glue that holds the copper foil may break down, causing the foil to peel. If the board material overheats, it will weaken.
SMD
To keep costs down and to automate manufacturing, most parts are now surface-mount devices. They're smaller than their predecessors and have short, flat pins flush with the bottom of the part. They solder directly to the top of the circuit board.
ROHS
In keeping with the European Union's Reduction of Hazardous Substances Act, more circuit boards are made with lead-free solders. The newer solders are formulated with silver, copper, bismuth and other metals in place of lead.
