Laser trimming-Custom Design Circuit Board
From Wikipedia, the free encyclopedia
Laser trimming is the manufacturing process of using a laser to adjust the operating parameters of an electronic circuit.
Laser-trimmed precision thin-film resistor network from Fluke, used in the Keithley DMM7510 multimeter. Ceramic backed with glass hermetic seal cover. Laser trim marks are visible in the grey resistive material
One of the most common applications uses a laser to burn away small portions of resistors, raising their resistance value. The burning operation can be conducted while the circuit is being tested by automatic test equipment, leading to optimum final values for the resistor(s) in the circuit.
The resistance value of a film resistor is defined by its geometric dimensions (length, width, height) and the resistor material. A lateral cut in the resistor material by the laser narrows or lengthens the current flow path and increases the resistance value. The same effect is obtained whether the laser changes a thick-film or a thin-film resistor on a ceramic substrate or an SMD-resistor on a SMD circuit. The SMD-resistor is produced with the same technology and may be laser trimmed as well.
Trimmable chip capacitors are built up as multilayer plate capacitors. Vaporizing the top layer with a laser decreases the capacitance by reducing the area of the top electrode.
Passive trim is the adjustment of a resistor to a given value. If the trimming adjusts the whole circuit output such as output voltage, frequency, or switching threshold, this is called active trim. During the trim process, the corresponding parameter is measured continuously and compared to the programmed nominal value. The laser stops automatically when the value reaches the nominal value.