What is the significance of laser trimming?

Laser trimming is a manufacturing process that uses a laser to adjust the operating parameters of an electronic circuit. laser trimming

Fluke’s precision laser trimming thin film resistors network used in Keithley’s DMM7510 multimeter. Ceramic back with sealed glass cover. Laser cropmarks appear on gray resistant material

One of the most common applications is to use a laser to burn off a small piece of a resistor to increase the resistance of the resistor. The combustion process can be carried out while the circuit is being tested by an automatic tester to obtain the optimum final value of resistance in the circuit.

The resistance value of a layered resistor is determined by its geometric dimensions (length, width, height) and the material of the resistor. Lateral cutting of resistant material with a laser narrows or lengthens the flow path of the current, increasing the resistance value.

The same effect can be achieved if the laser modifies the thick or thin film resistance on the ceramic substrate, or the SMD resistance on the SMD circuit. SMD resistors are made using the same technique and can also be laser trimmed.

Trimmable chip capacitors are configured as multi-layer plate capacitors. Evaporating the top layer with a laser reduces the area of ​​the top electrode and thus the capacitance.

Passive trimming is setting the resistance to a specific value. When trimming adjusts the performance of the entire circuit, such as output voltage, frequency, and switching thresholds, it is called active trimming. During the trimming process, the corresponding parameters are continuously measured and compared to the programmed target values.

When the value reaches the nominal value, the laser will stop automatically. One type of passive trimmer uses a pressure chamber to allow drag trimming in a single pass. The LTCC board contacts the test product on the component side and is trimmed with a laser beam on the resistor side.

This trimming method does not require a contact point between the resistors because the fine pitch adapter contacts the component on the opposite side where the trimming takes place. Therefore, the LTCC can be deployed more compactly and at low cost.

High speed laser trimmer with pressure chamber
Function mode:

The LTCC is mounted on the contact block. The rigid probe contacts the circuit from the other side. From the top, the chamber is pressurized from 1 to 4 bar and has a controlled exhaust port to provide air flow through the chamber. When the resistant material vaporizes, the particles of waste are removed in the air stream. Advantages of this method:

Trim an unlimited number of printed resistors in one step without being disturbed by the test probe. The board, adapter, or system is clean. Density up to 280 dots / cm².
Designers often use potentiometers that are tuned during final testing until the desired functionality of the circuit is achieved. In many applications, product end users do not want a potentiometer because it can cause the potentiometer to drift, be misaligned, or be noisy. Read more…

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