Resistor Laser Trimming Thermoelectric Offset Compensation
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Solution Overview
Problem
Laser trimming of resistors is limited by thermoelectric potentials, which cause inaccuracies and are difficult to correct, especially in low-ohm resistors, leading to significant thermal voltage effects that distort resistance values and complicate high-accuracy trimming.
Innovation Solution
Determine the thermal-neutral cut location on resistors by measuring voltage deviations before and after laser pulses, allowing for trimming at this location to minimize thermally induced errors, and implement a process that adjusts resistance values in real-time to achieve high accuracy and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If laser trimming is performed on low-ohm resistors, then resistance values can be adjusted, but thermoelectric potentials cause significant measurement inaccuracies
Solution Approach 1:
The patent applies preliminary action by performing a test trim operation before the final trimming process. During this test trim, the system measures the thermoelectric offset voltage and uses it to calculate a corrected desired resistance value. This preliminary measurement and calculation enable the final trim to compensate for thermoelectric effects, achieving accurate resistance values despite the presence of thermoelectric potentials during trimming.
Solution Approach 2:
The patent implements feedback by continuously monitoring the resistance value during trimming and comparing it against the corrected desired value that accounts for thermoelectric offsets. The system uses this feedback information to adjust the trimming process in real-time, ensuring that the final resistance value achieves the target accuracy despite thermoelectric interference during the measurement and trimming process.
2Productivity
If tracking trim process is used to speed up resistor trimming, then productivity increases, but transient thermal effects cannot be corrected
Solution Approach 1:
The patent applies preliminary action by performing a preliminary test trim and measurement cycle before the final high-speed tracking trim. During this preliminary phase, the system characterizes the thermoelectric offset behavior. This preliminary characterization enables the subsequent tracking trim to operate at high speed while using pre-calculated compensation values to maintain accuracy, thus resolving the contradiction between speed and precision.
Solution Approach 2:
The patent changes the measurement parameters by using alternating current (AC) measurement techniques during the tracking trim process. This parameter change allows the system to distinguish between thermoelectric DC offsets and the actual resistance changes during trimming, enabling high-speed tracking trim to maintain accuracy by filtering out or compensating for the thermoelectric interference through parameter modification.
3Measurement precision
If measure/predict trim process is used to improve accuracy, then measurement precision increases, but processing time increases due to stabilization delays
Solution Approach 1:
The patent changes the measurement parameters by implementing AC measurement techniques and modified measurement timing sequences. Instead of waiting for complete thermal stabilization, the system uses AC measurements that can be taken during the transient phase, and employs specific timing sequences that capture resistance values at optimized moments. This parameter change reduces the required stabilization time while maintaining measurement precision through the use of differential measurements and thermoelectric offset compensation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables high-speed, accurate trimming of resistors by minimizing thermoelectric effects, ensuring consistent and precise resistance values across batches, and improving the accuracy of final resistance values in trimmed resistors.
Implementation Method 1
The laser trimming process raises the temperature of the resistor. This added heat affects the measured resistance due to the TCR of the resistor
Implementation Method 2
Offsets caused by the actual laser trimming are more difficult to correct, particularly for low resistance values. These errors are more difficult to correct because the transient effects caused by heating cannot be practically addressed in a tracking trim process
Implementation Method 3
laser-induced thermal electromotive forces (EMFs), and currents such as those caused by Seebeck and Peltier effects
Implementation Method 4
laser-induced thermal electromotive forces (EMFs), and currents such as those caused by Seebeck and Peltier effects
Data Source
AI summary
Thermoelectric effects that occur during laser trimming of resistors (20) are resolved by taking voltage measurements. The voltage attributed to laser heating on a resistor (20) during a low-power simulated trim (10) is used to determine a relatively thermal-neutral location (18) on the resistor (20). A trimming-to-value operation can then be performed on all like resistors (20). Voltage measurements can also be taken before and after every pulse in a trimming operation to establish thermal deviation information that can be used to offset the desired trim value against which resistor measurement values are compared. Spatially distant or nonadjacent resistors (20) in a row or column can also be trimmed sequentially to minimize heating effects that might otherwise distort resistance values on adjacent or nearby resistors (20).