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Laser trimming is a manufacturing process that uses a laser to modify the operating parameters of an electronic component or a circuit by reducing the quantity of the component&#;s material incrementally.
A typical application of laser trimming is in adjusting the resistance of an unnecessary thin-firm or thick-film resistor by cutting away a smaller proportion of the resisting material.
This trim or cut increases the resistance of a component by narrowing or expanding the resistive material&#;s current path. Measuring the active resistance value of the material resistor while the trimming process continues is an accurate way of establishing the final results.
Besides, specific capacitors can be accurately laser trimmed to achieve an accurate capacitive. This is usually achieved by removing the upper layer on a multilayer capacitor to decrease its capacitance by reducing the top electrode area.
Laser trimming technology has many applications such as cutting metal plates. It also makes it possible to cut tiny holes and intricate shapes.
The laser trim process on stainless steel, mild steel, and aluminum plate is accurate, yields accurate cut quality, and produces a small heat affect zone and a small kerf width.
The laser beam comprises a column of highly intense light of a mono color or wavelength. For instance, of the CO2 laser, the wavelength is part of the Infra-Red light spectrum, thus making it invisible to the naked human eye.
The beam is about ¾ inch in its diameter as it passes from the resonator, emitting it through the beam path. The beam can be bounced in various directions using several mirrors and beam benders before focusing on a plate.
The focused laser beam passes through a nozzle before it hits the plate. Also, it flows through the nozzle right before it comes into contact with the plate. Besides, compressed gas also flows through the nozzle, for instance, Nitrogen or Oxygen.
A unique lens is used to focus the beam or even a curved mirror, which happens in the laser cutting gear head.
The beam is accurately concentrated such that the shape of the focus spot and the energy density around the spot is precisely round, centered from the nozzle, and consistent.
When a giant laser beam is focused down a single pinpoint, the heat density generated is exceptionally high. Take, for example, using a magnifying glass to concentrate the sun&#;s rays on a single tip of a reef to start a fire.
Now consider focusing over 6 KWatts of energy onto a single spot and how the spot becomes. The extreme power density causes rapid heating, melting, melting, and complete or partial vaporization of the heated material.
When trimming mild steel, the laser beam heat is enough to create a standard oxy-fuel heating process since the laser cutting gas is pure oxygen, just like any other oxy-fuel torch.
When trimming aluminum or stainless steel, the laser beam is used to melt the material while the laser cutting gas blows off the molten metal pieces of the kerf. When cutting using a CNC laser cutter, the laser beam source/ head is adjusted over the metal being cut, thus achieving the desired cut shape.
Typically, a capacitive height is used to control the system such that a very accurate distance is maintained between the plate being worked upon and the nozzle end.
This distance is equally important since it determines the focal point of the plate surface. Raising or lowering the focal point from above the plate surface greatly impacts the cut quality.
Other parameters that can affect the cut quality, such as a stable laser bean, reliable and extremely accurate cutting process, are properly controlled.
Laser trimming can be done in two ways: Active and Passive. Passive trimming involves adjusting a single component such as a capacitor or a resistor to a specific value.
If the trimming changes the entire circuit output, such as its frequency, voltage, or attenuation, this is described as an active trim. During the trimming process, the circuit output performance is actively monitored.
Once the desired output is achieved, the trimming process is automatically shut off. The process variability arises from the laser power based on the component level, laser spot size, wavelength, or pulse duration of the laser emitter.
Electrical contact is required to the component circuit to ensure feedback measurement in both active and passive trim. This is usually done through a dedicated probe card that uses either pressure pins or spring blades.
One advantage of laser trimming over mechanical cutting is that it has an easier work holding and reduced contamination of your workpiece( no cutting edges get contaminated by the resulting cut material.
Precision cuts and High accuracy. This is because the cutting laser beam doesn&#;t degrade during the cutting process. Besides, laser trimming uses a very powerful laser and extremely small laser, focusing the beam of light on the material&#;s surface.
No need to modify or replace tooling gears hence lower costs. Laser trimmers are economical to use even in limited run-projects. This is particularly true since the laser cutter does not need to use custom-build tools or modifications for your projects.
Easier to use. It would be best to have a laser cutter, material cut, and a schematic to load into your computer. This cuts down the overall cost even when working on small batch projects.
Can handle any complex job. There is no job complexity when it comes to the laser cutter. The high-powered laser beam can work even on the very narrow section of the material being cut, thus resulting in little or no warping and distortion.
Less wastage and high utilization of the material. Laser trimmers can utilize a significant percentage of your material, thus maximizing the overall usable components.
Besides, trimming is a useful approach for the semiconductor industry when establishing various devices in a mono wafer device design, also known as device derivatives or options in general terms.
It is incorporated with a metal fuse, a poly resistor Zener called analogue trim cuts.
Improving semiconductors through trimming. Laser alignment involves target modification of electronic circuit properties through link blasting or laser cuts.
For this reason, the alternative component is selected and processed using a laser. Lateral trimming into a resistor increases its resistance value.
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When it comes to capacitors, removing the upper cover electrode can significantly reduce capacitance.
Some passive trimmer utilizes a specialized pressure chamber to facilitate resistor trimming in a single phrase.
In this case, the LTCC boards are contacted using test probes on an assembly side and cutting done by a laser beam arising from the resistor side.
This cutting method does not require contact points between the two resistances due to the pitch adapter contact with the component on the other side of where the cutting occurs. This means it is possible to arrange LTCC less expensively and more compactly.
Trim potentiometers, also known as trim pots, tune, adjust and calibrate circuits. It is a type of adjustable potentiometer or variable resistor. These trim pots are used to calibrate circuits and equipment immediately after manufacturing.
Trim pots are not meant to be adjusted or seen by the device&#;s user. They are usually mounted directly on the circuit board and adjusted using a small knob or screwdriver. Some have expandable shafts that can be adjusted using fingers.
Designers use adjustable potentiometers during the end testing of a unit to determine the ideal performance units of a circuit. However, some end-users opt not to have potentiometers since they can easily drift, easily mis-adjust or sometimes develop noise.
Need laser trimming equipment for your operations? Drop us an enquiry with your requirements and we&#;ll get back to you with recommended options and cost estimates. Contact us now.
A laser module designer can use a fixed resistor, mechanical pot, digital pot, or a digital-to-analog converter (DAC) to control the laser driver's modulation and bias currents. The advantages of a programmable method (POT or DAC) are that the manufacturing process can be automated and digital control can be applied (e.g., to compensate for temperature). Using POTs can be a more simple approach than a DAC. There can be a slight cost advantage to using a POT, but this is usually not significant relative to other pieces of the design. Using a DAC can offer advantages, including improved linearity (translating to ease of software implementation and ability to hit the required accuracy), increased board density, a wider range of resolutions, a better optimization range, ease of use with a negative voltage laser driver, and unit-to-unit consistency.
This application note discusses the advantages of using these devices in these applications and provides an overview of the biasing circuit requirements in laser drivers.
Several families of laser drivers from a variety of vendors are designed to use resistors to control the modulation and bias currents supplied by the laser driver. Potentiometers and digital-to-analog converters (DACs) can also be used to control these parameters. With each control method, there are benefits and tradeoffs that will affect the overall laser driver's performance. To fully understand the advantages and disadvantages of the choices of laser driver control systems, some familiarity with laser drivers and fiber module design is essential.
Originally, resistors were used to control modulation and bias currents, as shown on many laser driver data sheets. While the least expensive component option, resistors don't allow real-time adjustments and tweaking them during the system calibration manufacturing step is difficult and time consuming. A better solution is to use a mechanical potentiometer (variable resistor), which allows manual adjustment.
As volumes increase and automation becomes important, the mechanical potentiometers can be replaced by digital potentiometers. Digital potentiometers also offer active digital control.
Active digital control is a technique of monitoring a parameter (such as output power) by measuring it with an ADC, processing it with a digital engine, and then using this information to adjust a parameter (such as laser driver output current). Active digital engines can compensate for the temperature dependence of laser diodes.
DACs can be used in most places that a potentiometer can be used, and can offer several advantages in some designs.
Many laser drivers have a very simple structure that translates the programming resistance (RPROGRAM) into the output bias and modulation depth currents (see Figure 1). Typically, the internal circuitry behind the laser driver current control pins (i.e., IMOD, IBIAS) includes an internal reference voltage source. The output current of this internal voltage source is measured, and amplified via a current amplifier, the output of which is the output of the laser driver. A simple resistor connected between ground and these control pins, provides a consistent control current for that circuit. Note that the laser driver only cares about the amount of current pulled out of this pin, not the value of the resistor connected to it. Hence, the resistor can be replaced by a DAC that controls this current, as will be described later. Typically, the gain of the current amplifier is on the order of 100-200 (mA/mA), and typical output currents are up to 50-80mA.
Figure 1. Laser driver internal architecture for sensing the value of the programming resistor.
Using a digital pot in place of the control resistor is the simplest and most obvious approach (see Figure 2).
Figure 2. Programming a laser driver with a digital potentiometer.
However, the resistance value of the available pots may not precisely line up with the desired range of programming current. Additional resistors can be used to more directly map the range of the pot onto the range of the currents desired (see Figure 3). Note that the current varies with the inverse of the resistance. Digital potentiometers usually have evenly spaced steps, which means that the resulting step size of the programming current will be large in the low resistance range of the pot, and small in the high resistance range.
Figure 3. Programming a laser driver current with an optimized programming range potentiometer.
A DAC can be used in place of a pot to control the laser driver currents. A voltage output DAC is used with a series resistor, such that the current drawn from the laser driver control pin is the programming current (see Figure 4). The ideal full scale/reference voltage for the DAC is the same as reference voltage internal to the particular laser driver. It can be larger, but the usable range of the DAC is compromised
Figure 4. Programming a laser driver current with a DAC.
Some of the reasons a design engineer would consider using a DAC include:
A laser module designer can use either a fixed resistor, mechanical pot, digital pot, or a DAC to control the laser driver's modulation and bias currents.
The advantages of a programmable method (POT or DAC) are that the manufacturing process can be automated and digital control can be applied (e.g. to compensate for temperature).
Using POTs can be a more simple approach than a DAC. There can be a slight cost advantage to using a POT, but this is usually not significant relative to other pieces of the design.
Using a DAC can offer advantages, including improved linearity (translating to ease of software implementation and ability to hit the required accuracy), increased board density, a wider range of resolutions, a better optimization range, ease of use with a negative voltage laser driver, and unit-to-unit consistency.
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