Metal foil resistor is a high-precision, low temperature coefficient resistor element, whose core is to achieve stable resistance by combining metal foil with insulating substrate and forming a precision circuit. The following is a detailed analysis of its main production process, unfolded in the order of the flow:
Substrate pretreatment
Substrate selection: Ceramic (such as 96% alumina) or glass fiber reinforced epoxy resin board is usually used as the insulation substrate, which needs to have high thermal conductivity, low thermal expansion coefficient, and good mechanical strength.
Surface cleaning: Remove grease, oxides, and impurities from the surface of the substrate through chemical etching or plasma cleaning to ensure the bonding quality between the metal foil and the substrate.
Preparation and bonding of metal foil
Metal foil selection: commonly used nickel chromium alloys (such as Nichrome), manganese copper alloys (such as constantan), or pure metals (such as platinum), choose according to the requirements of resistance stability and temperature resistance.
Foil processing: Metal foil needs to be rolled to a micrometer thickness (usually 0.05~0.2mm), and an initial circuit pattern is formed through photolithography or chemical etching.
Adhesive process: High temperature epoxy resin adhesive or conductive adhesive is used to bond the metal foil to the substrate, and pressure and temperature (such as curing at 150-200 ℃) need to be controlled to avoid bubbles or delamination.
Graphic processing
Lithographic etching:
Apply photoresist and expose the defined resistance pattern, and remove excess parts through development.
Etch the metal foil to the target thickness and shape using acidic or alkaline solutions (such as FeCl ∝) with an accuracy of ± 0.01%.
Laser tuning: Fine tune the etched resistance with laser, changing the cross-sectional area or length through local ablation to achieve resistance tuning (with an accuracy of up to 0.01%).
Electrode and lead fabrication
Electrode deposition: Forming conductive electrodes at both ends of a resistor through electroplating (such as nickel, tin) or sputtering processes to ensure low contact resistance.
Lead connection: External leads are fixed to electrodes using soldering (such as tin lead solder) or crimping techniques, avoiding virtual soldering or stress concentration.
Encapsulation and Protection
Insulation coating: Coating the resistor with epoxy resin or silicone to provide mechanical protection, moisture resistance, and insulation performance.
Shell packaging: Some high reliability products may be equipped with metal or ceramic shells to further enhance their anti-interference ability.
Testing and screening
Resistance verification: Use a high-precision bridge to measure the actual resistance value and eliminate components with deviations exceeding the standard.
Stability testing: Conduct high-temperature aging, temperature cycling, and other tests to verify long-term reliability.
Parameter grading: Classify according to indicators such as resistance and TCR (temperature coefficient) to meet different application requirements.
Key process characteristics
High precision control: The uniformity of metal foil and etching process directly affect the consistency of resistance.
Temperature stability: The alloy composition and packaging design jointly determine the TCR index (up to ± 1ppm/℃).
Low noise characteristics: Non inductive design and metal foil structure reduce parasitic parameters, suitable for precision circuits.
Innovation direction
In recent years, the use of nanoscale metal alloy foils and photonic crystal etching technology has further improved the performance limit of metal foil resistors, especially in the fields of aerospace, medical electronics, and other areas where there is a significant demand.
This process combines materials science, micro nano machining, and reliability engineering to ensure that metal foil resistors can maintain excellent performance even in extreme environments.