I. Raw Material Input Control (Preventing Spillage and Defects at Source)
1. NTC Chips: Verify the resistance value of R25, B value, tolerance; Conduct sampling aging tests to avoid batch drift; Pay special attention to checking for micro-cracks in the glass and damage at the lead root of the glass-sealed chips.
2. Wire Materials, Insulation Tubes, Epoxy Resin/Silicone: Must meet temperature resistance, flame retardancy, and aging resistance (as required by home appliance safety standards, V0 flame retardancy); Need to be resistant to water vapor and hydrolysis in scenarios such as hot water kettles, dishwashers, and washing machines; Select 304 stainless steel for the metal shell to prevent rust and contamination.
3. Auxiliary Materials: Use low-residue, non-corrosive flux; Residual acid will slowly corrode the solder joints, causing open circuits or resistance drift over time.
II. Welding Process (Most Likely to Cause Soldering Defects, Chip Thermal Damage)
1. Strictly control the soldering iron temperature and welding time: Generally ≤ 300℃, welding time within 3 to 5 seconds; For glass-sealed NTC chips, add a heat dissipation clamp at the lead to prevent heat from being conducted to the chip, causing permanent drift or glass cracking.
2. Do not bend the leads near the chip root: Bend at least 2mm away from the glass-sealed body to avoid micro-cracks at the sealing area and prevent water ingress and moisture absorption in the future.
3. Appearance of solder joints: Bright and full, without soldering defects, false soldering, cold soldering, or excessive soldering; Conduct tensile strength tests for each batch, ensuring the solder joint’s tensile strength meets the standard to prevent vibration-induced breakage during use.
4. Cleaning: Clean the residual flux after soldering; Residual flux absorbing moisture will cause leakage and decreased insulation.
III. Packaging and Sealing/Thermal Shrinkage Process (Waterproofing, Insulation, Stress Control, High-Occurrence Fault Points in Home Appliances)
1. Selecting sealing glue: Use flexible silicone for high-temperature home appliances (oven, water heater), avoid hard epoxy; Hard glue will compress the chip during thermal expansion and contraction, causing stress drift and cracking.
2. Sealing process: Ensure thorough defoaming, no bubbles; Bubbles will reduce insulation and cause water ingress; Strictly control the curing temperature and time, incomplete curing will gradually absorb water.
3. Thermal shrinkage tubes: Heat evenly, ensure the tubes are completely tight against the body, without wrinkles or gaps; The cut edges of the tubes must not damage the insulation layer of the wire.
4. Metal shell assembly: The thermal filler material (thermal conductive silicone/gel) between the probe and the shell should be evenly distributed to ensure a rapid thermal response, while avoiding water accumulation in the gaps; The sealing of the shell must be tight to prevent water vapor from penetrating.
> Key Point: The thermal expansion coefficient of the packaging materials should match that of the chip and leads; otherwise, sealing failure and resistance drift will occur during high and low temperature cycles.
IV. Electrical and Performance Testing (Must be tested on the production line, 100% full inspection)
1. Resistance Test: Fix the temperature in a constant temperature bath (25℃) to measure R25, verify the resistance value and B value, and eliminate products with excessive tolerances; Pay attention to waiting for thermal equilibrium to avoid unstable temperature causing misjudgment.
2. Insulation Resistance: Measure the resistance between the lead and the metal shell with DC 500V; Insulation resistance should be ≥ 100MΩ.
3. Voltage Resistance (Electrical Strength): According to home appliance GB4706 standards, generally AC 1500V, 1 minute, no breakdown, flashover, or excessive leakage current; The production line can use short-time high-voltage accelerated testing (to verify equivalence).
4. Conductivity Short Circuit Test: Check for open circuits and short circuits.
5. Sampling for thermal response time test: Ensure the temperature response speed meets the requirements of the entire machine (water heaters, wall-mounted furnaces have high requirements for response speed).
V. Reliability Verification (Batch Sampling, Simulating Long-Term Use of Home Appliances)
For each batch, sample products are tested for reliability to detect potential hazards in advance:
- High and low temperature cycles (such as -40℃~125℃, several hundred cycles), test the resistance value after the cycle, and the drift should not exceed the standard.
- Wet heat aging: 85℃/85RH for a long time of aging, observe changes in insulation and resistance (focus on dishwashers and water heaters).
- Vibration and bending tests: Perform stress release on the root of the wire (pulling the wire, repeated bending), to prevent breakage of the entire machine during use.
- Water immersion/waterproof test (waterproof household appliances), salt fog (damp environment in kitchen and bathroom)
- Self-heating test: Control the working current to avoid temperature measurement errors caused by the sensor heating itself
Six. Mechanical and Structural Notes
1. Design stress release bends at the root of the wire; do not pull forcefully; vibration conditions are prone to causing the wire to break at the root.
2. Remove burrs from the edge of the metal probe to prevent puncturing the wire insulation.
3. Terminal crimping: Ensure a secure crimp; do not break the copper wire; the insulation at the crimping area should be fully covered to prevent leakage and short circuit.
Seven. Marking, Traceability and Safety Standards
1. Screen printing/labels: Model, resistance value, B value, temperature resistance, manufacturer information, clear and resistant to wiping;
2. Batch traceability: Retain each batch of raw materials, production records, test data;
3. Safety certification: CQC/UL, etc. The materials and structure comply with GB4706, GB/T14536.10, and the creepage distance and electrical clearance meet the safety standards for household appliances.
Post time: Sep-29-2026