1. Material properties and selection
High TG base material requirements
Tg value: ≥170°C (130~140°C for conventional FR-4), typical materials include:
Isola FR408HR (Tg=180℃, Dk=3.8, Df=0.010@1GHz)
Shengyi S1000-2M (Tg=175°C, cost 30% lower than imports)
Thermal Stability:
T288 heat-resistant time: ≥60 minutes (5~15 minutes for conventional FR-4), preventing delamination by multiple reflow soldering.
Z-axis CTE: ≤50 ppm/°C (60~80 ppm/°C for conventional FR-4), reducing the risk of thermal cycling hole wall fracture.
Thick Copper Foil Specifications
Copper thickness range: 2~10 oz (70~350 μm), selected according to current demand:
2~3 oz: for DC-DC converters, motor controllers (carrying 20~50A current).
4~6 oz: High power inverter, power bus (carrying more than 100A current).
10 oz: Extreme scenarios (e.g. welding machine, energy storage system), special etching process required.
2. Design Specifications and Core Challenges
Key points of line design
Line width/spacing compensation:
Thick copper etching side corrosion is serious, need to increase the line width compensation (e.g. 3 oz copper foil needs to be extra 20%~30% wider).
Minimum pitch: ≥8mil (200μm, 3 oz copper foil) to prevent short circuit.
Current carrying capacity optimization:
Current Carrying Capacity Calculation: Based on IPC-2152 standard, 3 oz copper foil, 10℃ temperature rise, 100mil line width can carry about 30A DC.
Copper Foil Topology: Laying copper in a grid pattern or localized thickening (copper block embedding) is used to reduce resistance and heat buildup.
3. Reliability Test Criteria
Thermo-mechanical reliability:
Tg test: DSC method (Differential Scanning Calorimetry) to verify the actual Tg ≥ nominal value.
Thermal cycle test: -40℃~150℃, hole resistance change <5% after 1000 cycles (IPC-6012 standard).
Current load test:
Continuous current load: 1000 hours of continuous operation at rated current, temperature rise <40℃.
Instantaneous overload: 2 times rated current impact (1 second/time, 100 times), no burnout or delamination.
4. Typical application scenarios
New energy vehicle OBC (on-board charger)
Industrial inverter
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