SP200501 – RO4350B Starting Point Compensation Factors
RO4350B laminates are engineered for high-frequency applications requiring a balance of cost, performance, and reliability. The following starting point compensation factors are intended to assist fabricators in achieving optimal processing results while minimizing dimensional variations during manufacturing.
1. Purpose of Compensation Factors
- Dimensional Stability: Ensure accurate registration and alignment during multilayer construction.
- Consistent Electrical Performance: Maintain predictable dielectric properties.
- Manufacturing Tolerance: Address changes due to processing stresses such as etching, lamination, and thermal cycling.
2. Key Compensation Guidelines
- Panel Size: Factor in dimensional changes for large panel sizes to reduce misalignment in etching and drilling.
- Copper Foil Adhesion: Use consistent surface treatment to stabilize copper-to-laminate adhesion during thermal cycling.
- Dielectric Constant Variations: Account for minor shifts in dielectric constant due to resin flow or processing temperatures.
3. Dimensional Change Data
| Process | Expected Dimensional Change | Compensation Suggestion |
|---|---|---|
| Etching | Up to 0.1% reduction (in x/y dimensions) | Increase artwork dimensions slightly |
| Lamination | Negligible but stress-induced distortion | Use balanced construction designs |
| Thermal Cycling | Expansion < 0.05% | Use pre-bake steps to stabilize |
4. Processing Recommendations
- Material Pre-Conditioning:
- Bake RO4350B panels at 250°F (121°C) for 1-2 hours before fabrication to remove residual moisture and thermal stresses.
- Layer Registration:
- Monitor alignment shifts during etching and multilayer lamination. Apply a 0.05-0.10% compensation to artwork to account for material flow.
- Drilling Compensation:
- For plated-through holes, compensate for minor shrinkage in drill patterns by using appropriate tool sizes and process alignment checks.
- Thermal Relief Design:
- Use optimized pad geometries to minimize localized expansion or contraction around copper features.
5. Electrical Compensation Factors
| Frequency | Dielectric Constant (Dk) | Recommended Adjustments |
|---|---|---|
| Low Frequency (<1 GHz) | 3.48 ± 0.05 | No adjustment needed |
| Mid Frequency (1-10 GHz) | 3.66 ± 0.05 | Tweak trace widths ±2-5% |
| High Frequency (>10 GHz) | 3.74 ± 0.05 | Narrow traces slightly |
6. Verification and Testing
- Post-Processing Inspection: Measure panel dimensions after etching and lamination to verify adherence to expected tolerances.
- Electrical Testing: Confirm Dk values through impedance measurements and adjust artwork compensations iteratively if required.
- Thermal Stability Tests: Perform thermal cycling and inspect for delamination or dimensional distortions.
RO4350B laminates offer robust high-frequency performance but require careful handling and compensation during fabrication. By applying these starting point compensation factors, fabricators can ensure high-quality, reliable circuits with minimal rework or performance deviation.
