Inputs
- Pad width
- Pad height
- Pad pitch
- Base clearance
- Registration tolerance
- Adhesive allowance
- Minimum bridge
FPC / PCB Engineering Calculator
Coverlay Opening Calculator
Estimate coverlay opening size and bridge width from pad size, registration and adhesive allowance.
How to use the Coverlay Opening Calculator
Coverlay opening design affects pad exposure, registration tolerance, adhesive overflow and soldering reliability. This calculator estimates opening size and bridge width from practical process allowances.
Coverlay opening allowance
Formula: Opening size = pad size + 2 x (clearance + registration + adhesive allowance)
- Pad size: copper pad width or height.
- Clearance: desired exposed margin around the pad.
- Registration: coverlay-to-copper alignment tolerance.
- Adhesive allowance: allowance for adhesive squeeze-out or flow.
Formula Basis
- Formula basis: practical DFM allowance stack using pad size, clearance, registration tolerance and adhesive flow allowance.
- Engineering note: final coverlay opening and bridge rules should come from manufacturer capability and lamination trials.
Example
A 0.6 x 1.2 mm pad with 0.2 mm total allowance per side gives a 1.0 x 1.6 mm coverlay opening.
Outputs
- Recommended opening width
- Recommended opening height
- Allowance per side
- Bridge width estimate
Engineering Notes
- Small coverlay bridges can tear, shift or create adhesive squeeze-out problems.
- Connector pads and fine pitch pads often need factory-specific coverlay rules.
- For production release, verify pad exposure after lamination and coverlay registration.
Validation Checks
- Pad exposure
- Coverlay bridge width
- Adhesive overflow
- Alignment tolerance
Related Manufacturing Process
- Coverlay / Solder Mask - Opening compensation, bridge width, pad exposure, alignment tolerance
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FAQ
Why add adhesive allowance?
Coverlay adhesive can flow during lamination. Leaving allowance reduces the risk of adhesive covering solderable pad area.
Is the bridge width final DFM?
No. It is a quick estimate. Minimum coverlay bridge depends on material, thickness, tooling and factory capability.