What is Flexible PCB Coverlay?

Flexible PCB coverlay protects the wiring on bendable circuit boards. Think of it like flexible “armor” for your circuits!

• Why it’s needed: Standard solder masks (the coating on rigid boards) aren’t bendy enough for flexible PCBs.
• What it does: It covers and shields the copper wires, preventing damage during bending or soldering.
• Key benefits: Excellent flexibility (moves with the board), Strong insulation (high dielectric strength), Durable protection

It’s the go-to solution in the industry for protecting flexible circuits!

What is Flexible PCB Coverlay Made Of?

Flexible coverlay is a protective sheet with two layers:

1. A sticky glue layer (acrylic or epoxy-based)
2. A strong plastic layer (polyimide)

It’s applied like a protective sticker:

• The glue bonds the plastic to the circuit board
• Heat and pressure seal it over the wiring

Thickness Choices:
Coverlay comes in different thicknesses for glue and plastic. The most common is equal thickness (ex: 0.001″ plastic + 0.001″ glue). Your choice depends on:

• Bendiness needed (thinner = more flexible)
• Weight of copper wires
• Required insulation strength
• Budget

Key Features:

Available in multiple thicknesses for different bending needs

Usually brown (natural polyimide color)

Excellent insulation: Blocks ~3,000 volts per 0.001 inch of thickness

Available in multiple thicknesses for different bending needs

How thick is flexible PCB coverlay?

Most coverlay uses a standard thickness:

• 0.001 inch of plastic (polyimide) layer
• 0.001 inch of adhesive (glue) layer

Thinner or thicker options exist for special cases:

• 0.0005 inch (half the standard thickness) for maximum flexibility
• 0.002 inch (twice as thick) for extra protection

These are only used when the design needs them.

What’s the difference between flexible PCB coverlay and solder mask?

Both protect and insulate the outer wiring on bendable circuit boards, but they work differently:

• Coverlay: A solid sticker-like layer (usually polyimide plastic + adhesive).
• Solder mask: A liquid paint-like coating (flexible version exists).

Though they serve the same main job-shielding circuits-each has unique features. Your choice depends on the board’s design needs.

Flexible PCB Coverlay vs. Solder Mask

1. Material:
   • Coverlay = Solid layer (adhesive + polyimide plastic)
   • Solder Mask = Liquid-based coating
2. Dam Size (Barrier Between Pads):
   • Coverlay dams: ≥10 mils (0.010″)
   • Solder mask dams: ≥4 mils (0.004″)
     → Dams block liquid solder from spreading between pads.
3. Trace-to-Opening Clearance:
   • Coverlay: Can be as small as 3 mils
   • Solder Mask: Needs ≥4 mils (smaller gaps cause defects)
4. Where Used:
   • Coverlay: Flexible/bendable areas
   • Solder Mask: Rigid sections
     Exception: Coverlay on rigid boards requires special access openings.
5. Compatibility:
   • Coverlay: Cannot protect very small parts (pitch components)
   • Solder Mask: Works for all component sizes

Flexible PCB coverlay effectively protects and insulates the outer wiring of bendable circuit boards, meeting different design needs. Understanding how coverlay differs from solder mask helps you design better flexible PCBs!