Double Layer Flex Circuit With Exposed Gold Contact Pads
A double layer polyimide flex circuit with an array of exposed circular contact pads. Two conductive layers let the circuit route underneath its own contact area, which is what keypad, membrane switch and dome contact assemblies need.
What This Board Is
A keypad flex has a problem a ribbon does not: every contact needs a trace, and the traces cannot cross. On a single layer part that limits the number of keys. With two layers the routing drops below the pad array and the key count stops being a constraint. The pads themselves are plated for contact rather than for soldering, and our flex line offers plated or immersion tin, plated or immersion gold, and OSP.
Coverlay is opened selectively over the contact array, then the pads are plated or ink coated.
- Flex PCB
- 2 layer
- See specification
What You Get From This Build
- Two conductive layers route beneath the contact array, removing the key count limit of single layer designs
- Selective coverlay opening exposes only the contact pads and leaves the rest of the circuit protected
- Gold contact plating resists the wear and oxidation that repeated key presses cause
- Carbon ink and silver paste are available for contact surfaces where gold is not required
Who Specifies This Board
- Membrane keypad and control panel manufacturers
- Appliance and HVAC control builders
- Medical device makers with sealed operator panels
- Instrument manufacturers replacing a rigid keypad board with a sealed flex
Four Failures This Build Is Designed Against
Each one is a real way this class of board goes wrong, and the tolerance or process decision that prevents it.
Key count limited by single layer routing
Two layers put the routing under the pad array, so the pad count is limited by panel area rather than by how many traces can squeeze between contacts.
Keys that stop responding after months of use
Contact pads are plated rather than bare copper. Gold, tin, carbon ink and silver paste are all available depending on the contact mechanism.
Moisture reaching the circuit through the panel
Coverlay is laminated over everything except the intended contact openings, so the conductor is sealed across the rest of the part.
Gold plating an entire keypad circuit
Only the contact area needs a contact-grade finish. Carbon ink is used where the switch mechanism allows it.
Technical Specification
Product detail from the catalogue record, followed by the published process capability for the Flex PCB family. Anything the legacy catalogue did not record is marked TBC rather than filled in.
| Item | Technical specification |
|---|---|
| Product name | 2 Layer Flexible PCB |
| Legacy catalogue reference | 2 Layer(FPC) |
| Product family | Flex PCB |
| Layer count | 2 layer |
| Surface finish | See specification |
| Layer count | Single layer, double layer and multilayer |
| Base material | PI, FR4, PET |
| Base copper thickness | 9, 12, 18, 35 and 70 µm |
| Maximum board size | 406 x 610 mm (16 x 24 in) |
| Minimum hole, drilled | φ0.1 mm (0.004 in) |
| Minimum hole, punched | φ0.5 mm (0.02 in) |
| Plated hole tolerance | ±0.05 mm (±0.002 in) |
| Minimum track width | 0.05 mm (2 mil) |
| Minimum track gap | 0.05 mm (2 mil) |
| Surface treatment | Plated or immersion tin, plated or immersion gold, OSP |
| Outline treatment | Precise V-cut, punch, milled, laser outline |
| Outline tolerance | ±0.05 mm |
| Coverlay | PI film and PET film lamination |
| Solder resist inks | LPI soldermask, UV-cured soldermask, legend ink, peelable soldermask, carbon ink, silver paste |
| Peeling strength | 1.0 kgf/cm with adhesive copper, 0.5 kgf/cm with adhesiveless copper |
| Legend colours | Multiple silk-screen colours |
What The Board Is Made Of
| Material | Specification |
|---|---|
| Base material | PI, PET or FR4 |
| Base copper | 9, 12, 18, 35 or 70 µm |
| Coverlay | PI film or PET film lamination |
| Solder resist | LPI, UV-cured, peelable mask, legend ink, carbon ink or silver paste |
| Adhesion | 1.0 kgf/cm with adhesive copper, 0.5 kgf/cm adhesiveless |
What Can Be Changed
- PI, PET or FR4 base material
- Base copper from 9 to 70 µm
- Stiffeners in any number of positions
- Plated or immersion tin, gold, or OSP
- Carbon ink and silver paste contact printing
- V-cut, punch, mill or laser outline
How This Board Is Made
Eight stages on equipment sourced from the USA, Japan, Germany and Israel. Every stage listed runs inside our own plant.
Material selection
PI, PET or FR4 base chosen against whether the part is soldered and how often it flexes.
Imaging and etching
Circuit etched to a 0.05 mm minimum track and gap.
Coverlay
PI or PET film laminated over the conductors with openings cut at the contact areas.
Stiffeners
Laminated where connector tails or component areas need to be held rigid.
Hole forming
Drilled to φ0.1 mm or punched to φ0.5 mm depending on the feature.
Surface finish
Plated or immersion tin, plated or immersion gold, or OSP.
Contact printing
Carbon ink or silver paste printed where a contact pad needs it.
Outline
Precise V-cut, punch, mill or laser to ±0.05 mm.
What Is Checked Before It Ships
- Peeling strength of 1.0 kgf/cm on adhesive copper and 0.5 kgf/cm on adhesiveless copper
- Outline tolerance verified at ±0.05 mm after punching or laser cutting
- Coverlay opening registration checked against the contact areas
- Plated hole tolerance held at ±0.05 mm
- Stiffener thickness checked against the connector insertion specification
What The Plant Holds
- ISO 9001:2000. Quality management system certification recorded by the company. Current revision year available on request.
- ISO 14001:1996. Environmental management system certification recorded by the company.
- UL. Certification recorded by the company. File number available on request.
- RoHS and lead free. Listed in the company environmental policy alongside pollution prevention and resource reduction.
Certificate numbers, issue dates and current revision years are not published on the legacy site. Ask for copies with your enquiry and they will be sent with the quotation.
How It Compares With The Alternatives
Three boards from our own catalogue, side by side, so the trade-off is visible rather than argued.
| Board | Layers or build | Finish | Best suited to |
|---|---|---|---|
| 2 Layer Flexible PCB | 2 | See specification | Keypad and contact pad flex circuits |
| 1 Layer Flexible PCB | 1 | See specification | Shaped harness replacement circuits |
| FPCB Assembly With Antenna Coil | 1 | See specification | Flex circuits delivered fully assembled |
What To Send With Your Enquiry
Four things that decide whether the quote comes back right the first time.
- Mark the coverlay openings on their own layer, separate from the solder mask layer.
- State the contact finish you want on the pads and whether the rest of the circuit differs.
- Give the dome or membrane part number so the pad diameter and gap can be matched.
- Tell us whether the tail is soldered or inserted into a connector, since the two need different finishes.
2 Layer Flexible PCB Questions
Which contact finish should I use for a membrane keypad?
Carbon ink is standard where a conductive dome or a printed shorting pad is used. Gold is chosen where the contact carries a low level signal or must survive very high cycle counts.
Can you print silver paste on flex?
Yes. Silver paste and carbon ink are both listed in our flex capacity table alongside the LPI and UV-cured solder masks.
What is the minimum gap between contact pads?
Minimum track and gap on our flex line are both 0.05 mm, which is 2 mil.
Can this circuit be supplied already assembled?
Yes. We assemble flexible circuits as well as rigid boards, and our PCBA range includes flex assemblies.
Other Boards In The Flex PCB Family
Boards built on the same line, with the same tolerances, in a different configuration.
Single Layer Flex Circuit With Branched Arms And ZIF Tail
Single Layer Flex Ribbon With Parallel Conductors And End Stiffeners
Double Sided FR4 Board With Lead Free HASL
Four Layer Immersion Gold Board For Dense SMD Routing
Where This Board Is Used
The fields the legacy catalogue records for this class of board.
This Board In Context
Background Reading
Flexible circuits fail in ways rigid boards do not: creases in the wrong place, copper fatigue at a fold, tails that buc...
Design rules are usually set once and copied between projects. That is fine until a board needs to shrink, at which poin...
Get 2 Layer Flexible PCB Priced Against Your Own Files
Send Gerber RS-274X with an NC drill file, or an ODB++ package, with the layer count, thickness, copper weight, surface finish and quantity. We check it against the published capability before quoting.