Flex to Install Bare Board or Assembled PCB’s

Made in Europe

Eurocircuits’ PCB SEMI-FLEX pool is a solution for flex to install PCB’s, typically 4 layers, made entirely of FR4.

Unlike conventional flex-rigid PCB’s, the flexing element is not polyamide but a thin FR4 core with two layers of copper specially treated to flex without cracking.

What’s Available

  • Bare Board or Assembled PCB’s
  • Bare Board PCB’s in 7 Working Days* or Assembled PCB’s in 12 Working Days*
  • See Tables Below for Available Specifications
  • No Tooling Charges
  • No Minimum Order Charge.
  • 100% Manufacturability Check Prior to Production
  • PCB Configurator to check and upload design parameters before pricing
  • PCB Checker to analyses your data before you place your order
  • BOM and CPL analysis


SEMI-FLEX is a flex to install PCB, typically 4 layers, made entirely of FR4. Unlike conventional flex-rigid PCB’s, the flexing element is not polyamide but a thin FR4 core with two layers of copper specially treated to flex without cracking.


SEMI-FLEX is flex to install. Unlike polyamide, the FR4 core is not capable of continuous flexing.

However it will bend a limited number of times (typically 5 – see the technical specification below) at a controlled radius and to any angle.

This makes it an ideal solution where you need to mount two PCB’s in a unit at an angle to each other. Instead of using connectors and cables or a composite flex-rigid PCB, you can design a single FR4 SEMI-FLEX PCB which can be safely bent a sufficient number of times to allow installation and subsequent maintenance as needed

Eurocircuits’ SEMI-FLEX pool

Eurocircuits’ 4-layer SEMI-FLEX PCB’s use a 100 micron central core for the flex area, with 35 micron high-ductility copper foil on each side.

The stack is then made up on each side with a 510 micron FR4 core and two layers of no-flow prepreg (see the full technical specification below).

An alternative technology is to build a 2- or 4-layer PCB and then depth-mill the material away to leave a thin section as the flex area.

We have adopted the core solution even though it needs more operations and so is a little more expensive. It gives a symmetrical build and so a more stable board, while depth-milling is difficult to control meaning that the flex area may have an irregular thickness.

With a core-build we through-mill (rout) the prepreg before pressing. We can then rout the outer layers with any minor variation in cutter depth being absorbed by the void.

SEMI-FLEX in Production Panel

Free On Line Price Button

The core build makes it easier to design a main board with up and down sections or a final Z-configuration.

SEMI-FLEX boards are preferably supplied in a panel to avoid any damage during transport or assembly.

SEMI-FLEX Buildup Drawing

SEMI-FLEX pool Service Parameters

 Minimum Bend Radius

 5 mm

 Maximum Bend Angle


 Maximum Number of Bends


 SEMI-FLEX length Calculator

 (2 x pi x bend radius) x (bend angle/360)

For example, bending 5 times over an angle of 180 degree with a radius  of 5mm requires a minimum length of the semi-flex part of 15,7mm

SEMI-FLEX Bend Radius Drawing

 Copper thickness on SEMI-FLEX Core

 35µm high ductility copper

 Highest Pattern Class

 Class 6 – 150µm track/gap (to accommodate the bending)

 Drill Holes

 Not allowed

SEMI-FLEX No Drill Area

 Slots and cut-outs

 Not allowed

 Corners in SEMI-FLEX Area Profile

 Minimum radius 1.00mm

SEMI-FLEX Corner Profile

 Corner where a Narrow SEMI-FLEX Area Joins Rigid Area

 Minimum radius 1.00mm


 Use copper on both sides


Use copper pour around tracks where possible



 Yes – At each end of the Semi-Flex Material

 Minimum Size

Width of Semi-Flex Material or 5mm x 5mm whichever is the greater

 Material (rigid and semi-flex cores)

FR4 Improved High Tg

Isola FR406N

 Number of Copper Layers


 Board Thickness

 1.55mm (see build map)

SEMI-FLEX Core Thickness


 Outer Layer Start Copper Foil


Min. Track Width/Spacing


Min. Finished Hole Size

 PTH 0.100mm

 NPTH 0.200mm

 Surface Finish

Pooling – ENIG, IM Ag






 Break-routing or V-cut

 Slots and Cut-outs (milling)

Tool sizes – 0.5, 1.2, & 2.0mm – in Rigid Area Only

 Advanced Technologies Allowed

Pooling – Peelable mask, PTH on board edge, Round edge plating, Copper up to board edge, Heatsink paste, Via filling,  Edge Connector Gold

Non-Pooling – Carbon pads

 Advanced Technologies Not Allowed

Blind & Buried vias

 UL Marking

Not yet available

 Delivery Format

Preferably delivered in a panel for safe handling

SEMI-FLEX pool Assembly Service Parameters

Number of Component Layers

1 or 2


1 PCB and up

Lead Time

12 working days* (7 for manufacture and 5 for assembly)

Minimum PCB Dimensions

Width of Semi-Flex Material or 5mm x 5mm – whichever is the greater

Maximum Customer Panel

326mm x 426mm

Assembly Type

SMT – single or double sided

THT – single or double sided

SMT + THT Mixed Technology – single or double sided


Passive Components  – 0201 and higher

Active Components – from 0,35mm pitch

BGA – 0,4mm pitch and above

Solder Alloy

Basis SAC 305 Sn 96,5 Ag3 Cu 0,5 lead-free

Solder Paste Stencil

Laser cut

(included in the assembly cost – not delivered with the assembled boards)

Component Sourcing

All Components Sourced by Eurocircuits

(Components not sourceable by Eurocircuits can be supplied by the customer)

Quality Inspection

Visual inspection

Solder Paste Inspection (SPI)

BGA Placement

X-ray Inspection


  1. Subject to design meeting our SEMI-FLEX pool manufacturing and assembly specification and component availability.
  2. The price cannot be automatically calculated for a PCB containing more than 200 BOM lines or 1000 component placements, our engineering department will evaluate and send you an offer usually within 24 hours.
  3. These conditions are available in our calculator/Visualizer and will only be confirmed in our order confirmation.