flex pcb design guidelines

The purpose of this design guide is to enable you to design a highly reliable, flexible printed circuit optimized for manufacturability.

This guide provides technological data for choosing the appropriate materials, and recommendations for their correct design, while taking into account their integration criteria and constraints through assembly processes and car environment.

Below guildelines including these contents;

  • Flex pcb board standard stack up
  • Flexible pcb production process flow
  • Flexible circuit Design Guides and Rules

Flexible Circuit Board Types or Flex pcb Construction

Single Side Flexible PCB

Single Side Flexible PCB

 

flex pcb manufacturer

Double sided flexible circuit

Double sided flexible circuit

flexible pcb manufacturer

multilayer flexible pcbMultilayer Flexible PCB

flex pcb board

blind and buried via flexible circuit

laser drill flex pcb

Blind and buried via flexible circuit

Flexible circuit manufacturing process flow

Flex pcb flow chart

flex pcb board

Design Guides and Rules

1.Bonding Sheet Design (Folder area) 

Bonding Sheet Design (Folder area)

 

2. Pattern design of Folder Area

Pattern design of Folder Area

3.Silk Screen Specification

Silk Screen Specification

Silkscreen

 

4.Pattern line thickness & tolerance of raw material

Pattern line thickness & tolerance of raw material

5.Through hole / Pad (Inside )

Through hole / Pad (Inside )

6.Tear-drop design

Teardrop

7.Cover lay & Solder Resist Formative Dimension

Cover lay & Solder Resist Formative Dimension

8.Gap from stiffener edge to Hole

Gap from stiffener edge to Hole

9.Gold fingers design

Gold fingers design

10.Pattern Cover lay Open Area Specification

Pattern Cover lay Open Area Specification

11.Design in flex pcb bending areas

The bend radius calculation rule is explained in IPC-2223B: 
With as main objective to keep constraints lower than the FPCB copper elongation limit.

Flex pcb bending radius

12. flexible pcb dynamic bending 

Depending of the radius fold and cycles number needed the FPCB could be adapted. 
For example Hemeixinpcb builds and guarantee FPCB for 100000k cycles into a HDD, and 100k cycles into a mobile phone.

Some data are given for a FPCB double-sided tested with 5mm radius fold: 

  • PI of 12.5μm, copper of 35μm, coverlay of 12.5μm => 20k cycles 
  • PI of 25μm, copper of 17.5μm, coverlay of 25μm => 10k cycles
  • PI of 12.5μm, copper of 17.5μm, coverlay of 12.5μm => 90k cycles

The most Polyimide thickness used for the base material and for coverlay is 25 μm, but for applications needing more cycle in dynamic bending the use of 12.5 μm must be studied with manufacturer. It could rise cycle from 10k to 90k (with copper 17.5μm).

For boards subjected to dynamic bending thinner copper thickness improve the number of cycles. 17.5μm thickness copper is advised and must be studied with manufacturer. Decrease from 35μm to 17.5μm could rise cycle from 20k to 90k (with polyimide 12.5μm) 

In this case bend radius calculation (next chapter) must be done with EB=0.3 %

For boards subjected to dynamic bending, tracks on only one side improve number of cycle. If more layer of copper track is needed, staggered tracks are mandatory.

13.flexible pcb Static bending

For a natural static bending IPC advise not to place components in bending area but manufacturers tested favorably little and not fragile components. They advise to not place them into bending radius lower than 100mm. The placement in concave (inner radius) bending is less restrictive.

 

flexible pcb static bending

14.flexible pcb constraints areas
Each area in a flexible circuit has its constraints; the mechanical designer shall give description details depending on the final requirements.

flexible pcb constraints areas

hdi flex pcb

While using this guide, keep in mind that the design information provided is only a suggestion. Hemeixinpcb takes pride in manufacturing flex circuits that are considered difficult to build. In most cases, we do build above and beyond the “standard” circuit specifications, provided that the circuit design and type allow for it.

Hemeixin welcomes the opportunity to help you design and manufacture a product that meets or exceeds your expectations. That is why we have established a variety of communication channels to encourage meaningful exchange and dialog.  Please send email to sales@hemeixinpcb.com If you need some supports.