Flexible Printed Circuit Board Stiffeners
FPC with Stainless Steel Stiffener
In the flexible printed circuit boards (FPCB) manufacturing, stiffeners are a common requirement in a lot of flex circuit designs. An FPC stiffener is not an electrical part of the Flex Circuits, but plays a role of providing a mechanical support function. Stiffeners are a common requirement in a lot of flex circuit designs, and FPC stiffeners are materials added to a flex circuit to rigidize particular areas. Some rigidizing is recommended under SMT components, but not required. Some stiffeners are added on the FPC panel border, providing SMT support, like a SMT carrier. Some other areas applied stiffeners to consider rigidizing include:
- Hole Patterns
- Increasing bond strengths
- Meeting the requirements of zero insertion force (ZIF) sockets and connectors
- Increasing overall thickness
- Solder resistance, like solder mask
- Die attach platform for wire bonding components
- Heat dissipation
- Constraining bend areas to predefined locations
Stiffener Materials
FPC stiffener materials can be FR4, polyimide (PI) and stainless steel. The flex PCB stiffener refers to a stiffener attached to either primary side or secondary side of the FPC PCB. Different stiffener materials have different purpose and applications.
Polyimide (PI) Stiffener for Flexible Circuits
Polyimide can be the dielectric core material of FCCL, coverlay and stiffeners of flex PCBs and rigid-flex PCBs. PI stiffener is a good option of excellent solder resistance and high bond strengths. If you are familiar with flexible circuit boards with PI stiffeners, you are aware that the most preferred locations of the stiffeners are on the back side of insertion gold fingers. Sometimes, you can pick the part of PI stiffener not attached or laminated to FPC body, and you are easy to insert the FPC connector fingers into the ZIF connector or socket.
FR-4 Stiffeners in Flex Circuits
FR4 Stiffener in Flex Circuits
f your flex circuit utilizing a FR4 stiffener, it looks like a rigid-flex PCB. FR4 can be the CCL of rigid PCB, and it is the most common material applied for stiffeners in rigid-flex and flex circuits. The main purpose of adopting a FR4 stiffener include (1) providing flat enough support when the flex PCB in the pick-and-place and reflowing processes. (2) plated-through hole (PTH) components, the stiffener(s) need to be located on the same side of the flex from which the component is inserted to allow access to solder pads on the flex circuit. In some flex circuit prototype stage, customer wants to save cost in whole turnkey flex circuit assembly project, the flex circuit supplier is always been asked to add a FR4 frame on the border of the panelized PCB to replace the SMT carrier. When completing flex circuit assembly, the manufacturer will break and de-panelize them into single pieces, and the FR4 frame will be wasted.
In some flexible PCB designs, the hole diameters of FR4 stiffeners are the same as that of on FPC. The holes will be difficult to be attached, and may lead to dis-alignment. As a leading rigid-flex and flex circuit manufacturer, Fuchuangke Technology always recommends our customers to enlarge the holes on FR4 stiffener 0.3mm bigger than those related holes on FPC, then to ensure good alignment.
Stainless Steel Stiffeners In FPCB
Stainless steel stiffeners are with great features such as excellent corrosion resistance and form ability, compatibility, and robustness within a wide temperature range. The stainless-steel stiffeners in FPCBs (flexible PCBs) are always added to the connecting fingers to stiffen the FPCs in order to facilitate assembly. The common thickness is various from 0.1mm (4mil) to 0.45mm (18mil). The stainless-steel stiffeners need to be customized after working Gerber and MI issued, and the lead time of such kind FPCBs need extra 3-5 days.
Common-Used FPC Stiffener Thickness
| Stiffener Material | Usual Thickness | Unusual Thickness |
| FR-4 |
0.2mm(8mil) 0.3mm(12mil) 0.4mm(16mil) 0.5mm(20mil) 0.6mm(24mil) 0.7mm(28mil) 0.8mm(32mil) 1.0mm(39mil) 1.2mm(47mil) 1.5mm(59mil) |
0.1mm(4mil) 0.9mm(35mil) 1.1mm(43mil) 1.3mm(51mil) 1.4mm(55mil) 1.6mm(63mil) |
| Polyimide (PI) |
0.1mm(4mil), 0.15mm(6mil), 0.2mm(8mil), 0.25mm(10mil) |
0.075mm(3mil) 0.125mm(5mil) 0.175mm(7mil) 0.225mm(9mil) 0.275mm(11mil) |
| Stainless Steel |
0.1mm(4mil) 0.15mm(6mil) 0.2mm(8mil) 0.25mm(10mil) 0.3mm(12mil) 0.35mm(mil) 0.4mm(16mil) 0.5mm(20mil) 1.5mm(59mil) |
0.45mm(18mil) |
Quick Quote
Click the Quick Quote buttons below, you can turn to the different PCB quote pages. Just fill in the PCB specifications, upload Gerber files, BOM, Assembly Drawing and Pick-and-Place file, you will get quick quote of PCB board and PCB Assembly.
