How many types of stiffener for flex pcb?

Have you ever been faced don’t how to choose a suitable stiffener for your flex circuit board issue? Do you know t how many types of stiffener will be used for flex pcb? What is the reason why we need to add the stiffener on the flex PCB? Today let us study flex circuit board different types of stiffener together.

The types of FPC stiffener

In generally, there are only 3 types of stiffener we usually used. Polyimide(PI), FR4, and stainless.

1.Polymide PI stiffener:The tolerance can be controlled +/-0.03mm, high precision and have high temperature resistance(130~280 Centigrade)

2.Stainless Stiffener: Need to do assembly by hand and the process is more complicate, the cost will be a little higher.

3.FR4 stiffener: If the thickness is below 0.1mm, the tolerance can be controlled +/-0.05mm. If the thickness is more than 1.0mm, the tolerance is +/-0.1mm

Stiffener thickness:

1.PI stiffener thickness: 0.075mm, 0.1mm, 0.125mm, 0.15mm ,0.175mm, 0.2mm , 0.225mm, 0.25mm.

2.FR4 stiffener thickness: 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm~1.6mm

3.Stainless stiffener thickness: 0.1mm, 0.2mm

The disadvantages and advantages of FPC stiffener


Stiffener type advantages disadvantages
PI Small tolerance Not very hard
FR4 More thicker thinkness choice Bigger tolerance
Stainless Hard and stable Assembled by hand and hard to rework

You got it? If you have any comments, please kindly feel free to let me know. Please contact Best Technology at sales@bestfpc.com.

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What is the FPC tooling?

Recently, many customers asking me what is the flex PCB tooling included? And why we need to opening a tooling? How many types of tooling for flexible circuit? How to choose the suitable tooling for flex pcb?

Today, let’s learn about the Flex PCB tooling together. The FPC tooling is always used for cutting the FPC outline and coverlay. So it has included the FPC outline and coverlay tooling.

For samples production, normally we will open a tooling to save the cost and time for our customers, because the tooling will be scraped if you update the new version. So we will use the laser machine to cut outline and coverlay. But the productivity of laser cutting is longer than a tooling cutting the outline, that’s why we need to opening a tooling for volume production.

In generally, there are only four types of tooling in our production process.

1.Normal tooling, it is the most common used for most the flex pcb to cutting the coverlay and outline. The FPC appearance tolerance is 0.1mm, and the gold finger size tolerance range can be controlled at 0.15mm.

  1. Mediumn silking tooling: The precision is high, and the lifespan is better. The punching times is around 200,000 times. The punching effect appearance is good and smooth. The tolerance is 0.07mm. But the cost is high, and the tooling making time is longer than normal tooling
  2. Precision tooling: The surface is very smooth, it is usually used for tolerance very strict flex pcb. The gold finger tolerance can be controlled +/-0.05mm. But the cost will be also much higher than normal tooling.

4.Knife tooling: It is usually used for cutting the simple flex pcb, more than 500 mm length flex circuit board and adhesive. The tolerance is around +/-0.2mm.

Do you still have any questions about the flexible circuit board tooling? If yes, please feel free to contact Best Technology at sales@bestfpc.com. Looking forward to receiving your feedback.

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What is the difference between solder mask and coverlay?

Have you ever been have trouble in selecting the solder mask and coverlay when you are design a flex pcb? Solder mask and coverlay has the same basic function of insulating, do you know the difference between solder mask and coverlay? Is it possible to make the solder mask and coverlay overlap together for insulating? Do you think the flexible solder mask is the same as rigid printed circuit solder mask?

1)Design: Actually, coverlay is widely used for flexible printed circuit board. Because of most of flex pcb will need to add the PI/FR4 stiffener and EMI shield. But if there are BGA pads and dense solder mask opening area, limits the minimum size of openings and the minimum web of material then can be retained between adjacent openings. I would like to share a coverlay and solder mask overlap together FPCB with you. The coverlay is applied first and the solder mask second with a slight overlap onto the coverlay to prevent any gaps in the combined layer. This kind of design have much higher requirements for our production to ensure your functional and reliable design. Below picture is a coverlay and solder mask overlay together FPCB, hope you will be interested in.

If the coverlay opening is square, the minimum size for coverlay is 0.6mm, and space is 0.25mm. Otherwise you need to print solder mask. If the coverlay opening is round, the mimimum size for coverlay is 0.25mm, and space is 0.15mm. Otherwise you need to print solder mask. Because too small coverlay webs will be easily damaged or broken during manufacturing process, and the limited of adhesive may not allowed for a good lamination.  Coverlay openings may also exhibit a small amount of adhesive squeeze out into the openings. Then the resulting design rules for coverlay are significantly different than those for solder mask. Attached the coverlay square and round opening picture for your reference, please kindly check it.

2)Thickness: Below is the pure green solder mask flexi pcb picture, it do not need to add the stiffener for PCBA (SMT assembly), and there are no BGA area, why it choose to use the green solder mask instead of coverlay? The normal coverlay thickness is 27.5~50um. And the solder mask thickness is 8~12um. Due to the customers need the ultra thin flex pcb. Then we suggest the customer to use the solder mask instead of the coverlay.

3)Color: The most popular coverlay color is yellow, we usually prepared the yellow, white, black coverlay in stock. Solder mask is available in a wider range of colors: green, black, white, yellow, etc. Please kindly note that the flex pcb solder mask is quite different to rigid pcb. The flex pcb solder mask cost is much higher than FR4 PCB.Because the flexible circuit board solder mask the withstand bending and high temperature is better than Rigid FR4 PCB. But the coverlay and solder mask for flex price is the same for us.

If you have any comments, warmly welcome you to contact us. Once we received your news, we will reply to you immediately. Looking forward to receiving your inquiry.

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How much do you learn about the loose-leaf rigid flex PCB?

Have you seen loose-leaf (layered) rigid-flex PCB? One end of the multiple flexible boards is fixedly connected to the main rigid board, each flexible PCB will laminate to a fixed connection of rigid part.

Each flexible circuit has a free end, and each flex board can be bent freely, which improves the bending performance of the multilayer PCB. The flex parts can be respectively bent to the required angular positions so that the layered rigid PCB can be connected with components at different angles and different spatial positions.

loose-leaf (layered) rigid-flex PCB

Many FPC have a limited bending radius, flex thickness & width and amount of copper will affect flexibility and bend radius. The loose-leaf approach does allow going below the minimum recommended bend radius. Separating the layers into single flexible printed circuit board within the stack up allows the minimum bend radius to be calculated based on the thickness of the individual layers. But the length of each single flex circuit is made somewhat longer than the one below it, it allows room for all flex parts to bend without undue stress to itself or to the layer immediately adjacent to it.

Best Technology is mainly manufacture FPC board and flex-rigid PCB boards. Below is a ten layers flex rigid PCB with eight different golden fingers sample picture for your reference.

loose-leaf (layered) rigid-flex PCB
loose-leaf (layered) rigid-flex PCB stack up

If you are interested in this designs, please feel free to contact us to know more details at sales@bestfpc.com

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What are the differences between the Poyester (PET) and Polymide(PI) material?

The flex pcb raw material and stack up will decide the flex circuit quality. According to the market demand, there are three types of base raw material used for Flexible circuit board. Poyester(PET), adhesive Polymide (PI) and adhesiveless Polymide (PI) . Do you know the difference between the PET and PI material? If not, let us learn about it together now.

The advantages and disadvantages of Polyester(PET) and Polymide(PI).

Attached is a form for your reference, hope it will be helpful you. And you can choose the right raw material according the below form.

 Polyester(PET)Adhesive
Polymide
Adhesiveless
 Polymide
Flexibility (2mm radius)BadGoodBest
Tear strength800g500g500g
Strip strength in the air1050N/M1750N/M1225N/M
Eatching>=20%BESTBadGood
Working temperature85~16585~165105~200
ChipBadGoodBest

The advantages of PET material: Production process is less, price is cheaper, lead time is shorter.

The disadvantages of PET material: Polyester material can not pass through soldering flow. Then it can not be working in high temperature environment.

The advantages of polymide (PI): It’s easy to bend. Can work in high temperature.

The disadvantages of Polymide (PI): The price of raw material is much higher than Polymide.

Below picture is the single sided FFC, ENIG 3u’’, 10pin, 0.5mm pitch, and it is made of Poyester(PET) material

BFS17386-B

Below picture is a 1layer flex pcb, 4 mil PET material, print silver ink, carbon finishing mask, insulation( protective coating), carbon resistance less than 500 ohm.

BFS18205

Below picture is 1L FPC, it is made of adhesive polymide raw material. ENIG 1u’’, 1oz Cu, 1mil PI, 1mil coveraly, and the total thickness is 0.13mm+/-0.03mm.

BFS20032

It is a single sided FPC, ENIG 1u’’, 1/2ozCu, 1mil adhesiveless PI, 1/2mil coverlay.

BFS20209

If you have any questions or would like to learn more, warmly welcome you to contact us at sales@bestfpc.com

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What’s the difference between rigid-flex PCB and flex PCB with FR4 stiffener?

In the production of FPC, normally we need to add different stiffener to meet the total thickness or hardness, such as PI stiffener, FR4 stiffener and stainless steel stiffener. But the FR4 stiffener after laminated is very similar to the rigid-flex PCB, especially there are also have drilling holes in FR4 stiffener.

Do you know how to identify FR4 stiffener and rigid-flex PCB? Please refer to the below picture. On flex PCB, you can see there are many PTH holes, maybe these boards are need to insert connectors and connect it to other products. So they need the hardness in this area.

From the left sample, we added the FR4 materials on bottom side, there are also have vias on stiffener, but no copper in vias, so this is FR4 stiffener. It can only increase the hardness of flex. From the right sample, the green part are still FR4 materials, but we plated copper for all vias, so it’s a rigid-flex PCB.

FR4 stiffener VS Rigid-flex PCB

Rigid-flex board has many production processes, high production difficulty, low yield rate, so its price is relatively expensive and the production cycle is relatively long than flex PCB. If the FPC with FR4 stiffener can meet your requirements, then it would be a better choice for you.

If you have any other question about stiffener or rigid-flex PCB, please feel free to contact us at sales@bestfpc.com

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