How to Paste Coverlay on FPC?

If you have ever learned something about flex circuits, you would know there is a layer of coverlay on it. Pasting coverlay on flexible circuit is to prevent it from the damages of dust, moisture and so on. Meanwhile, it also plays an role in insulation. We have learned something about the benefits of pasting coverlay on flex circuits, but how to paste the coverlay? Let’s take a look.
To begin with, we need to prepare the coverlay material, checking whether the soldering iron has power, cleaning the residue of soldering iron and the dust-free paper.

The procedures of pasting the coverlay on FPC:

  1. Checking whether the coverlay and film have problems, including missing punching, missing drilling, too large burr on the coverlay etc.. After that, clean the dust on the surface of coverlay with packaging cleaner.
  2. Cleaning the worktable and putting the coverlay, soldering iron and other tools in the right place.
  3. Checking whether there are oxidization, litter, dust etc. on the flex circuits to be pasted.
  4. Pasting the coverlay should follow the requirements of process and the MI data. It should be strictly follow the “C”marking line, pad or counterpoint hole when align.
  5. How to peel the coverlay off: putting the covelay on the optical desk, but please remember that the release film is facing up and the coverlay is facing down. After that, holding the coverlay then peeling off the release film slowly.
peeling the coverlay off

peeling the coverlay off

  1. Fixing the coverlay on FPCwith soldering iron after the coverlay is aligned with the “C” marking line of the flex circuit board and ensure it is correct, so that the coverlay can not deviate or peel off. However, please remember the soldering iron can not burn the products.
pasting coverlay on FPC

pasting coverlay on FPC

  1. Single-side lamination: after pasted the coverlay on FPC, it should be gone through the machine with temperature between 160°C-165°C. Next, until the board got cold, the release film should be peel off and carry out the single-side lamination and self-checking.

Notices:
1. It is necessary to wear rubber gloves to prevent the flexible printed circuit board from oxidization or dirty.

  1. It must be kept clean during pasting coverlay on FPCto prevent there are dirty residues on flex circuits.
  2. It is required to check whether the coverlay is broken, wrinkled, scratched, etc..
  3. Do not wear accessories to avoid scratching the board.
  4. It is necessary to confirm that the coverlay leave a little bit space for plating if the flex circuitsare tin or gold plating.
  5. The hand could not beyond the handle to avoid burning when holding the soldering iron.

Best Technology is the premier expert in the manufacture of electronic components, brings a unique combination of technology and quality that offers a competitive supply of flex circuits and rigid-flex circuits and other flexible circuit products. With high qualified engineers, we are able to help you find a FPC with high quality. To find out more, contact Best Technology at 0755-29091601 or check the website: https://www.bestfpc.com

Meeting Customer from UK

On November 29, 2018, we are pleased to host Caroline O’Brien from UK during her trip in China. Both of us have a really friendly and nice talk in the meeting room of Best Technology.

During the meeting, we introduced something information of our company firstly. Then the detail information of flex circuits in the sample album also explained in details by our account manager Celine. After that, the customer recognized the comprehensive strength of our company.

Celine introduced FPC

Celine introduced FPC

After the short meeting, Caroline went to visit our FPC factory in the company of our general manager Peter. The manufacturing process of flexible circuits that customer  interested in are explained clearly by Celine. Caroline was satisfied with our equipments of production line with high performance and high quality.

Visited FPC factory

Visited FPC factory

After the visit, Caroline knew Best Technology in further. In the future, we hope we can make it better and provide the most suitable and the most satisfying service for our clients, too.

Took a photo at Best

Took a photo at Best

Since throwing its hat into flex circuits manufacturing industry, Best Technology is always dedicated to be customers’ best partner of flex circuits and rigid-flex circuits in China, to serve worldwide customers.

The structure, technique and design of FPC (2)

1. The structure of FPC:

 According to the layer of conductive copper, FPC is divided into single layer, double layer, multilayer, dual access, etc.

 The structure of single layer: the most simple. Base material + transparent adhesive + copper is one set of the raw material; coverlay + adhesive is another. Firstly, the copper needs to be etched to get the traces, while the coverlay needs to be drilled to expose corresponding soldering pad. After cleansing treatment two set of raw material are bonding together by rolling. Immersion gold or tin is done on the exposed soldering pads to protect from oxidization. At last, FPC is punched into smaller ones of corresponding shape.

 Some FPC doesn’t use coverlay but prints solder mask on the copper directly, which lowers the cost, but worsens the mechanical strength of FPC. Using coverlay is the best, unless at the occasion of low mechanical strength and the lower price the better,

 The structure of double layer FPC: when the circuits are too complicated, the single layer FPC can’t or needs copper to do ground shield, double layer even multilayer FPC is needed.

 The most typical difference between multilayer and single layer FPC is that the multilayer FPC is added with through-hole structure to connect the copper on every layer. The first workmanship of base material + transparent adhesive + copper is to make through holes. Holes are drilled o the base material and copper, after cleansing treatment they are plated with a certain thickness of Cu, then the through hole is done. We call it PTH (plated through hole). The technique after is almost the same with single layer FPC.

 The structure of dual access FPC: dual access FPC has soldering pads on its two sides, mainly used to connect with other circuit boards. Although it has similar structure with single layer FPC, its technique has great difference. Its raw material is base material + adhesive + copper, coverlay + adhesive. Holes are drilled on the coverlay according to soldering pads location, then stuck on the copper. After etching the soldering pads and traces another coverlay with drilled holes is stuck on that.

 2. The performance and selecting method of the materials

 (1) Base material:

 PI (Polyimide) is the most common used, which is a kind of macromolecule material of high temperature proof and high strength, invented by Dupont. The polyimide made by Dupont is called Kapton. Besides some polyimide made in Japan can also be found. Its price is much lower.

 Polyimide can bear 10 seconds of high temperature of 400 degree centigrade. Its tensile strength is 15,000~30,000 PSI.

 The base material with 25um thickness is the cheapest and the most popular one. If we need the circuit board to be more rigid, we should choose 50um. Otherwise, if we need the circuit boards to be more flexible, then choose 13um.

 (2) Adhesive:

 It is divided into epoxy resin and polyethylene, they are all thermosetting adhesive. The polyethylene’s strength is lower. If we hope the circuit boards to be more flexible, then choose polyethylene. The thicker the base material and the adhesive on it is , the more rigid the circuit boards are. If the circuit boards have to be bent in a large area, we should choose thinner base material and adhesive so as to reduce the stress on the surface of the copper, then lower appearance of micro crack.

 (3) Copper:

It is divided into rolled annealed copper foil and electrodeposited cooper foil. Rolled annealed copper foil is of high strength and can stand bending, but its price is higher. Electrodeposited copper foil is much cheaper, but of low strength, easier to be bent.

When we choose to use rolled annealed copper foil, we should pay attention to the direction of the copper. The direction of the copper has to be the same with the bending direction of the circuit boards.

 (4) Coverlay and its adhesive:

 25um coverlay would make the circuit board more rigid, but it is cheaper. Therefore to the circuit board needing to be bent greatly, we’d better choose 13um coverlay.

 The adhesive is also divided into epoxy resin and polyethylene. The FPC using epoxy is more rigid. After thermosetting, there are some adhesive squeezed out at the edge of the coverlay. If the soldering pads are larger than the hole on the coverlay, the adhesive squeeze out would reduce the size of the soldering pads and lead to irregular edge. Therefore, we’d better choose 13um adhesive.