Electronic Design - Discuss in detail the design specification of soft and hard board and flexible circuit board

Discuss in detail the design specification of soft and hard board and flexible circuit board

PCB rigid-flex board manufacturers: There are many people who did not know before, because their concept should not use this technology.

However, more and more developers are facing increasing pressure from the construction of high-density electronic devices.

In addition, their headache is that they must continue to reduce their costs and manufacturing time.

In fact, this is really not a new technical problem.

Many engineers and developers have had headaches for a long time and are facing increasing pressure.

Therefore, it is wise to use flexible, flexible and flexible connector cards.

Therefore, we can easily discover the dangers hidden by design errors and prevent these errors in the future.

Now, we need to know what basic materials are needed to make these boards. Materials for flexible circuit boards Protective films and protective films First, considering the usual rigid printed circuit boards, the base material is usually glass fiber and epoxy resin.

In fact, these materials are a kind of fiber, although we call it "stiff", if you take off one layer, you can feel its elasticity.

This may make the board harder due to the cured epoxy. Because it is not flexible enough, it cannot be applied to certain products. However, this also applies to many simple electronic products whose maps are uninterrupted.

In more applications, we need a plastic film that is more flexible than epoxy resin. The most commonly used material is polyimide (PI), which is very flexible and strong. We cannot tear or enlarge it easily.

In addition, it has amazing thermal stability and can easily withstand temperature changes during fusion welding. In temperature fluctuations, it is difficult for us to find its deformation.

The polyester (PET) is another fluent flexible circuit material.

Compared with the polyimide film, the heat resistance and temperature deformation of the polyimide are higher than the heat resistance of PI.

This material is commonly used in low-cost electronic devices where the printed circuit is enclosed in a flexible film.

Because PET cannot withstand high temperatures, let alone soldering, flexible printed circuits are usually manufactured by cold pressing. I still remember that this kind of flexible connection circuit is used in the display part of the alarm clock, making the radio frequency often abnormal, mainly due to poor quality connectors.

There are a variety of exploration materials available, but they are rarely used.

PI, PET, particulate epoxy resin and glass fiber are common materials used in flexible circuits. In addition, the circuit must also use another protective film, usually a PI or PET film, and sometimes use anti-mask soldering ink.

The protective film, like the protective circuit of the welding layer, can insulate the wire and protect it from corrosion and damage. What are the different thicknesses of PI and PET films? Three? Mil, the thickness of one or two minutes is fluent. Glass fiber and epoxy resin have a larger thickness, usually 2 to 4 cubic meters.

Printed yarn, usually carbon film or silver ink, is used in the above-mentioned economically priced electronic products, but copper yarn is still a common choice.

According to different applications, we must choose different copper foils.

If you want to replace yarns and connectors, thereby reducing time and manufacturing costs, electrolytic copper foil is the best choice for adaptive printed circuit boards.

The electrolytic copper foil can also be used to increase the weight of copper to increase the current carrying capacity, so as to obtain the width of the copper foil such as planar inductors.

As we all know, copper is relatively poor in work and stress fatigue. If the flexible circuit must be repeated or repeated during the final application, a high-quality immersion copper (RA) is a better choice.

Of course, a larger roller will increase the cost, but before fatigue cracking, the rolling of the quenched copper foil can be folded and folded several times.

This will increase flexibility in the Z direction, and we need this.

In various applications, this will make us live longer.

Since the blade process extends the structure of the seed in the planned direction.

On the Blu-Ray machine, the flexible circuit application is connected to the laser and the main printed circuit board.

Please note that the flexible circuit on the circuit board on the laser head must be folded at a right angle to the right.

Here, a rubber ball is used to improve the connection of the flexible circuit.

Adhesives Generally, we need adhesives to bond copper foil and film (or other films), because unlike traditional FR-4 boards, there are not many flavors on the surface, and it is impossible to bond under high temperature and high pressure. Contact under high temperature and high pressure.

The manufacturer provides corrosive rolling for corrosive copper foil on both sides and on both sides. It uses acrylic and epoxy adhesives, and the thickness is the thickness.

The mill or mile this adhesive is used exclusively for flexible printed circuits.

Due to the introduction of new processing techniques, such as direct coating and deposition of copper foil on Pi, "non-stick" laminates are becoming more common. In HDI circuits, a larger interval and smaller holes are required, and these films can be widely used.

Silicone resins, hot melt adhesives or epoxy resins are used to add protective pearls to hard and hard joints.

This will enhance the mechanical strength of the hard joint and ensure that fatigue or tearing does not occur during repeated use.

Summary of content It is important to fully understand the materials used in hard copy or hard printed circuit boards.

We can also give the manufacturer the freedom to choose materials according to the application, but this will pose a hidden danger to the failure of the final product.

Understanding the properties of materials can also help us design, evaluate and test the mechanical parts of our products. If research and development of automotive products are carried out, it is necessary to carefully simulate heat dissipation, humidity, chemical corrosion, impact, etc., in order to be able to use appropriate materials to achieve high reliability and minimum product radius.

Ironically, he often encounters difficult environments, so let us choose the last flexible model to apply hard and soft composite panels.

For example, low-cost, low-cost public electronic devices are often affected by vibration, low prices, sweat, and other issues.

The structure of the flexible board

At first glance, the combination of a typical flexible card or a set of soft flexible boards looks very simple.

However, some additional steps are required to produce these products. The manufacture of any type of hard via board starts with the manufacture of one or two-sided flexible boards.

Copper foil. The lamination process requires the application of a fine adhesive layer on the film, while the glueless process requires copper plating on the film. Vapor phase deposition (such as cathodic sputtering) is often used to sow "seeds" so that nodules can condense during subsequent chemical precipitation.

Then, the drilling, plating and etching process of one or both surfaces of the flexible board is similar to that of a general rigid board on both sides.

Manufacturing process of flexible board

The next GIF animation shows the process of manufacturing a flexible printed circuit board on two typical sides.

1. Application of adhesives or seeds The use of epoxy resins, acrylic adhesives or sputter coatings is the key to making thin copper coatings.

2. Add copper foil Press RA/ED on the adhesive (this is the inertial method) or use the autocatalytic deposition method.

3. Drilling Passes and holes are usually mechanical. Multiple flexible boards can be performed simultaneously by working on a rotating plateau. Using the same method as the rigid board, the pre-cutting of the flexible board can be combined with drilling, which requires more detailed records, but can reduce the accuracy of alignment. Generally speaking, laser drilling is used to handle very small drilling, which greatly increases the cost because each movie must be drilled separately. Shell (ultraviolet) or YAG (infrared) for the treatment of microorganisms, for drilling CO2 lasers with medium apertures (above 4 meters). Both large holes and scissors can be processed by punching, but this is another step.

4. Penetrating flat plate After the drilling is completed, copper will be added to the hole by the same deposition and electroplating method as the hard plating.

5. Etching ink The surface of the film covers the photoresistor and is exposed in the desired pattern to eliminate undesirable resist before chemical copper attack.

6. Etching and painting After the exposed copper foil is attacked, the chemical corrosion resistance is discovered.

7. Cover film The top and bottom of the flexible board are protected by cutting film. Sometimes, the flexible card should be welded to certain components, so the coating film functions as a weld-resistant layer.

The most common coating material is polyimide, which is associated with an adhesive. The present invention can also use non-adhesive methods. In the process without glue, apply the photosensitive flow to the flexible card, which is the same process as the rigid card. In order to reduce costs, ultraviolet radiation can be used to use silk screens.