Blog  /  Take You To 5 Common Flex PCB Soldering Technology

Take You To 5 Common Flex PCB Soldering Technology

The technology behind soldering and welding has advanced a lot over the last decade. But, there is room for further improvement. Soldering engineers still have to settle for outdated processes and techniques. The research behind new and innovative technologies is still incomplete.

Plastic welding has emerged to be more complicated than rigid welding. However, it comes with a set of benefits. Flex PCB soldering can give excellent results if you can conduct it properly. The problem is that the information available about flexible welding is not enough.

In this article, we want to introduce you to the advantages of flexible welding. We will also cover different operation techniques.


Soldering process

(Alt – Soldering process )


What is the difference between rigid and flexible welding?
PCBs or printed circuit boards come in two variations, rigid and flexible. The soldering technique you need to use for them is different. They have varying properties.

Rigid PCBs are reliable and flexible. You will not be able to bend it or manipulate its shape. You cannot make any changes to the board once it is ready. You will have to build your device, keeping the board in mind.

Flexible printed circuit boards will allow you to exercise more control. You can design your circuit in a way that fits the electronics or components you use. Flex boards come with a unique printed circuitry. The component arrangement benefits from the malleable base material.

When you apply soldering techniques to a flexible board, it is adjustable welding. It can prove to be advantageous for several reasons. A flexible printed circuit board does not need many interconnects. As a result, it has minor contact crimps, solder joints, and connectors. The chance of failure is not as high.

If you are more familiar with rigid welding, you will have to educate yourself. Flexible welding is not smooth. The following processes are useful for flex PCB soldering. They will allow you to complete your task with finesse and precision.


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1. Low-temperature solder paste in Flex PCB Soldering


Solder paste is a component required during the manufacturing of PCBs. It is necessary for both flexible and rigid printed circuit boards. It helps to attach the surface mount components to the pads located on the board. The components adhere to the board because of the sticky nature of the solder paste. Then they form a mechanical connection as the dough becomes warm and melts. This electrical connection is long-lasting.

Using low-temperature solder paste is now a well-known practice. It works well for surface mounts assembly. This technique is especially helpful when it comes to flexible boards. The meetings are unable to tolerate the high temperatures reached during lead-free soldering. There are many sensitive components on the board. They might suffer damage because of the high temperatures.

For flex PCB soldering, it is ideal that you keep the temperature of the solder paste low. When you are creating the board, use low-temperature solder paste. You will altogether avoid the risk of damage, and the flexible board will remain unchanged. All components will behave as they should. Soldering flex cable to PCB will be easy.

If you are using a tin-based soldering alloy with a high melting point, there is a solution. You can tweak the composition to lower its melting point by adding indium or bismuth. The key to perfect low-temperature soldering is finding the ideal material. Soldering flex PCB to cable will be more accessible then.


Printed Circuit Board with many electrical components.

(Printed Circuit Board with many electrical components.)


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2. Flash technology in Flex PCB Soldering


Flash technology is yet to become a mainstream welding process, but it is already in the works. The technology uses a high-power homogeneous xenon light flash—the light solders all the components on the board to copper tracks on flex foils. You should use a lead-free solder paste when conducting this process. Some people use foil substrates made with polyethylene terephthalate for this process. They will not suffer any damage because of the selectivity of light absorption.

The temperature increase is enough to create a soldering effect. However, it does not pose a danger to the functionality of the board. There have been studies of the microstructure of joints soldered with flash technology. They have revealed that the bonds rely on the photonic flash intensity. This method is reliable and will produce lasting relationships. The light forms the attachment in a non-invasive manner and does not leave any inconvenient effects.

The primary use of flash technology lies in attaching ultra-thin chips to aboard. It can connect any other small, surface-mount, flexible component to a circuit board. Ultra-thin chip bonding is going the extra mile in providing useful solutions. The world of silicon technology is witnessing a revolution. Flash technology is making the use of this technology easy. Ultra-thin chip technology might become more accessible.


Flex PCB soldering

(Alt- Flex PCB soldering)


3. Reflow soldering technology in Flex PCB Soldering


Reflow soldering is an easy soldering process. It performs well for flexible boards. The technique uses a solder paste to form temporary attachments. You can place the tiny electrical components and their contact pads in contact. Then, this assembly becomes permanent under the effect of controlled heat. The solder paste 'reflows' in the form of a molten liquid and creates durable joints in the process.

Reflow soldering makes it easy to solder different types of surface mount components. When you are making a flexible PCB board, you have to choose a suitable solder alloy. It should have a comfortable eutectic temperature. When the fusion changes into a molten state, it shows properties of adhesion.


an infrared, convention, and hot air


There are many types of reflow methods that you can use- infrared, convention, and hot air. Isolated reflow techniques are ideal for soldering iron components. Since flexible circuits usually need extra fixturing and support, the method works well. You can vary the process parameters. Take the material limitations and thermal mass into account. This method is effective and time-efficient for soldering flex cable to PCB.

Semi-automatic welding requires you to conduct manual welding. However, you can use equipment that can control the welding conditions. As a welder, you can manipulate your welding gun and attain precision. This process is useful for flexible welding and flexes PCB soldering. If you want to go one step further, you can opt for automated welding. It will require minimal human observation.

There is no scope for manual adjustments and equipment controls. All you have to do is check if the machines are working as they should. An automated system reduces any chance of damage during flexible welding.


Technical process for soldering and assembling chip components on PCB boards, automatic soldering machines

(Technical process for soldering and assembling chip components on PCB boards, automatic soldering machines)


4. Flux Selection in Flex PCB Soldering


You cannot complete a soldering project without flux if you want good results. If you do not use a flux, there is a high chance that the work you put in might prove to be futile. You can spread the flux on the soldered metal. It will keep the surface tidy and clean until the molten solder alloy makes it way there. The fusion then tries to form the attachments. The flux also plays a vital role in helping the solder cover the surface area of the metal. For a flexible board, you have to be careful about the application of the flux. Using a flux pen will allow you to have complete control as you lay down the flux.


Solder flux


Solder flux can eliminate oxides and different kinds of impurities from the board. It can accelerate wetting during reflow soldering. There are different kinds of flux available on the market. It would help if you opted for the least acidic flux that you think will combat the oxides of your components. The typical fluxes are rosin flux, organic acid flux, and inorganic acid flux.

Organic acid fluxes work better than rosin acids and can remove oxides much faster. Inorganic acid flux is ideal when you are working with durable metals like copper and brass. Choose your flux based on the components you are using on the flexible board.


Flux selection and PCB soldering(Alt – Flux selection and PCB soldering )


5. Hot-press Welding Technology


Hot-pressure-welding will allow you to form bonds between the components and the board. You have to use heat and pressure only. You will not need a filler metal to conduct this type of welding. You have to apply heat to both the surfaces to attach them by using pressure. The flame produced by oxyfuel torches is adequate as a heat source.

It will also allow for preciseness during application. When the two surfaces attain the correct temperature, you have to remove the heat source. When there are no obstacles, and you can bring the bodies closer and attach them under pressure—the open joint process.
In some instances, the surfaces can already touch under pressure when you apply the heat, The closed joint process. When using this method on a flexible board, make sure you choose the correct material. It should have forge ability properties to accommodate the new fixture. It will help make flex PCB soldering easier.


Hot metal billet under the news

(Hot metal billet under the news.)




After reading the article, I believe you have obtained the underlying technology of flexible PCB welding. If you have any questions, you can also contact us in time. We will provide you with compliant custom PCBs to help you produce PCBs faster and better. We support high-volume and low-volume orders. Contact us today for more details. OurPCB allows you to solder flexible boards to your PCB easily!



Special Offer: Get $100 off your order!

Claim your $100 discount by sending an inquiry today. Act now to save on your next project!
Please email [email protected] for details.