What Are The Steps To Manufacture A Rigid-flex PCB?

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In this article, we will be discussing all the steps needed for the manufacture of high-power rigid-flex Printed Circuit boards. But before diving into steps, we should understand what exactly rigid-flex PCB is.

What is Rigid-Flex PCB?

Hybrid PCB

Rigid-flex PCB is a hybrid Printed Circuit Board that has qualities of both flexible as well as hardboard. This is a very unique and special type of PCB manufacturing in which flexible circuit components are joined with a rigid board either externally or internally.

Multi-layered board

This rigid-flex PCB is a multi-layered board in which a flexible layer is internal to the hard layer. This type of PCB manufacturing provides an all-in-one circuit with the best result and good performance.

3D designing

Rigid-flex PCB is a bit difficult to design and manufacture because it calls for 3D space, which also offers great spatial efficiency. This allows designers for 3-dimensional designing, and they can easily roll, turn and fold the board to give their desired shape.

So, if you are a tech person and love to know about PCB manufacturing, then you are in the right place. Paragraphs below will explain all the steps involved in Rigid-flex PCB manufacturing in detail.

PCB

Steps involved in rigid-flex PCB manufacturing

  • Pre-cleaning of material

It is the first and foremost step in rigid-flex PCB manufacturing. PCB is made up of Copper laminate, which acts as a base material for its manufacturing. Therefore cleaning of copper is necessary to make it resistant. This pre-cleaning will help in depositing other layers over copper laminate.

Mostly Copper laminate contains an oxide layer on its surface to make it antioxidant and protect its surface. Two different cleaning processes remove this oxide layer.

  • Mechanical cleaning

Mechanical cleaning can be done with the help of scrubs or by spraying any abrasive material. These scrubs manually remove the oxide layer from Copper laminates.

This mechanical cleaning not only removes protective layers but also provides roughness to copper laminate which will help to provide a good base to rigid-flex PCB. Abrasive spraying can remove up to 2 micrometers of copper.

  • Chemical cleaning

Chemical cleaning consists of 3 steps

  • Firstly immerse the copper into an acid solution or fed it to acid spray
  • Then, treat copper laminate with sodium persulfate solution to micro etch it.
  • Now cover the copper laminate with any good oxidized agent that will prevent oxidation and adhesion of copper.
  • Formulation of the circuit pattern

The second step in rigid-flex PCB manufacturing is the generation of circuit patterns. This step is very important as it gives the base to the printed circuit board. Generally, two methods are used for this purpose.

  • Screen printing 

It is an ancient process of creating circuit patterns. This method is also known as silkscreen printing. It can be done by hand or by any machine. Both processes are the same; the difference only lies in the type of inks used.

Screen printing is mostly used when less amount of work is required. It is a very popular and widely used method because it can print on any surface, either fiber, plastic, paper, or leather.

It involves creating a stencil on a mesh silkscreen and then pushing ink to impart design on the surface below. It directly produces the desired pattern without any extra effort. The thickness of the pattern produced by screen printing can not be greater than 4 to 5 microns.

  •   Photoimaging

Although photo imaging is a very old process of printing circuits but is equally popular nowadays. In this technique, a dry photoresist film comprising of the required circuit pattern is placed near the copper laminate.

 Then the entire setup is exposed to UV light. This will help in the transfer of the entire pattern from photoresist film onto laminate. Now you can use any chemical to remove the film from the laminate.

By considering any of the above two processes, you can easily generate circuit patterns.

  • Etching of Copper laminate

Etching means the removal of extra copper from copper laminate. It is a very tricky step in rigid-flex PCB manufacturing. This step leaves only traces of copper that are required to perform functions.

Etching can be of two types.

  •  Wet Etching

In wet etching, the copper laminate is treated with any specific chemical that results in a chemical reaction that dissolves unwanted copper. This type of etching depends on the selection of chemical etch material.

PCB

Chemicals can be acid or base.

  •  Acid

Acid such as ferric chloride or cupric chloride can be used.

  1.  Base

Base like a mixture of hydrogen peroxide and water can be used. Etching by using a base is more powerful than acidic etching and gives better results.

  •  Dry Etching

Dry etching is also known as plasma etching. This type of etching plasma initiates a chemical reaction between base and surface atoms of copper laminate. This reaction results in the removal of extra copper. When all unwanted copper has dissolved, this point is known as the breakout point.

  • Drilling holes in Rigid-flex PCB

After successfully engraving both sides of copper laminate, it is all set for the drilling process. According to your client's requirements, you can drill holes, vias, and pads.

Drilling machines are available in all forms according to the size of the hole. They vary from high-speed drilling machines to laser drilling machines. Laser drilling machines are mostly used for making ultra-small holes.

Being a PCB manufacturer, you must know the use of appropriate drilling machines to achieve desired results. Generally, Carbon dioxide and Excimer YAG laser are used for drilling medium to small holes rigid-flex PCB.

  • Through-Hole plating

Through-hole plating is one of the most difficult steps in rigid-flex PCB manufacturing. It requires a great deal of care and precision.

Through-hole plating is done to easily use both sides of plates and connect other layers to them. The plating is of copper as copper is a conductor, so it allows electrical conductivity to travel throughout the board.

Through-hole, plating is similar to testimony in rigid-flex. This type of plating recommends thickness not greater than one million miles. It has many advantages like ease for prototyping, strong physical connections, heat tolerance, and power handling capabilities.

  • Protection of Rigid-flex PCB with cover lay or cover board

Rigid-flex PCB is mostly covered with cover-lay or cover -board. Both sides of PCB are covered to protect it from harsh effects of the environment, heat, and solvents.

A cover board is a simple board that is easily placed over the substrate while cover lay is not placed directly. For cover-lay, PCB manufacturers mostly use polyimide and an adhesive. Cover lay is imprinted on laminate with the help of screen printing and by using UV light. For proper grip of the cover, lay heat and pressure limits are considered.

Selection of cover-lay and cover board mostly depend on available materials and PCB manufacturing methods.

  • Cutting of Rigid-flex PCB

Cutting of rigid-flex PCB is a very crucial step and needs much caution. Most PCB manufacturers select hydraulic punching and die set methods for rigid-flex PCB manufacturing. These processes are usually used for mass production of PCB and on a higher scale.

 Small-scale manufacturers should go for any other alternative as these processes are heavy on pocket. One of these alternatives is the use of a blanking knife—this is a long razor blade, which made the Rigid-flex circuit shape. After shaping, it attaches to the routed hole in the supporting board.

  • Electrical tests

Electrical tests are performed to ensure that the circuit boards are error-free and can work properly with electricity.

There is no specific electrical test for Rigid-flex PCB, some general tests are performed to evaluate its performance.

Stringent electrical testing

This type of test is performed to check the isolation, continuity, quality, and performance according to design specifications.

Capacitance testing

This type of testing looks for shorts in the board.

Resistance testing

This type of testing is used to measure resistance in ohms. For a good rigid-flex PCB, its resistance should be less, which indicates that it is a good conductor.

  • Verification of final product

This is the last step in the manufacture of rigid-flex PCB. It accounts for all the possible parameters to check before working on PCB. Material properties mostly assist you in the verification of PCB. For automotive use, we must look for moisture, heat, shock, and chemical properties.

The real material properties govern the least permitted bending radius and the product’s safety.

Conclusion:

This article has thrown light on all the steps of rigid-flex manufacturing in detail. The steps mostly begin with plans or design and then all the in-between processes, which ends with different kinds of inspections like electrical tests, chemical analysis, tolerance, etc.

This article will help you in selecting the best PCB manufacturer or PCB designer by keeping in mind all the aspects related to its manufacture.

Rigid-flex PCB manufacturing requires a great deal of caution and a good team of PCB engineers that pay attention to every minor detail regarding manufacture as its not a child’s play to design PCB that controls all functions of your smartphone, PC, laptop, aerospace engine, and else everything related to electricity.

We hope this article will help you in getting your rigid-flex PCB manufactured by a team of experts and experienced engineers.

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