What Is The Process Of Multilayer PCB Fabrication?

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PCBs have been there for a long time now, but the newer versions are coming out. First, PCBs became small in size, and there came a time when that size could not be further decreased. It was one of the deriving reasons behind the making of multilayer PCB. Multilayer PCB is a wonder of technology that helps us put huge circuits in tiny places.

What is multilayer PCB?

The name here is pretty much self-explanatory. The multilayer PCB is a PCB that is made after joining two or more layers of PCB to each other like a sandwich. There are many examples of things that currently use multilayer PCB, but the most common ones are modern-day mobile phones and Tablets.

 PCB manufacturing

Step By Step Process of multilayer PCB fabrication.

While the process of multilayer PCB manufacturing is almost the same, there are a few necessary additional steps. So, here we have the step-by-step process of multilayer PCB manufacturing.

Front-end engineering is the first step that is mostly related to the designing of PCB.

The first step in multilayer PCB manufacturing is designing and engineering the PCB. Every PCB has its different functionality and working, so a different engineering process is needed. However, one thing that goes the same for all PCBs here is planning to layout the design of connections between points for efficiently creating the PCB. This process includes a lot of:

  • Planning
  • Designing
  • Editing
  • Prototyping
  • Penalization

After repetitive tries, the best PCB prototype is formed that is carried out for the next processes.

Once the designing process is complete, the process moves to the photo plotting phase.

The next process in multilayer PCB manufacturing is photo plotting. It is the part where a laser photoplotter is used to plot the images directly on the dry film of the PCB. It makes the process a little more accurate and reduces the cost and time for manufacturing the PCB. This process step is done differently for different layers of the multilayer PCB.

The next part of the process is imaging, developing, etching, and stripping.

Now that the image plotting is done, the next part is about imaging and developing. The initial design needs traces, pads, and metal grounds on the PCB that are all done in this phase. After imaging and developing, etching and stripping are done to prepare the PCB surface for the copper plating process by following a specific pattern.

After this process completes, the PCB is left with conductive copper patterns. This copper pattern is for the inner layers for PCB and not for the outer layers.

Now the multilayer PCB goes for optical inspection that is completely automated.

It is highly important to inspect things at this phase to ensure that the next steps start with everything right. So, the PCB goes through the automatic optical inspection machinery that takes the images of the PCB and checks them against the data provided. It points out any missing copper connections, shorts, over or under etching, or other issues.

In this way, identifying problems saves from facing any problems in the further parts of the process.

Oxide chemical treatment to prepare PCB for the lamination process

Now that all the layers have passed through the optical inspection step, the next step is about treating the layers to stick together in the coming phases. This chemical treatment increases the roughness of the copper contact pads for better bonding between layers.

By performing this step, the multilayer PCB manufacturing process makes sure that all the layers of multilayer PCB stick together very well.

Lamination of the PCB to join multiple layers together

Lamination is the next part in the process of multilayer PCB manufacturing that joins the conductive and nonconductive parts together through the lamination process. High temperature and pressure are used along with hydraulic press so that the layers melt and then join together.

Drilling through PCB to get all the required holes on the PCB surface

Drilling is an important part of the whole manufacturing process because not all the components are soldered on the surface. Some need to pass through the holes and then are soldered. Moreover, there is a need to mound the PCB somewhere in the device that they are being made for. So, the PCBs are drilled for different holes on different surfaces for all of these needs.

All of the drilling processes are done through proper data that is submitted to CNC machines.

Copper deposition to make PCB conductive

The next part of the manufacturing process is to deposit a thin layer of copper. This is done on the exposed layers of the PCB, and the copper is deposited on all parts of the exposed PCB layer, including the holes that were just freshly drilled. A special electroplating process is used to make sure that a thin layer of conductive copper is left on the fiberglass surface.

Photoresist outer layer formation to prepare PCB for electroplating

Now the PCB needs to be prepared for electroplating, and for that, it is necessary to apply the outer layer images. So, first, the outer layer is coated with a photoresist with the help of the laminator machines. Then the photoresist is exposed to direct imaging techniques using lasers. In this way, a conductive pattern is exposed that can be plated with copper in the next step.

Electroplating for plating copper layer on the PCB surface

In this step, the PCB surface goes through electroplating techniques. So, copper is plated on the conductive pattern of the PCB. The electroplating technique makes things so simple and easy here.

However, a tin plating bath is also ensured for depositing a layer of tin on copper. This serves as protection for the copper patterns when the PCB goes through the etching and stripping processes.

Stripping and etching to remove the additional copper from PCB

This step itself is known as a whole SES process, so the panel is stripped, and the copper gets exposed along with the photoresist remains. This is done to expose the parts that will be involved in the soldering process. As this step completes, all the electrical circuit-making work is complete. The next steps in the process will only be about preparing the PCB for usage.

Solder masking makes sure that only the soldering terminals are left bare

At this point, the copper points and patterns are bare, which means that there are major chances of all sorts of short circuits. So, the solder masking technique is used so that there is no chance of any solder bridging or short circuits. In this step, an epoxy-based resist is applied on the surface of the PCB that is also photosensitive.

The screen printing process makes sure that the whole PCB panel is completely covered. UV light is used to treat and cure this layer. After this step completes, the PCB is baked in the oven so that the solder mask layer cures and hardens to protect the copper patterns.

Applying the surface finish to protect everything from heat

Although the copper circuits are secure against short circuits, they are not secure against heat that will come when soldering components on the PCB. So, it is also important to protect the whole PCB surface against heat. In this step, a surface finish is applied to cover the exposed copper sections on the PCB.

This surface finish also prevents those copper points from oxidation because otherwise, it will become useless for soldering. Hence, the PCB becomes safe against heat as well as oxidation.

Automated circuit testing ensures that there are no issues in the circuits created

Now everything related to making the PCBs is completed, and the last part of the process before PCB gets its final shape is testing. Thorough testing ensures that there are no issues in the final circuits. Automatic machines with flying probe testers are used in this step to ensure that all the circuitry and points are made right according to the requirements, and there are no defects.

Fabrication gives every PCB its final shape.

Up till now, the PCB is present in the form of a huge panel. Each panel has a lot of individual PCBs that need to be separated. For this part, the panels go through the CBC machine that fulfills all the fabrication needs. CNC cuts and trims each PCB into its desired shape and size using different router bits.

Inspection to ensure that every PCB is well according to the standards

Now we have what you can call an individual PCB. To make sure that this final product is good in terms of visuals as well as performing, these are reviewed. An inspector starts by reviewing the documentation and then checks the PCB.

It is made sure that every unit is well done according to the customer's requirements. After this checking, the multilaminate PCB manufacturing process finishes.

Final Thoughts:

Multilayer PCB manufacturing is not as simple as it seems, but most of the steps are similar to simple PCB manufacturing. However, the steps that are only a little different or additional help us achieve this wonder of technological advancement and development. We hope that now you know all about the multilayer PCB manufacturing process.

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