Circuit boards before assembling the electronic components are referred to as printed circuit board (PCB). Immediately you solder the electronic components, the board becomes Printed Circuit Assembly, PCB Assembly, or Printed Circuit Board Assembly. There are different automatic or manual PCB tools for assembly in the whole process.
Note that printed circuit board assembly – pcba design is different from the process involved in PCB manufacturing. Manufacturing PCBs deals with different processes, which includes the designing of the PCB and the creation of the PCB prototype. Immediately the PCB is set, there’s a need to solder Passive and Active Electronic Components before it is usable in any gadget or electronic equipment. This electronic components assembly depends on the Printed Circuit Board type, the circuit board’s purpose, and the electronic component type.
PCBA Design: Introduction
Electronics are viewed as a very important aspect of daily living. Everything, including our cars and smartphones requires electronic components. Making the core of these electronics is knows as PCB – printed circuit board.
Most people know PCBs anytime they see them. If you are not sure, they are green chips that are covered in copper parts and lines, which you can find at the core of electronic devices. Also, they are made with copper lines, fiberglass, as well as other metal parts. The boards are held tightly held with epoxy. Also, the insulation is made with solder mask. Its green color can be found in the solder mask.
However, have these boards been observed with these components well stuck on? Don’t you ever see them as simple PCB board decorations. Circuit boards that are advanced will never perform it functions until you mount the components on it. PCBs with mounted components are referred to as assembled PCBs.
The whole process involved in the manufacturing is PCBA or PCB assembly. Those copper lines, which are seen on the bare board, are called traces. These boards link components and connectors electrically to each other. These signals are run between those features, permitting the functioning of the circuit board in a specially designed pattern. They perform simple and complex functions and still PCB size can be smaller compared to a thumbnail.
Now, the question is, how do these devices come to be? The pcba design and process is a straightforward one. This consists of some manual and automated steps. With all the steps involved in the process, the manufacturer of the board possesses both automated and manual options to choose from. In order to comprehend the Pcba design process properly, we have taken time to explain the steps comprehensively.
PCBA Design Basics
The pcba design process usually begins with the printed circuit board’s most important and basic units. These basic units include the base, which is made up of some layers, with each of these layers playing a significant role in the final PCB’s functionality. These layers include:
The Substrate
This is a PCB’s base material. This is what gives rigidity to the PCB.
Copper
To each of the PCB’s functional side, a thin layer of copper foil, which is conductive, is added. If the PCB is a single-sided one, then it stays on one side, but if it is a double sided one, then it is added to both sides. This is also regarded as the copper traces layer.
Solder Mask
You will find the solder mask on the copper layer top. This is what gives the green color to the PCB. It prevents the copper traces unintentionally from coming in contact with other conducting materials. What we mean is that, the solder ensures that everything is in place. The solder mask’s holes are areas where you apply the solder to fix the components to the circuit board. The solder mask is one very important step for the smooth pcba design and manufacturing. This is because it prevents the soldering step from taking place on parts that are unwanted.
Silkscreen:
A PCB board’s final layer is the white silkscreen. Labels are added to the printed circuit board by this layer. These are in the form of symbols and characters. They also indicate each board component’s function.
Across all printed circuit boards, these components and materials are usually the same for most cases. However, the substrate is an exception. The PCB’s substrate material usually changes according to some qualities like bendabability and cost. This is what all designers are searching to see in their completed product.
Types of PCBs
PCBs are of three major types
Flexible PCB: This type of PCB provides more pliability compared to their counterparts that are more rigid. These PCBs materials are usually bendable and are plastics with high temperature like Kapton.
Rigid PCB: Majority of PCBAs are rigid PCBs. They are the most common. The rigid PCBs solid core gives thickness and rigidity to the board. These PCB bases that are inflexible are made up of a few materials. One of the most frequently used is fiberglass, which is also called “FR4”. PCBs that are less expensive are manufactured with materials such as phenolics or epoxies. Although, these are not as durable as the FR4.
Metal Core PCB: This is another option instead of the FR4 board. These boards, which are manufactured using metal core, tend to efficiently spread heat compared to others. This helps in dissipating heat. They also help in protecting board components that are heat sensitive.
Mounting Process of the PCBA Design
For the pcba design, there are two major mounting technologies utilized.
Through-hole Technology: This technology functions well on components having wires or leads that should be placed on the board. This is achieved by plugging them via holes. Soldering must be done on the board’s other side. You can apply this technology on any PCB assembly that contains large components like coils, capacitors, etc.
Surface Mount Technology: Components that are sensitive like diodes or resistors are automatically placed onto the board’s surface. For all surface mount devices, this is referred to as SMD assembly. You can apply surface mount technology on integrated circuits and components having small size.
Due to the distinct natures of both the surface mount and through hole technologies, they usually undergo varying assembly processes too. As we continue with the article, we will be discussing other pcba design and material considerations asides from the PCB base, with respect to how they apply to the pcba design process in relation to surface mount technology, through hole technology, and the mixture of both technologies.
Preparatory Steps to the PCBA Design Process
There are a few steps that should happen before the commencement of the real PCBA design process. This step assists the manufacturers of PCB in assessing the pcba design functionality. This also involves a DFM check.
Majority of companies that specialize in the assembly of pcb will need the PCB’s design file to begin. This includes other notes for the design, and some other important requirements. All these are necessary, so that the company involved in the pcba design can go through these files for any possible problems that can affect the manufacturability and the functionality of the PCB. This pcba design is for DFM check or manufacturability check.
The DFM check considers all the PCB’s design specifications. Most especially, the check searches for all redundant, missing, or possible problematic features. One or more of these issues will affect the final project’s functionality negatively and severely. For instance, a well-known PCB flaw in design is having to leave very little spacing between the components of the printed circuit board. This could lead to shorts, as well as other malfunctions.
When you identify these problems before the stage of manufacturing sets in, DFM checks can reduce the costs of manufacturing and get rid of unforeseen costs. This is so because these checks will reduce the scrapped boards.
Actual Steps of the PCBA Design
The actual steps of the pcba design come in steps:
1st Step: Solder Paste Application
The first move to make in pcba design is the solder paste application to the board. The process is likened to screen-printing on a shirt. The only difference is, instead of using a mask, a stainless steel and thin pencil is placed over your printed circuit board. With this, assemblers will be able to apply just the solder paste to some parts of the expected printed circuit board. This is where the components will be when the PCB is completed.
This solder paste is grayish and consists of minute metal balls, also referred to as solder. The tiny balls composition is about 96.5% tin, 3% of silver and 0.5% of copper. This solder paste has to be applied to these boards at the right and exact places. They should also be added in the right amounts.
In the line of professional PCBA design, the solder stencil and the PCB are held in place by a mechanical fixture. This solder paste is then applied on the expected areas by an applicator in the right amounts. This paste is then spread by the machine across the stencil, and this is done evenly to all open areas. When the stencil is removed, the solder paste stays in those locations.
2nd Step: Pick and Place
The next step here of the pcba design process is the use of the pick and place machine. Here, a robotic device helps in placing the SMDs components of the surface mount on an already prepared printed circuit board. The SMDs are now soldered to the board’s surface during the next stage of the pcba design process.
Normally, this process is a manual one done using tweezers. Here the assemblers will have to pick the components and place them by hand. Thankfully, these days, this has become an automated process. This shift happened largely due to the fact that machines seem to be consistent and accurate compared to humans. Although humans have the ability to work effectively, eye strain and fatigue can come in after some hours while using these small components. Machines can work non-stop without any fatigue.
This device starts this process by using a vacuum grip to pick up a printed circuit board and then move it back to the station. The PCB is then oriented by the robot at the station. It then starts the SMT application to the surface of the printed circuit board. The placement of these components is usually done on the soldering paste’s top in locations that have been reprogrammed.
3rd Step: Reflow Soldering
As soon as the surface mount and solder paste components are in the right place, then they have to stay there. What this means is that the solder paste has to solidify and also adhere to the board’s components. The process through which the printed circuit board assembly achieves this is referred to as “reflow.”
Once the process of pick and place is concluded, the board of the PCB is then moved to the conveyor belt. The belt passes through a reflow oven. The reflow oven is made up of some heaters that heats the board gradually to temperatures of about 250 degrees centigrade. This temperature is more than enough to get the solder melted in the paste.
Once the melting of the solder occurs, the printed circuit board keeps passing via the oven. This pcb goes through some cooler heaters that permits the solder, which has been melted to cool and then solidify. This helps in creating a final solder joint that connects SMDs to the printed circuit board.
Majority of pcba designs need some special consideration if reflow is going on. This holds most especially for pcba designs of two sides. Two-sided pcba designs require that each side is reflowed and stenciled separately. To do this the side having the smaller and fewer parts is first stenciled, then placed, and finally reflowed. Then, you do for the other side.
4th Step: Quality Control and Inspection
Once you have soldered the components of the surface mount in the right place, you will need to test the functionality of the board that has been assembled. In most cases, movement occurring during the process of reflow will lead to poor connection or there will be no connection at all. Another well-known side effect here is shorts. This happens when components that are misplaced connect circuit’s portions, which it is not meant to connect.
Looking for these misalignments and errors may require one of the several different methods of inspection. Below are the most common of the inspection methods.
Manual checks
Even though there is a great development of smart and automated manufacturing, during the pcba design, the use of manual checks are still paramount. For batches that are smaller, a very good way of ensuring that a PCB has great quality after the process of reflow is by a designer having a visual inspection.
However, as of today, this method is becoming very inaccurate and impractical as there is an increase in the number or quantity of inspected boards. Taking a look at these minute components for over an hour could result in optical fatigue. This could then lead to reduced accurate inspections.
X-ray Inspection
This is another inspection method. But this time, it involves the use of x-rays. This method is less common. This is used most frequently for more layered or complex printed circuit boards. This X-ray permits views to have a clear vision through the layers, as well as have good vision of the lower layers. This will help in the identification of all hidden problems.
A malfunctioning board’s fate depends on the standards of the pcba design company. These boards will be returned, so as to be reworked and cleared or even scrapped. Whether these errors are found by inspection or not, what to do next in the pcb design process is to carry a test on its parts to ensure that it performs the exact function it is meant to. This has to do with testing the quality of the pcba design connections. Boards that require calibration or programming will require further steps to ensure the functionality is tested properly.
These inspections can take place regularly and should be done after the process of reflow. This will help in identifying any possible problems. These checks can make sure that any error is found and also fixed quickly. This helps both the pcba designer and the manufacturer save materials, labor, and time.
5th Step: Through-Hole Insertion of the Component
Depending on whatever board type under the pcba design, this board may feature different components asides from the normal SMDs. Examples here are PTH, through-hole, or plated components.
A through-hole that is plated is a hole inserted in a PCB, which is plated through the board. Components of pcb utilize these holes for passing signals from one of the board’s sides to the other. For this case, the use of soldering paste will not be necessary. This is because the paste will only run through that hole straight without any chances of adhering.
Instead of using soldering paste, components of PTH need a very special soldering method during the latter stages of the pcba design process.
Manual Soldering
This process is straightforward. This involves a person tasked with the insertion of a component to a specific PTH. Once done, this board is then moved to the following station. Here another person will be working to insert another component. This is how the cycle goes on for the PTHs that require outfitting.
Wave Soldering
This soldering type is manual soldering handled in an automated way. However, this has to do with another process entirely. Immediately the component of the PTH is place appropriately, the board is placed on a different conveyor belt. Now, this belt runs via a specific oven where a molten solder wave washes the board’s bottom.
6th Step: Last Inspection and Test for Functionality
Once the pcba design soldering step is completed, there will be a last inspection to test the functionality of the PCB. This inspection is called the “functional test.”
After the PCBA Design
The simple truth is that the pcba design process could be a huge one. Soldering paste usually leaves back some flux, while handling done by humans could lead to the transfer of dirt and oils from clothing and fingers to the surface of the printed circuit board. Once this is completed, the results could look a bit gloomy. This is both a practical and an aesthetic issue.
After remaining on a printed circuit board for months, the flux residue begins to smell and get sticky. Also, it becomes acidic. This could cause damage to solder joints with time. In addition, the client’s satisfaction seems to take a hit when new PCB shipments are packed in fingerprints and residue. Due to these reasons, it is very important to wash the product after completing all the steps involved in soldering.
The best tool to use in getting rid of residue from your printed circuit board is stainless-steel washing apparatus of high pressure utilizing deionized water. Washing of printed circuit boards in any deionized water will not pose any threat to the whole pcba design. This is possible because it is the ions found in regular water, which causes damage to circuits.
Conclusion
Pcba design must pass through a technical and complicated process. Numerous elements must be considered carefully. Also, any little modification may cause a huge change in the quality of the product, as well as the cost. Description regarding the pcba design process centers on the pcba technologies and procedures.
The practical process of manufacturing is influenced and determined largely by the customer’s specific needs, requirements, and design files. Due to this reason, the ways of evaluating a reliable assembler of PCB has become a very important question for customers to answer before placing an order for their pcba design.
