Monday, July 11, 2022

Four Stages of PCB Design and Assembling


 

PCB is a printed circuit board that helps connect different electrical components. The board is a combination of laminated material, and the copper foil laid on a non-conductive substrate.

A PCB is the main part of any electronic device, so it has to be perfect. It should have functional components and microelectronics circuits to perform well. Development of PCB goes through different processes that you should know well. PCB manufacturing has 4 stages, including design, manufacturing, PCB assembly, and PCB testing.

First Stage- Design

PCB design involves different steps, such as schematic design, layout planning, the placement of the components, routing, and manufacturing files.

PCB schematic design: It is a blueprint of PC design that shows all PCB components with symbols. The schematic design is always according to the technical requirements of the user.

Layout planning: After the schematic design, you have to develop the layout of a PCB that includes physical components’ models, the shape of the PCB, and the structure of a PCB.

Placement of components: It involves planning the placement of various components. You decide on the PCB layers according to your requirements. The right placement of the components ensures a flawless board, decreasing the production cost.

First of all, the designer places the fixed components in the layout, including switches and connectors.

Then, the critical components are placed, such as memory chips, microprocessors, as well as power supplies.

Then the supporting components of the PCB are placed, like inductors, capacitors,  and resistors.

In the end, the decoupling capacitors and terminating resistors are placed.

Routing: Once the components are placed, you have to connect all components through trace routing. There are four ways to do so, such as manual routing, auto-interactive routing, semi-automatic, and batch-auto routing. You can choose any method according to your Printed Circuit Board and budget.

Design: In this stage, you have to plan for the number of board layers, dimension of the board, and types of components. You can use a special app in this case, such as EDA or electronic design automation. The designer often adopts the SMT instead of a through-hole technology, depending on your requirements. Once the design is over, you can export the design files to CAD or Gerber format.

Preparation of manufacturing files: This is the last stage of design where the designer exports the Gerber files for manufacturing. The manufacturer needs these files to develop a printed circuit board.

 

Stage 2-Manufacturing of Circuit Board

Once the manufacturer receives all design drawings, he starts making PCB. It involves different stages as described below:

Design Imaging: The manufacturer uses a plotter to convert the PCB design files into films like they resemble the photo negatives of the schematic design. The printer uses black and clear inks for inner and outer layers. Copper traces and circuits are shown with black ink, whereas the non-conductive parts are shown with clear ink.

Printing of Inner Layers On Copper: It is the initial stage of PCB manufacturing. The engineer uses a substrate material to make a laminated board. Like, epoxy resin or fiberglass are common in this case. The design of the PCB is printed on the board, and then he pre-bonds copper on a board’s both sides. After that comes the etching of copper, and then the board is protected through a photo-sensitive film.

Ultraviolet Light: the manufacturer then exposes the resist-covered PCB to UV light to strengthen the photo-reactive material. Then the board is cleaned with an alkaline solution to get rid of unnecessary copper particles. The expert checks the board to remove any errors and then goes to the next stage. The main aim of UV blasting is to develop a PCB  Board according to the schematic drawing.

Inner layer’s etching: copper’s inner layer needs chemical etching for removal. The process of photoresist prevents the essential copper from etching. The board size determines the amount of the solution and etching time which is less for small boards but more for large boards.

Some other manufacturing processes include:

·         Alignment of layers

·         Optical testing

·         Layer pressing and lamination

·         Drilling

·         Plating of PCB

·         Imaging of external layer

·         Etching of external layer

·         Solder mask

·         Silk screening

·         PCB finishing

·         Testing

·         Profiling

·         Quality testing

·         Packaging of PCB

·         Shipping of PCB

 

Stage 3-PCB Assembly

The assembly of a PCB involves four stages, such as soldering, placement of components, solder pasting, and testing. Let’s review them in detail.

Solder Pasting: It is like t-shirt screening, as it involves solder paste stenciling. The stencil is made of stainless steel and it’s very thin. You have to use the stencil to apply the paste in areas where different components will be installed. In this process, flux is used for melting the paste to help it bond to the PCB.

Placement of the Components: Once you are done with the solder paste, you need a pick and place the tool for the components. Generally, it is SMT or surface mount technology where components are placed on the PCB surface. Initially, it used to be a manual process and assemblers used tweezers to pick and place different components on the board. However, new technology has made this process automated due to robotics and it’s more precise and consistent.

Soldering of PCB: After the placement of components, you have to place the PCB on a conveyor belt to help a board move to a reflow oven that heats the board. The heating helps melt the solder paste, and bond the components on the board permanently. However, if the board has more components other than SMDs, it would need a through-hole insertion that involves more advanced soldering.

Testing of PCB Quality: Sometimes, the components are misplaced during reflow when the PCB is moving. This issue may cause a poor connection, or no connection at all, or the parts are not well-connected. So, you need to inspect the PCB to ensure a flawless function. A PCB can fail this test even if it passed other tests, and a failed PCB goes to scrap or you have to recycle it with all essential processes until you get a flawless circuit board.

 

Stage 4-PCB Testing

Manufacturers use different methods for PCB testing to ensure that it will function correctly. These methods include in-circuit, optical inspection, flying probe, turn-in, x-ray, and a functional test.

In-Circuit: It is also known as ICT, or you can call it the bed-of-nails inspection. In this method, PCB is pressed on the bed of probes. It is highly accurate because it checks all components of a PCB. You can also test the BGAs with this method. Moreover, it also tests the solder integrity of the bottom-terminated components.

However, this test is expensive and time-consuming. Moreover, it does not test the non-electrical parts and connectors.

AOI, Automated Optical Inspection: This testing method involves a visual inspection of the board. It is done with the help of HD cameras, LED lights, UV, and high-level infrared. The test is contact-free and helps check poor solder joints or missing parts. It also tests the smt assembly issues and it’s very accurate.

However, it only inspects the preprogrammed errors and can’t check defects regarding glue or sealing.

Flying Probe Test:  It involves probes that help test the upper and lower surface of a PCB. This PCB testing method is cost-effective, consumes less time, is easy to do, and is compatible with many applications of PCB assembly. However, it is slower than other testing methods and not ideal for complex testing.

Burn-In Test:  In this test, PCB is exposed to a high temperature to see if it works well. It ensures a lifetime product and enhances the brand because of an effective end product.

However, this test is costly and can affect a PCB by damaging its components. Moreover, it can be less reliable due to voltage scaling.

Inspecting Through X-Ray: It involves an x-ray machine that inspects a PCB. It thoroughly checks soldering which is hard to detect with AOI. The x-ray inspection is ideal for thick or multilayered PCBs. It also detects the voids or bubbles and can also check the components under a shield.

However, it needs expensive x-ray machines and can cause hazards in the workplace.

Functional Test of PCB:  It involves functional testers that you connect to the edge connector. It creates an electronic environment for which a PCB is made. It inspects the functional errors and identifies the analog issues. It also checks issues with digital circuitry.

However, it is very costly and needs high-end tools, which are too expensive. It needs a proper understanding of the working atmosphere of the DUT.

Final Thoughts

The development of a PCB involves different processes, including design, printing, assembling, and testing. Each stage is further divided into different parts, and you have to understand all stages to create a flawless PCB.

The board is a combination of laminated material, and the copper foil laid on a non-conductive substrate. A PCB is the main part of any electronic device, so it has to be perfect.

Would like to know more about the design or pcb assembly services stages? Email us at sales@pnconline.com

 

Monday, July 4, 2022

Physical and Electrical Partitioning In PCB Design


Partitioning your design into physical and electrical sections can significantly reduce the number of through-holes you need in your PCB, thereby increasing production speed and cutting down on manufacturing costs. Here, we will explain what physical and electrical partitioning are how they are used in PC design, and how to create effective partitioning schemes in your PCB designs.

As you work on your next PCB design, you may be wondering how to implement physical and electrical partitioning in your design. These two factors are equally important to making the finished product successful, and both have a huge impact on the success of your design project as a whole. Stay with us if you’re looking to save time and money while producing high-quality products, read on!

Layout Considerations

When you’re laying out a Printed Circuit Board, you have two different considerations, such as physical, which is how your components are laid out on your printed circuit board; and electrical, which has to do with where you're going to put all of your wires. These two can be grouped when it comes time for assembly.

For example, if you plan to use surface-mount parts that require soldering instead of wire-wrapping, then you will want to make sure that there is enough space between these parts so that they can be easily soldered onto your PCB. If you don’t leave enough space between them, then there won’t be room for solder paste. The solder paste is a sticky substance used to hold down SMT parts during pcb assembly.

This makes soldering difficult or impossible and the same logic applies to wiring. If you don’t leave enough space between components, then your wires may not fit without being bent too much or getting in each other’s way. This can cause problems when it comes time to solder everything together, as well as with heat dissipation, and too many wires crammed into one area might block airflow and cause overheating issues.

On top of that, you also need to consider things like trace width and spacing. Trace width refers to how wide your traces are (the lines connecting individual pads on your PCB), while trace spacing refers to how far apart they are from each other. Trace width should always be smaller than trace spacing because having wider traces means more copper is needed per unit length which means higher cost and greater weight.

Traces are usually made using either a single solid line or multiple lines connected by vias. Single solid lines tend to be faster but less reliable than multiple lines connected by vias, but they’re also easier to design and cheaper. Vias are holes drilled through layers of material that allow traces on different layers to connect.However, vias increase complexity and cost. There are several tools available to help designers create their circuits. Some free software options include EagleCAD, Kicad, Altium Designer, and CAD. However, regardless of what software you choose to use, remember that layout is only half of the process.

Overlapping Impedance Nets & Ghost Nets

To create a circuit board with electrical & physical separation, you must insert impedance nets into your design. There are three different ways you can do that, including overlapping impedances, creating ghosts, or through a virtual ground plane. In some designs, more than one method is used. So, let’s see how and when to use them.

 

An overlapping impedance net has part of it on one side of a barrier, and part of it on another side. A ghost net is used when you have two nets that need to be separated but you don't want them physically separated because they are too close together or because they are too important for each other. A ghost net is just a virtual representation of an actual physical connection that exists between two parts of your circuit board.

 

A good example of why you might use a ghost PC board net instead of separating your nets with some physical method is if you have 2 power supplies that need to share ground. They can share ground by having their grounds tied together through some kind of wire.But, since they're both supplying power independently, we don't want them tied directly together at all times, but only when there is a current going through either one or both supplies. So what do we do? We create a ghost ground plane where we tie their grounds together. This way, when none of the supplies is active, there's no connection between them, and when either supply is active, there is a connection between them.

 

An electrical partitioning net does exactly what it sounds like. It partitions electrical signals from each other. In a design where you want to physically separate your nets, you can do that by creating an impedance plane that separates them. But, then how do you keep them electrically isolated? That's where a physical partitioning plane comes into play. This is just another name for a ghost ground plane, but instead of being used for sharing grounds between two supplies, it's used for keeping two parts of your circuit board electrically isolated from each other while still allowing communication between them.

 

One last thing about these three methods is that you can't use one without using at least one of the others. If you have a wall between two sections of your circuit board, there has to be some way for those sections to talk to each other. Otherwise, they wouldn't be able to pass power or data. So, if you have a wall, you need ghosts or an impedance plane on both sides of it. And if you have ghosts, there needs to be a wall somewhere too.

 

Why Would You Ever Choose One Method Over Another?

 

 Well, overlapping impedances are good when you don't need high-frequency performance because they introduce more inductance than either of the other two methods. Ghosts are good when you don't care as much about electromagnetic interference or EMI because they don't create as much capacitance as either of the other two methods.

 

Whereas the physical partitioning nets are good when you want to keep your layout compact or if you have a design that's already laid out and you can't change it, as having a wall between two sections of your board is going to require some rework if it doesn't already exist.

So, you need to decide if you want your partitions at a high frequency or low frequency. For a high-frequency circuit board, you'll need to use overlapping impedances or ghosts; for a low-frequency circuit board, you can just go with physical partitioning nets.

Solving Unplanned Overlaps

It’s not uncommon for two different circuit boards or two different designs within a single board to overlap. Unplanned overlaps are hard to solve, but these tips will help you create better schematics so that you can avoid them.

Before you design your next PCB, make sure you follow all of these guidelines for PC Board Fabrication. By doing so, you’ll be able to identify overlaps before they occur and reduce your chances of creating any issues when manufacturing your product.

If you don’t have access to specialized tools or software, consider using some online tools like Google Sketch Up to help with your schematic design. These free programs allow you to build 3D models of your circuits, as well as export them into other applications like Eagle CAD or Altium Designer. This allows you to easily view how your components will fit together on a printed circuit board.

You should also use both software and hardware layout techniques to ensure that there aren’t any unplanned overlaps between your PCBs. While it may seem easier to just use one method, it’s important to understand how each technique works so that you can spot potential problems early on. For example, if you only use software-based layout techniques, then you might miss physical overlaps that would prevent a component from fitting onto your board.

Similarly, if you only rely on hardware-based methods, then you might overlook electrical conflicts that could lead to shorts or failures during testing. The best way to get around these kinds of issues is by using both types of layouts simultaneously. You can use a program like Altium Designer to lay out your circuit board, then print out an image of what you’ve created. Then take that printed image and place it over your actual PCB. This ensures that you catch any unplanned overlaps before they cause problems later on down the line.

Just remember, even though it takes more time upfront, double-checking everything twice is always worth it. With that said, there are still times when the overlap errors do slip through. When you find yourself in a situation where you need to resolve an issue like this, we recommend you double-check it. As it would become much easier to fix an error than it would be otherwise. You can also get professional help in this regard.

Would like to know more about physical and electrical partitioning in your designs or pcb assembly services? Write us at sales@pnconline.com