Blog  /  PCB Assembly–What Should You Know About it?

PCB Assembly–What Should You Know About it?

PCB Assembly-- Selecting a PCBA manufacturing firm for your project may end up being a challenging task. However, there are ways you can use to narrow down your options.

When you are in the market for a PCB firm to source your PCB, you need to be aware of several important issues.

Some of the things you need to factor in include their production capabilities, customer service record, flexibility and responsiveness, and quality standards, to mention but a few.

This article is all about PCB assembly and what you need to know about it.

PCB assembly process

(PCB assembly process)

 

1. What is the PCB Assembly?

 

Referred to as PCBA in short, printed circuit board assembly or placement of components on the already fabricated PCB.

PCBA is slightly different from printed circuit board manufacturing, which deals with the circuit board’s fabrication.

Assembly is all about placing various components on an empty board to develop a fully functioning board.

Assemblers can achieve the placement of components either manually or mechanically. Mechanical assembly is the best choice based on its accuracy and precision.

 

2. PCB Assembly Type 

 

Electronic designers in many parts of the globe tend to experience challenges in getting their prototype boards ready for testing and use.

For this reason, PCB assembly services and technologies are a necessity for them.

With the right assembly and technology, it's possible to manufacture high-quality PCBs that will function as desired.

At this point, we will briefly highlight several PCB assembly services and technologies.

1. SMT Assembly (Surface Mount Technology)

A method whereby electrical components get mounted directly onto a PCB’s surface.

SMT components usually are PCBs' surface face more than through-hole counterparts based on their short leads.

2. Mechanical Assembly

mechanical assembly of PCBs involves putting together PCB components in an assembly line.

Additionally, it also refers to assembled parts or products made in this manner. It's putting products together to perform a specific function.

3. BGA Assembly (Ball Grid Array)

Ball Grid Array, also known as BGA in short, is another surface mount technology package.

IC, with many pins, mainly use this type of technology.

BGA is a low-cost packaging and high-density method that is ideal for bringing out some of the best circuit boards due to precision component placement.

4. Cable Assembly

a cable assembly is a group of wires or cables arranged into a single unit. Mostly, cable assembly can transmit power.

Also, cable assemblies are used for sending informational signals and provide power to several cables while organizing them in a package that's easier to maintain and replace.

5. Axial Horizontal Assembly

axial leads protrude from every end of cylindrical or box-shaped components.

Axial-leaded components do resemble wire jumpers in terms of shape. They are mainly used to span short distances on a PCB.

Axial horizontal assembly comes in two configurations: right-angle through-hole and surface mount.

Here, leads do come from the opposite ends of the component.

6. Turnkey Assembly

A turnkey refers to a product or service ready for immediate use by the person purchasing it.

When applied to PCB assembly, the supplier gets to handle the printed circuit board project's fundamental aspects.

It includes parts/components procurement and the manufacture of a PCB.

7. Radial Vertical Assembly

Radial vertical assembly involves placing components on a bare PCB hen the board area is limited.

Here, the order of components is done upright on the printed circuit board.

When talking of radial vertical assembly, leads do come from one end of the element.

8. Box-Build Assembly

Box-build assembly also goes by the name systems integration. Box build community is a complete assembly of the customer's finished product.

The box refers to a PCB assembly in a cabinet that's full of wires, a small enclosure, or a fully integrated electromechanical system with electronics and pneumatics.

9. Lead-free soldering

in commercial use, lead-free solders may contain tin, silver, copper, bismuth, zinc, indium, antimony, and other metal traces.

Lead-free soldering is the process of soldering by using lead.

However, it's important to note that soldering with tips may produce fumes and dust that may be adequately hazardous.

10. Printing

PCB printing refers to transferring the layout and PCB schematics on glossy or photo paper for final production.

For the best results, the print output needs to be in the form of a shiny one side.

Printing is a critical step in the manufacture of a PCB. When done wrong, the results can be disastrous.

11. N2 System

N2 refers to a molecule of nitrogen gas. Nitrogen is a colorless and odorless gas that finds a lot of use in the manufacture of PCBs.

N2 system is the use of nitrogen gas with PCB manufacturing, including reflow soldering and selective soldering.

N2 unique method for preventing oxidation problems and convection reflow.

12. PCB Assembly: Varnishing

Varnish coating applied to the surface of the printed circuit board. The main aim is to protect the board and all its parts from corrosion and damage from the external environment.

Varnishes help PCBs to withstand harsh environmental conditions.

13. PCB Assembly: Testing

Printed circuit board testing is an essential step in the manufacture of PCBs. With tests, manufacturers can detect errors and rectify them early enough.

This way, they'll be avoiding additional costs that come with the need to do reworks. With tests, there's a detection of errors that may cause the board to malfunction.

14. Packaging

Printed circuit boards have to resist physical breakage and be out of moisture. Insufficient packaging is a matter that may affect the proper functionality of the board.

For better features of a commission, adequate packaging is essential. If you want to have PCBs that will function properly, make sure your manufacturer uses proper packaging.

 

a picture of a PCB exposed to SMT

(a picture of a PCB exposed to SMT)

 

2.1 PCB Assembly: SMT Assembly

 

Surface Mount Technology or SMT, in short, is a process of fabricating PCBs by the use of a through-hole approach.

SMT's idea is to eliminate the need to make the leads of the components going through the PCB.

SMT is the first approach to PCB fabrication today. SMT is efficient, faster, and cost-effective.

 

2.1.1 Introduction to Surface Mount Technology

 

Surface Mount Technology was introduced way back in the 1960s, gaining popularity in the 80s.

Earlier, SMT technology went by the name planar mounting. SMT, unlike through-hole, doesn't require the drilling of holes on a PCB.

SMT involves picking and placing components of a circuit on a bare board.

 

2.1.2 Advantages and Disadvantages of SMT PCB Assembly

 

There are several advantages and notable demerits that come with SMT PCB assembly. A more significant gift here includes placing more components in a smaller space without any difficulty as such.

Additionally, manufacturers can save on assembly costs. It is because the manufacturer does not need to use a lot of materials.

Furthermore, the SMT PCB assembly ensures the manufacture of boards with the ideal weight.

Soldering components directly on the PCB does save a lot of room.

While there are benefits that accompany SMT PCB assembly, there are few demerits of this process worth noting.

With SMT PCB assembly, it's easy for components to break or drop during installation.

Additionally, as a manufacturer, you may have to invest heavily in SMT PCB assembly equipment.

Also, based on its technical complexity, high training and learning costs may be necessary.

 

2.1.3 SMT PCB Assembly Technology

 

Surface Mount Technology (SMT) is a type of printed circuit board assembly that involves getting parts of a PCB soldered directly on the surface of a PCB.

Surface mount technology is ideal compared to THT (Through-Hole Technology) that relies on drilled holes.

The following are what you may need to understand about SMT PCB Assembly Technology:

Development of SMT PCB Assembly Technology – as noted earlier, SMT PCB Assembly Technology is mounting electronic parts on a PCB board.

It's different from conventional board assembly that involves the insertion of components through holes. The idea behind SMT development was to reduce manufacturing costs and make efficient use of PCB space.

With SMT technology development, it's now possible to manufacture complex PCBs with excellent repeatability based on high automation levels.

Important Technology in the SMT Process – SMT is lately the most popular and widely preferred technology in PCBs’ assembly.

Since its advent, it has turned out to become the primary trend of electronics assembly.

One of the most critical technologies in the SMT process is the ability to set reflow soldering temperature so that the board’s components don't suffer from the heat.

 

 

2.1.4 How does SMT Machine Work? 

 

Surface mount technology machines, also known as robotic machines, are used to place a PCB on an empty board.

These machines are automatic and programmed to pick individual pieces and place them on a PCB.

Here, several subsystems work in unison to pick and place components on a bare board.

These machines are automated and rate every detail on a circuit board by using precise pre-programmed X-Y coordinates.

The SMT machine works through the following ways:

Component Placement – just as the name suggests, component placement involves using pick-and-place machines to place components on a bare PCB.

These components are known as surface-mount devices (SMDs).

SMT Printing – SMT printing involves printing solder paste onto a surface mount assembly to form a printed circuit board.

Finish SMT printing by using a template or metal mesh. SMT printing is an initial and vital part of the SMT process.

Reflow Soldering Process – The reflow soldering process involves a process in which we solder one or thousands of electronic components to the contact pads.

After this, the entire circuit board must withstand a certain amount of heat.

 

2.2 Through-hole 

 

Also called "through-hole,” it refers to the mounting of electronic parts that use leads on the details inserted into the holes of the printed circuit board drilled and soldered on the opposite side of the land. We can achieve by mechanically or manually.

 

2.2.1 Brief Introduction of Through-Hole Technology

 

Through-hole PCB assembly isn't a new concept as such and highly suitable for specific scenarios.

When you get to insert the leads of a component onto a circuit board, you are applying through-hole technology.

With this type of technology, it becomes possible to attach all the details of a PCB to the circuit’s inner layers.

 

2.2.2 Advantages and Disadvantages Of Through Holes and SMT Assembly

 

As of now, you must be fully aware that modern PCBA design heavily relies on two methods:

Through-Hole Mounting and Surface Mounting. Both of them have their respective advantages and disadvantages worth noting. Let's start with through-hole first.

 

Through-hole:

 

This method is ideal for THM’s advantages as it offers strong

mechanical bonds compared to SMT. THM is highly suitable for components that get subjected to mechanical stress. Also, THM is suitable for conducting tests and prototyping.

On the other hand, there are a few notable demerits with THM. For instance, this process is tasking to undertake as it demands precise drilling of holes on a bare PCB.

Additionally, THM tends to be slightly expensive when compared to SMT. THM may also be a less reliable method as some components may be fixed on the board manually. Man is prone to error.

 

SMT Assembly-Surface mount technology:

 

SMT is one of the best PCBA technologies out there. It comes with some advantages. For instance, with SMT, it's possible to manufacture small-sized but highly effective PCBs.

SMT is also a low-cost procedure, not forgetting that it's even faster. With SMT, there's high accuracy based on the use of specialized equipment here.

Unfortunately, though, there are some disadvantages associated with SMT. For instance, it can be unreliable, primarily, if used as the only attachment.

Additionally, SMT isn't ideal for circuits that may get exposed to rapid vibrations and stress.

 

the underside of a PCB subjected to PTH

(the underside of a PCB subjected to PTH)

 

2.2.3 PCB Assembly-- Through-Hole Component Insertion

 

Also known as "thru-hole,” through-hole technology is the mounting scheme used for electronic components.

Relates to the through-hole using a wire element are inserted in part. We insert the wire into the hole to drill a spot on the PCB and then solder it to the pad on the other side by manual or wave soldering.

Manual soldering is placing the components by use of hands.

In wave soldering, we need to use special equipment (wave soldering).

Wave soldering gets its name since it uses molten solder waves to attach metal components to the printed circuit board.

 

3. PCB Assembly-- Differences Between Through-Hole and SMT Assembly

 

Having to choose the type of printed circuit board assembly technique can be a difficult task.

Which one is the best? Is SMT assembly the right choice compared to the through-hole crowd or the other way around?

This section highlights ten differences between the through-hole and SMT assembly.

By the end of this section, you'll determine the best PCB assembly ideal for you.

 

3.1 Differences between Spaces

 

In SMT, there's a possibility of mounting more components with ease based on two factors.

First, SMT elements tend to be smaller. Secondly, these components can easily fit on both sides of the board.

Space problem is an issue in through-hole technology with the possibility of having parts on both sides of the board difficult.

 

3.2 Higher Pin Count In SMT Assembly than Through-Hole Technology

 

When it comes to pin count, SMT differs from through-hole technology, as SMT PCBs tend to hold more pins.

With technology continuing to evolve, there has been a slight elimination of leads that accompany through-hole technology.

 

3.3 SMT Assembly Components Are Usually Cheaper Than Through-Hole Components

 

In terms of costs, you'll notice that SMT assembly components are slightly cheaper than through-hole pieces.

If you opt for through-hole technology, you have to pay some extra fees when purchasing parts.

Again, this is why many people prefer SMT technology since it's an easy task to carry using affordable pieces.

 

3.4 PCB Assembly- Surface Mount Technology Is More Helpful For Assembly Automation

 

SMT heavily relies on automation as opposed to PTH technology. For this reason, it's possible to manufacture large batches.

With the possibility of producing large sets, manufacturing firms can also save on the costs of manufacturing.

With automated assembly, PCB manufacturers will save a lot of time to use to do other things.

PTH technology isn't ideal for automation, hence the slow production of circuit boards for those who prefer it.

 

3.5 PCB Assembly-- Through-Hole Technology Pays More Attention to Performance

 

Something ideal about PTH technology is that it produces panels that can function appropriately in high-heat environments.

PTH technology is a secure process that produces boards with the ability to withstand shocks and vibrations. Boards manufactured using PTH can easily withstand stressful conditions.

 

3.6 PCB Assembly-- The Technical Cost Difference Between Through Hole and Surface Mount

 

Without a doubt, the cost of PCBs made using PTH technology differs from those that underwent SMT.

Through-hole involves drilling leads on a PCB to hold all the components together.

Drilling is time-consuming and costly, unlike picking and placing pieces on a circuit board.

At times, members may have to be soldered to the board manually.

For this reason, the cost for circuits that underwent through-hole technology tends to be high.

 

4. How to Choose PCB Assembly Technology

 

Selecting PCBA technology depends on a lot of issues. If you are on a budget and need boards that will serve you properly, you can opt for those made under SMT technology.

If money isn't a big problem, then through-hole assembly may suit you. That's not all.

Do you want boards that will be able to withstand repeated vibration and stress?

If so, then through-hole technology is the right PCBA technology to use.

SMT assembly is easy to undertake compared to the through-hole crowd. Again, this is a factor that you need to consider.

 

5. PCB Assembly Process

 

The following is the actual PCBA process. While there’s no standard way of doing so, the following are five ways of PCBA:

Step 1: Solder Paste Stenciling

This is the first step of PCBA. It involves the application of solder paste to a bare board.

The solder paste is a thin and stainless-steel material. The parts where the paste is applied are where the pieces will sit on a complete PCB.

Step 2: Pick-and-Place

After assemblers are done with solder, picking and placing components follows. Mostly, this is a process achieved by the use of a unique robotic machine.

While such is achievable manually, machines are the best based on their accuracy.

Step 3: Reflow Soldering

The moment the solder paste and the components are rightfully in their place, they have to remain there.

For assemblers to achieve this, they must ensure that the solder paste solidifies to adhere to the board’s components.

Fortunately, this is achievable through reflow soldering.

Step 4: Inspection and Quality Control

After completing reflow soldering, the board needs inspection for quality control. Inspection checks for the functionality of the board. Here, the board is checked for matters to do with quality.

Step 5: Final Inspection & Functional Tests

After quality checks, final tests follow. These tests identify errors before a board can go into full manufacture.

The primary role of these tests is to avoid costly mistakes once the board hits the market.

 

6. PCB Assembly--Inspection and Testing

 

There is nothing more unpleasant than ordering faulty PCBs that won't work well in your electronic devices.

To be on the safe side, you need to ensure that you contain PCBs inspected and tested for functionality.

As a manufacturer, you'd want to minimize the costs of having to redo PCB manufacturing.

You will achieve this by subjecting your PCBs to inspection and tests before releasing them to the market.

You need to ensure that you submit your boards to design for manufacturability tests.

When undertaking inspection and quality control, you may choose either an X-ray inspection or manual checks, depending on your budget.

  • X-ray inspection is the best since it inspects hidden features on the PCB.
  • Manual tests are cheap but may not bring out the desired results as man is prone to error.
  • Lastly, you may have to consider the use of Automatic Optical Inspection (AOI). AOI is a crucial technique used in the production and test of printed circuit boards. AOI enables accurate and fast inspection of electronic assemblies to ensure that the product’s quality is high.

 

7. PCB Assembly Failures and their Prevention Methods

 

Failure 1: PCB Crack or Bend

 

The Reason:

 

A board may crack or bend during printed circuit board assembly due to high mechanical and physical stress.

A rigid PCB may fail if subjected to thermal shocks or repeated vibrations.

Also, flexible PCBs can crack if a bending strength goes beyond its capability.

 

Prevention method:

 

The best prevention method for cracks and bends is to ensure that it is pre-baked and stored in humidity-controlled cupboards.

Water can bring about shocks at the later stages of PCB assembly.

These types of cabinets during printed circuit board assembly A remove any water content in the bare PCB.

 

Failure 2: There is Apparent Polarity in the Components of the Assembled PCB

 

The Reason: 

 

While designing a PCB, there is a high possibility of forgetting to mention its parts’ contradictions.

If the ingredients’ opposition is not apparent during PCB assembly, it may bring about issues to do with reverse polarity.

As an example, connecting a battery with opposite poles can damage the electrical parts of a PCB.

 

Prevention method:

 

To do away with this issue, you may have to use a Schottky diode to avoid reverse polarity.

Connecting a diode in a series with the battery shuts off the circuit if there's an opposite polarity.

Such prevents damage during PCB assembly.

 

Failure 3: Joint Solder Fracture

 

Reason:

 

Fracture on the solder joint may occur due to differences in thermal coefficients of the PCB.

The printed circuit board could fail if exposed to environments where temperatures are high.

Also, manual soldering can be another cause of solder joint fractures. Manual soldering doesn't produce excellent results.

 

Prevention method:

 

To avoid instances of solder joint fractures, you may have to use specialized automatic equipment when soldering electrical parts on a PCB.

Also, ensure that you use the right amount of solder so that pieces of a PCB do not come off quickly during vibrations.

 

Fault 4: Printed Circuit Board Corrosion 

 

Reason: 

 

Flux is an essential component used in the manufacture of a printed circuit board. When not appropriately cleaned, flux residue may bring about corrosion to a printed circuit board.

While flux ensures construction-secure connections on a PCB, it may decay on a PCB, especially if it comes in contact with moisture.

 

Prevention method:

 

The main component of flux is an organic acid, such as adipic and citric acids.

To ensure corrosion avoidance, manufacturers need to thoroughly clean the printed circuit board to eliminate the remaining flux on the PCB.

For instance, if a manufacturer uses reflow soldering machines, corrosion is advisable to rinse off the remaining extra change.

 

Fault 5: The Component is Burned or Burned out (short circuit)

 

Reason: 

 

Short circuits are a common occurrence during the manufacture and assembly of PCBs. Short courses may occur due to moisture, solder bridges, or high current spikes.

These can cause damage to the entire board or instances of fires on electrical equipment.

 

Prevention method:

 

To avoid this, you may have to conduct a visual inspection to check for the possibility of hanging parts on the surface of a PCB. Also, you may have to carry out electrical testing to check for any open or short circuits.

PCB designers can also avoid instances of short circuits by properly aligning the layers of a PCB. With proper alignment of layers, it becomes hard for short courses to happen on a circuit board.

 

Fault 6: Copper Weight is not Suitable 

 

Reason:

 

For the flow of electricity to take place properly on a PCB, the copper foil’s right weight is necessary. If the copper’s value tends to be too thick or too thin, the PCB won't function as desired.

When designing a PCB, you need to ensure that you use copper foil of the ideal weight. Four ounces per square foot is considered the standard value.

 

Prevention method:

 

As a PCB assembler, you have to follow the standard copper weight specifications to avoid having PCBs whose copper weight isn't ideal. It shouldn't be too thick or too thin.

Thick ones may see you incurring additional costs, while thin ones may experience several instances of overheating.

 

Fault 7: The Component Position Has Moved 

 

Reason:

 

When it comes to PCBs’ assembly, pick-and-place machines mostly carry out picking and placing a PCB on a bare board.

If the details shift or move during soldering, then the whole assembly will be a complete failure. When elements go, you may end up with an open circuit.

 

Prevention method: 

 

As an assembler who wants to avoid such a scenario, you need to follow the recommended humidity and temperature requirements.

Also, you may have to use the best pick-and-place machines known for the accurate placement of components.

Furthermore, you may have to use an aggressive flux to hold all the parts and make them stay in position.

 

Failure 8: Component Warranty May Be Less

 

Reason:

 

When it comes to the assembly of a printed circuit board, you need to ensure that your manufacturer uses some warranty components.

If the component warranty is less, then you may end up with panels that will fail after a short time of use.

 

Prevention method:

 

To prevent such, you need to ensure that your manufacturer uses high-quality components with several years of warranty.

Don't go for boards whose parts have a limited or short warranty period, as it may be costly on your end.

 

Failure 9: De-wetting Due to Melting Solder 

 

Reason:

 

De-wetting takes place due to problems with electric components or the solder pad itself. When de-wetting takes place, the solder joint becomes loose and fails to make secure connections. Some of the significant causes of de-wetting include corrosion, overheating, and contamination.

 

Prevention method:

 

PCB assemblers need to carry out careful board inspection, prepare it properly, and then carry out thorough cleaning.

A pencil eraser is one of the best equipment to use since it can quickly eliminate mild corrosion and rust.

Also, you can use a magnifying glass to check whether the coating is correct.

 

a damaged PCB resulting from a short circuit

(a damaged PCB resulting from a short circuit)

 

 

8. PCB Assembly Provider

 

Are you struggling to find the best PCB assembler? If so, then worry not since you are not alone.

Here are essential things to note if you want to make your PCB assembly a success.

When looking for a PCB assembly provider, there are critical factors that you should not ignore.

If you’re going to have high-quality boards that will function for a long, you must consider several things concerning your potential provider.

 

Get in Touch With Your PCB Assembly Provider

 

First, you need to get in touch with your PCB assembly provider and hold a discussion before beginning anything.

You can reach your assembler via phone, email, telephone call, or any other means.

It is essential to communicate with your assembler at the design stage to end up with the product you want.

 

PCB Assembly-- Offshore Providers May Be Good, But Not Always

 

Secondly, you may want to source your PCBs from offshore providers.

You need to be aware that while offshore providers may be right (especially in terms of high-quality goods and affordability), there are some risks associated with offshoring.

Some of the dangers here include production delays and poor handling during shipping.

 

Don’t Count on a Single Supplier.

 

Lastly, you do not have to count on a single supplier. Relying on a single supplier somehow puts you in a desperate position.

You need to have enough suppliers so that you can choose.

This way, you will ensure that you have another one to source your PCBs if one supplier fails you.

 

PCB Assembly--Pay Special Attention to File Formats

 

When it comes to PCBs’ design and manufacture, you'll often hear the term file format.

This file format can create the physical layout of the printed circuit board.

The file format we save in standard ASCII text format. When it comes to the file formats, you need to consider naming and labeling parts.

You need to mark and label the components that are in your package. They must know to avoid errors.

Secondly, you need to recheck all trade-offs. Do you want a printed circuit board with more power?

Or are you looking for one with a more robust transmission? Do not let matters to do with trade-offs scare you.

While you may have to scale back a little bit, you don't have to drop everything.

If need be, you may have to talk to your manufacturer and find tips on how you can go about improving the design to meet the requirements.

 

Summary 

 

Are you in the market for the best-printed circuit board assembler? We at OurPCB are ready to assist you. Printed circuit board assembly is not a difficult task to undertake.

But if you are inexperienced or choose to partner with the wrong firm, you may end up with low-quality boards.

OurPCB is a group of experienced professionals ready to offer you state-of-the-art PCB Assembly and Manufacturing services.

We encompass the latest technology while assembling your boards. With us, rest assured of high-quality panels that go into quality control and functional tests before hitting the market.

I believe that after reading this article, you’ve gained a lot of knowledge of PCBA. You can contact us by email, and we can discuss more PCBA together and establish a friendly relationship.

 

 

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