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The Most Comprehensive Guide to Printed Circuit Board Assembly

There have been many claims about the manufacture and manufacture of printed circuit boards, but little to do with printed circuit board assembly as a topic on its own. In this article, we will discuss ten things that you need to know about the printed circuit board assembly. 

 

Are you struggling to find the best-printed circuit board assembler? Are you afraid that the final output of your board won’t come out as you expected? If so, worry not. Here are some helpful tips that will make your printed circuit board assembly a success. Below are ten things that you have to know concerning the printed circuit board assembly. 

What is the Printed Circuit Board Assembly?

Also known as PCBA, printed circuit board assembly may be a very complicated concept to comprehend. But why, you may ask. The reason is that PCBA isn’t the same as printed circuit manufacturing, also referred to as PCB. Printed circuit board assembly and PCB manufacturing are two different disciplines with different requirements and standards. 

PCB manufacturing is all about the fabrication of the circuit board. On the other hand, printed circuit board assembly deals with the manufacture or placement of components or parts on the already fabricated board. 

Inside a PCB assembly firm.jpg

Preparation Before PCB Assembly

A printed circuit board is a critical concept in electronics. Sadly, a lot of people don’t understand the importance of a printed circuit board. Much worse, a lot of people aren’t aware of the composition and preparation before PCB assembly. The following are what you need to understand before PCB assembly. 

2.1 PCB design basis

Substrate – PCB substrate is the solid material that holds components and traces of a PCB. Before PCB assembly, you need to ensure that you use the right substrate material. Selecting the right substrate is the first step towards having the best PCB. In short, the right substrate materials mostly affect the performance of your PCB.

Copper – copper is one of the most common elements used in making traces. But why is copper a trendy choice across the printed circuit board industry? The most significant benefit that comes with copper is the fact that it’s highly conductive. Copper can properly transmit signals without losing electricity along the way.

Solder mask – solder mask is a layer found on the top of the copper foil. This layer gives a printed circuit board its green color. The solder mask is overlaid onto the copper layer to insulate copper traces and to protect copper traces of a PCB against cases of oxidation. The solder mask also prevents solder bridges from forming in between closely spaced solder pads. 

The green solder is the most common solder mask.jpg

2.2 PCB assembly requires electronic parts and consumables 

The construction of a printed circuit board is different from manufacturing a circuit board. The production of a printed circuit board involves several processes, such as designing and creating a PCB prototype. There are some things that you will need for a printed circuit board assembly. The following are electronic parts and consumables that you’ll need for PCB assembly:

Printed circuit board

The Electronics components

Soldering flue

Soldering equipment 

(wave soldering machine, soldering station, SMT equipment, inspection, and testing equipment). 

2.3 The three main types of PCBs

Printed circuit boards are mainly classified based on frequency, the substrate used, and the rate. Some of the most popular ones include the following:

•  Rigid PCB – Rigid PCBs are those types of printed circuit boards whose materials are fabricated from robust materials and can’t be bent. Rigid PCBs are compact and very easy to repair in the event of damage. If you are in the market for a PCB whose maintenance is easy, you better go or rigid PCBs.

•  Flexible PCBFlexible PCBs compose of flexible base materials. These types of PCBs come in double-sides, single-sided, and multilayer formats. Such helps in minimizing the complexity within the assembly of the device. Flexible PCBs are ideal in working conditions where density and temperature is the primary concern. 

•  Metalcore PCB: (FR4 board) – FR4 PCBs are lately finding use in a lot of electronic equipment. FR indicates that the material is flame retardant, while the 4 shows the four elements used in the production of these types of PCBs.

2.4Three installation technologies in the PCB assembly industry 

•  Surface mount technology – This is a method whereby a printed circuit board’s electrical components get mounted directly on the surface of the PCB. The electrical components installed in this way are surface mount devices (SMD). 

an illustration of surface mount technology.jpg

•  Through-hole technology – This is a mounting scheme used in electronic components involving the use of leads on parts inserted into the holes that are drilled in the printed circuit board and soldered to pads on the opposite side of the committee manually or automatically. 

•  Hybrid technology – Hybrid technology is also another accessible installation technology that comprises the use of dissimilar materials to optimize electrical performance and improved system reliability. 

2.5 DFM Inspection 

What is DFM inspection?

Also known as DFM in short, Design for Manufacturing involves the process of designing parts, products, or components for ease of manufacturing to make the end product at a lower cost. DFM inspection is the process of checking a printed circuit board for its functionality. DFM inspection involves a review of the bill of materials, parts not recommended for manufacturing, and components that require immediate replacement. 

Why do we need to conduct a DFM inspection?

There are plenty of benefits that come with DFM inspection. DFM inspection allows designers to understand the reproducibility and repeatability of a product. It also guides on tolerances during the manufacturing process and whether the demands of the product are reasonable. Some of the issues covered during DFI include checking how issues to do with tolerances will impact the gauging system and detect matters concerning non-conformances.  

Importance 

As mentioned earlier, design for manufacturing is the process of designing products to make them easy to manufacture. DFM is one of the most critical manufacturing tooling process development and tooling design steps before building a new product. 

DFM is essential when planning to design a new product. When it comes to the manufacture of PCBs, DFM is necessary because it can ensure product production. With DFM, products won’t quickly go back to the drawing board. Secondly, DFM is essential as it can affect your product’s feel, look, function, and precision. Lastly, DFM is necessary as it can significantly affect your timelines. 

How to Carry out the Detailed Steps of the PCB Assembly

Printed circuit board assembly isn’t a complicated process as such. However, when done wrongly or in a rush, you may end up repeating the whole process. There’s nothing much worse and costly than having to repeat PCB assembly. To be on the safe side, you may have to follow the real steps of PCBA as highlighted below:

First step: Print the Solder paste – When it comes to the PCBA process, you need to first apply some solder paste directly on the board. The process is the same as screen-printing of clothes and apparel, whereby you place a stainless-steel stencil over the PCB. It will now be the basis for creating a solder paste printing of new parts.

Solder has a composition of 3% silver, 95% tin, and 0.5%, copper. In a PCBA line, a mechanical fixture perfectly holds the solder stencil and the PCB in place. After that, an applicator will then smear some solder paste directly to the areas intended in the ideal portions. 

Solder paste printing in PCB assembly line.jpg

Second Step: Pick & Place

After the application of the solder paste, the PCBA process moves to the pick and place machine. Initially, pick, and the place was a manual method whereby you had to use a pair of tweezers to assemble all the elements of a PCB by hand. However, with improved technology, we now have robots automated to pick and place parts of a PCB. The robot also positions the PCB  appropriately and applies surface mounts to the surface of the PCB. 

Pick and place with tweezers during assembly.jpg

Third Step: Reflow Soldering

The moment the PCB elements and the solder paste are in place, they must adhere correctly. For this reason, the dough has to solidify to attach parts to the board through reflow. A majority of PCBAs need special consideration in the process of reflow, more for two-sided printed circuit board assembly. 

PCB after passing reflow soldering.jpg

Fourth Step: Inspection & Quality Control

The moment these elements get soldered into place, the board requires testing to determine its functionality. During reflowing, movement may result in a lack of connection or poor connections. We can complete the inspection and quality control manually or automatically. Despite smart and automated manufacturing, you still require to do manual checks when it comes to PCB assembly periodically. 

Unfortunately, manual assembly tends to be inaccurate. Automatic Optical Inspection is more appropriate and ideal for large batches. Here, PCB manufacturers use automated machines to process high quantity PCBs in a short time. 

Lastly, there’s an X-ray inspection. This type of inspection method is not common though it finds heavy use in complex and layered PCBs. With X-rays, a viewer can see through layers and subsequently visualize the lower layers to see hidden problems. 

A PCB x-ray inspection.jpg

Fifth Step: Through-hole assembly

Depending on the circuit board under construction, it could bear various elements that would not usually be on the surface mount devices. They may include plated thru-hole details or PHT.  Besides soldering paste, PHT components may require specialized soldering methods such as manual soldering or wave soldering. Manual soldering isn’t a complicated process. Here, an individual inserts elements into a designated PTH before transferring them to the next station. Manual soldering can be a very lengthy process, with many companies trying to avoid using it. 

Wave soldering is another PTH insertion method. Most people might refer it to as the automated version of manual soldering, but it is entirely a different process. 

Sixth Step: Final Inspection and Functional Test – After completing PCBA, you need to conduct the last inspection to assess the PCB functionality. This inspection puts the printed circuit board through its paces, replicating the likely and unlikely scenarios that it would undergo. Testing is essential as it determines the failure or success of the PCB. If it fails, the PCB can be scrapped or recycled. 

Final Inspection and Functional Test.png

13 Effective Test Methods for Printed Circuit Board Assembly

If you are thinking about PCBA, you need to be aware of PCB failure’s high costs. The last thing on your wishlist is seeing your PCB dropping dead without any warning. Here are 13 effective test methods for PCBA:

4.1 Why We Do A PCBA Test

PCBA testing is essential in the development cycle of a PCB. By conducting tests, PCB manufacturing firms can save funds that go into rework or recycling. With tests, there’s the avoidance of unnecessary costs. 

Bare Board Test

Bare board test involves testing the continuity and isolation of electronic connections on a bare/empty printed circuit board. This test is on the blank board before the attachment of essential parts such as ICs. 

Assembly Level Test

Assembly level tests are essential for checking the functionality of a PCB. These types of tests completable manually or by using automated test equipment. Mechanical test equipment tends to be a little bit expensive though the results are excellent. 

Online Test

Also referred to as automated tests for PCBs, you can undertake online checks after the manufacturing process of a PCB is complete. With online tests, PCBs are subjected to thorough inspection using a flying probe or adapter E-Test equipment. 

On –line testing of FICT Without Fixtures

Another name for a Fixtureless in-circuit test (FICT) is the flying probe test. It is a test that works without a custom fixture, thereby minimizing the overall costs of inspections. FICT uses a simple installation that holds the board as the test pins move and test relevant points on the PCB. 

Functional Circuit Test

This test is the final gatekeeper in the printed circuit board manufacturing plant. Functional circuit tests provide either a no-go or go choice on finished PCBs. 

Functional circuit tests check for the overall product. It is an analysis aimed at determining whether everything works in the right manner. 

Boundary Scan Test

We consider boundary-scan test checks for PCBs wire lines and a preferred means of testing PCBs, especially when it’s hard to reach the entire nodes of the PCB. Something good about this test is that it can quickly assess the whole board without the need to touch or reach all the board’s nodes. 

JTAG Test

Also known as the Joint Test Action Group test, is another crucial test for the manufacture of PCBs. The is necessary to verify designs in addition to testing PCBs after completing the manufacturing of a PCB. JTAG tests are cost-effective and strengthen the overall quality of the finished PCBs. 

X-ray Fluorescence Transmission  

This test is a test whose purpose is to view the internal construction of a PCB, including layers and vias. This test is also essential in verifying the authenticity of a PCB. With such tests, manufacturers can find and locate defects during the early manufacture of PCBs. Of importance to note is that such tests need to be conducted by highly trained experts. 

X-ray lamination system 

This type of test is closely related to X-ray fluorescence transmission that works by generating a focal plane. The focal plane gets created through the process of scanning, where an x-ray detector spins synchronously. This type of test identifies errors such as missing solder joints, misalignments, and inadequate wetting, among others. 

Ion Contamination Test

Close to 25% of PCB failure takes place due to ionic contamination. Also known as the resistivity of the solvent extract (ROSE) test, ionic contamination tests detect ionic tissues that remain behind after the process soldering. 

Chemical Resistance Test of Solder Mask 

The main aim of this type of test is to identify a solder mask’s chemical resistance. This type of analysis is not as complicated as such. However, when done wrongly, The result may not be the same as expected. 

Hardness Test of Solder Mask

This type of test aims at examining the hardness of a PCB’s solder mask. Just as the name suggests, this type of analysis checks the hardness of a PCB to determine whether it can function as intended. 

regardless of your choice of test, you should ensure that you conduct any of the above criteria.jpg

The Difference Between PCB Assembly, THT Assembly, SMT Assembly, and Hybrid Technology

5.1 Through-hole technology (THT) assembly process

Through-hole technology is the process of inserting components with leads and tails into holes that require drilling in the PCB. These boards are known as through-board components. These leads can then be soldered onto lands or pads on the board’s underside, mostly through a wave solder process. The following is the THT assembly process:

Step 1: Component placement

Component placement is an electronics manufacturing process involving the installation of electronic components on a printed circuit board for purposes of creating electrical interconnections between functional components and the interconnecting circuitry in the PCB.

Step 2: Check and correct

Check and correct is the second step in THT. Check and correct involves checking and correcting any errors on a printed circuit board, and checking aims at finding mistakes and fixing them before a PCB is ready for the market. 

Step 3: Wave soldering

Wave soldering is a large-scale soldering process involving the soldering of electronic components to a PCB to create an electronic assembly. The name gets derived from the using waves of molten solder to attach the metal components to the printed circuit board. 

Electronic chip component on the green printed circuit board.jpg

5.2Surface Mount Technology (SMT) assembly process

This technology is a method used in the assembly of electronic circuits. Here, components get mounted directly on top of the PCB using a piece of special equipment. Mostly, SMT components tend to be small, a reason as to why individual machines are necessary. The following is the SMT assembly process:

Step 1: Solder paste printing – This is a process whereby you apply solder paste directly onto a printed circuit board. You achieve this by writing solder paste using stencil apertures. 

Step 2: Component installation – Printed circuit boards consist of several components: capacitors, diodes, fuses, and resistors. Component placement is the process of installing all the parts that make up a PCB.

Step 3: Reflow soldering –This is a process whereby you use solder paste to temporarily attach hundreds or even thousands of PCB components on aboard. After the attachment of the parts, the entire board gets subjected to controlled heat.

Step 4: Wave soldering procedure – This comprises an extensive soldering process whereby electronic components are soldered on a printed circuit board to form an electronics assembly. Again, the name comes from the use of molten solder to attach metal components to the printed circuit board. 

It is the production line for surface mount technology assembly.jpg

5.3 Hybrid technology

A hybrid integrated circuit is a miniaturized electronic circuit made of individual devices such as transistors, resistors, and capacitors bonded to a substrate or a printed circuit board.  Hybrid technology assembly comprises of the following: 

Single-sided mixed assembly: In this type, through-holes and SMDs get mounted, but only on one side of the PCB.

Single-sided SMT and single-sided THT: Here, SMT technology is employed to mount SMD components on one side of the board.

Double-sided mixed assembly: – When it comes to double-sided diverse construction, SMDs get mounted on both sides of the PCB.

5.4 How to choose the right PCB assembly technology

There are plenty of things to consider when choosing your PCB assembly technology. If you happen to get it wrong, then there are high chances that you’ll end up with a weak printed circuit board that won’t function as desired. If you choose to outsource such as service, you have to ensure that you work with the right partner. 

To ensure that you are on safe hands, you may want to partner with an experienced firm that has been in business for long. Additionally, you need to follow an are appropriate timeline, not forgetting to evaluate your potential partner’s quality. Also, check on issues such as customer support, costs of manufacture, and other red flags such as long unresponsiveness timelines and lack of references. 

PCB Assembly Process-welding

When it comes to wave soldering, melted solder gets transformed to the required solder wave through an electromagnetic bump or mechanical bump that features a jet flow. 

6.1 Basic welding

Welding is the process of placing one or plenty of electronic components on a printed circuit board by use of solder. PCB welding is the same as PCB soldering. PCB soldering is dividable into fusion welding, pressure welding, and brazing. Infusion welding, heat gets applied in the form of an electric arc. In pressure welding, components get joined by the application of temperature and pressure. Lastly, brazing welding involves using a brass filler rod coated with flux to join parts of a PCB. 

A soldering process underway.jpg

6.2 Solder

Solder is a very low-melting alloy mainly used to create permanent bonds between metal workpieces. The solder gets melted to adhere and connect parts after cooling.

6.3 Welding equipment

Welding equipment used by engineers assist in creating a joint on a given workpiece. Soldering equipment includes stick welders, soldering irons, MIG welders, TIG welders, filler metals, electrodes, and torches. 

Some of the essential soldering equipment.jpg

PCB Assembly

A printed circuit board consisting of components mounted on it is an assembled printed circuit board. The manufacturing process goes by the name PCBA or printed circuit board assembly in short. 

7.1 Cost structure

•  Factors affecting assembly cost – several factors can affect the price of PCB assembly. They include thickness, the number of layers, impedance control, the weight of copper, and silkscreen color, to mention but a few.

•  Labor cost – of course, labor prices will have an impact on the overall cost of the PCB. The amount of money paid to the workforce will determine the value of the PCB.

•  Turnaround time – how fast you may want your PCBs delivered to you will also impact their prices. The reason is that the manufacturing firm may prioritize your orders first, a matter that will come with increased costs. 

•  Quantity – how many PCBs do you want? If you want a large number, then you have to be prepared for huge costs.

•  Technology – the technology used in the manufacture of PCBs will impact your PCBs’ costs. If you prefer the use of the latest technology, then you’ll pay a little extra.

•  Parts packaging – poor packaging is disastrous, especially when shipping your board. With the right PCB parts packaging, there’s no doubt that you’ll have to pay more. 

•  Material selection – the type of material that you may want on your boards, especially fire-resistant materials, may cost you more. It’s that simple. Some of the best stuff out there will cost you more. 

•  Quantity ordered – if you order more, then you’ll have to pay more. Supply will have an impact on the cost.

7.2 How to reduce the cost of PCB assembly 

There are several ways on how you can follow if you want to reduce the costs of PCB assembly. First, you need to ensure that you deliver a complete Bills of Material to your manufacturer. Secondly, ensure that you take advantage of your manufacturers’ sourcing services. Thirdly, don’t skimp on matters to do with inspection. Fourth and last, ensure that you optimize your bare board schematics. 

Prepare Printed Circuit Board Assembly Documents.

Precise assembly drawing

Before you manufacture a PCB, it’s essential to have a transparent assembly drawing that will accompany the design process. As a PCB designer, you need to know everything necessary for the drawing, such as the drilling size and special processing requirement.

Questions in the bill of materials

A measure of content is a comprehensive list of raw materials, assemblies, components, and other essential materials necessary for PCB manufacturing. The wrong BOM may see a manufacturer producing the faulty product. 

Gerber File

This is a file format that PCB designers use to get their design data. They contain information about every PCB layer that assemblers use during PCBA. Gerber files translate all the details of the PCB to the physical components of the PCB. 

Supplier list

When coming up with the bills of materials and electronics equipment schematics, PCB designers will want to improve their approved vendor list. It’s essential to improve the supply base to ensure that you are partnering with the right suppliers. 

Make sure to understand PCB documentation standard

To ensure that your PCBs are of the right quality throughout, it’s vital to ensure that you have a good understanding of PCB documentation standards. One way of achieving this is by adhering to IPC rules for the assembly of electronic equipment. With IPC standards, rest assured of coming up with high-performing PCBs. 

Files you usually forget

 As a PCB assembler, you’ll have plenty of data to use. Unfortunately, as a human being, there are some files that you may forget. To ensure that you avoid such, you have to come up with a particular folder containing essential data. For ease of access, make sure that you save such files using an available name, and probably on the desktop of your PC.

Features of high-quality files

 There are a couple of attributes that accompany high-quality files such as the bills of material, the layout format, and the schematic. Others include the assembly drawings, complete netlists, and the Gerber file. 

Inside of a PCB assembly firm.jpg

Common Problems of the Printed Circuit Board Assembly

PCBs make electronic devices that we use daily to function as intended. Therefore, when some parts malfunction on a PCB, there are high chances that the electronic device that relies on the PCB won’t work correctly. The following are some of the most common problems when it comes to PCBA. 

1. Problems that should be paid attention to between traditional PCB assembly and modern PCB assembly

Lately, things have changed, especially when it comes to the printed circuit board assembly. With technology, assemblers now employ several techniques and tools to ensure that PCB assembly is fast and precise. To find the best boards, you may have to partner with manufacturers that adhere to the latest PCB design issues such as SMT technology, wave soldering, through-hole soldering, and DFM, to mention but a few. 

2. LED problems during PCB assembly

This issue is another problem that engineers face during PCB assembly. LED points to manifest through short circuits, LED lights going off, and cases to do with open courses. You’ll get the smell of something burning or the LED light going off without warning. 

3. Too small/too large copper edges

When the copper edges of a printed circuit board are either too small or too large, it may affect its overall functionality. The minimum recommended size for outer layers must be 0.010 inches. On the other hand, the preferred format for inner layers should be 0.020 inches. 

4. Solder joint defects

As a PCB manufacturer, solder joint abnormalities is something that you’d want to avoid at all times. Weld common errors may occur due to overheated joints, cold joints, welding balling, or excessive solder use. Also, insufficient wetting, solder skips, and solder splashes could bring about weld joint defects. 

example of a defective solder joint.jpg

5. PCB assembly of small parts

The assembly of small PCB parts is a problem that many designers strive to solve. The main challenge arises, especially when a manufacturer lacks special SMT equipment. Manual placement of such small parts may produce boards that won’t function as intended. 

6. Problems with dispensing method

PCB dispensing is a process of transferring adhesive onto the printed circuit board solder mask. Dispensing ensures that all the components stay in the right place until the PCB gets wave soldered. Choosing the wrong dispensing method is another PCBA problem. Robotic distributing is one of the best-dispensing ways that you can use. 

7. Assembly of regular and irregular patches

A PCB consists of regular and uneven pieces. Some parts have to fit together while others have to stand on their own. Unfortunately, when it comes to the assembly of PCBs, many producers fail in assembling irregular pieces. More often, such needs specialized machines and expertise, and many firms lack such. 

8. Material adhesion problems during PCB assembly

Adhesion is the process of matching different types of materials to one another. High-quality adhesives are necessary during PCB assembly. The reason is that the materials are of high quality and comes with the promise of proper PCB functionality. 

9. PCB assembly process solves the heat dissipation problem

When it comes to PCBA, heat management is essential. A printed circuit board whose design cannot dissipate heat effectively will see a production of equipment that won’t operate properly. Boards that can’t dissipate heat are bound to fail in the end.

example of a defective solder joint.jpg

10. Design for Manufacturing (DFM) 

Also known as DFM, in short, design for manufacturing is an engineering practice that PCB designers use to come up with products that are easy to use. DFM examines the design of a product based on its functionality, tolerances, and materials. Before purchasing PCBs, you need to ensure that the producers had DFM considerations at the back of their minds. 

PCB Assembly Service

A printed circuit board populated with electronic parts is a printed circuit board assembly. In its free use, printed circuit board assembly (PCBA) commonly stands for “printed circuit assembly” that consist of components. 

•  PCB assembly characteristics

PCB assembly involves the entire process of connecting electronic components with the wirings of a PCB. Here, there’s the use of specialized equipment and tools required to achieve this. 

•  Parts procurement

A PCB is made of several components such as diodes, anodes, solder mask, and wires, to mention but a few. Parts procurement is necessary for PCBA. Parts procurement includes the identification of a need, the negotiation of a contract, vetting, and the selection of the best vendor. 

•  Service

This involves the selection of the best PCBA services around. There are plenty of PCBA service providers around. However, not all of them are good at their work. Service selection involves picking the best in the field. 

•  Overview of assembly capabilities

To ensure that your electronic components function correctly, you may have to source or use PCBs manufactured by firms with impressive assembly capabilities. Is the firm of your choice able to do conformal coating and potting? What about knowledge in PTH technology? Ensure that you work with a firm equipped in automated solder paste application, automatic optical inspection, and SMT reflow or wave soldering.

•  Assembly equipment

The type of assembly equipment matters a lot. Standard or substandard assembly equipment may see you producing PCBs that aren’t fit for the market. As a manufacturer, you need to ensure that you use state-of-the-art equipment that produces high-quality PCBs. 

•  Quality Assurance

As a printed circuit board assembler, you need to ensure that you maintain the desired level of quality for your products. You can achieve this by paying particular attention to every stage of the manufacturing process.

An engineer inspecting aboard after the final assembly.jpg

Summary

Your printed circuit boards will function properly in your electrical components if you get to understand all the above aspects. Your printed circuit boards will function properly in your electrical components if you get to understand all the above elements. If you need more information about PCB assembly, you can contact us. We have a professional PCB production factory here, if you are interested, you can visit it. I hope this article is helpful to you.

Hommer
Hi, I am Hommer, the founder of WellPCB. So far we have more than 4,000 customers worldwide. Any questions you can feel free to contact me. Thanks in advance.

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