Printed Circuit Board Assembly (PCBA): A Step-by-Step Guide

One of the most important factors to create a working circuit board is the assembly technique and process, such a step has to be controlled and carefully executed to ensure the wellness of the final produced device. Printed Circuit Board Assembly (PCBA) is the process of assembling electronic components onto a printed circuit board (PCB) to create a functional electronic device. The assembly process involves various stages, from placing components on the board to testing the final product. This guide provides a comprehensive overview of the PCBA process, highlighting each critical step to ensure a successful and reliable assembly.

JLCPCB provides PCB Assembly by taking in charge the full steps of soldering each component to its placement on the board based on their capabilities which shorten the path for engineers and companies by saving more time for them. The PCB Assembly process comes directly after the PCB manufacturing and by sweeping away the necessary amount of solder paste on the components exposed pads then placing the components for the next step which is the Reflow to accomplish the circuit assembly. We've provided a comprehensive guide on PCB manufacturing, which you can check out from here.

PCB Assembly at JLCPCB:

The JLCPCB PCB Assembly service is a reliable yet efficient option for customers to satisfy their electronics manufacturing needs, by offering a high-quality assembly for a judicious price, such PCBA service is at the top of the list for every engineer's choice.

The more assembly insurance leads to more effectiveness of circuit boards, that’s the main reason behind the PCB Assembly success around JLCPCB PCBA service. Every manufacturing step is thoroughly treated by knowledgeable and qualified staff.

Flow of JLCPCB PCB Assembly Process:

1. Our team confirms the necessary files and order details.

2. Manufacture SMT stencil (if needed).

3. Program our machines from the BOM and Centroid file, before the materials arrive. Discrepancies found in the files will be addressed.

4. After all the materials are received, our team performs a kit audit of the materials. Discrepancies or additional questions will be addressed. Before the assembly lead time begins we must have all questions answered.

5. If all materials are in before 12pm PST, the assembly lead time starts the next business day. Materials received after 12pm PST will be considered received on the next business day. The reason for this is to allow proper time for the materials to go through the kit audit process.

6. The SMT components are assembled first with our automated equipment. The first board goes through extensive QA to assure part placement and polarity are correct. The boards are then inspected (visually and with an AOI machine) as they come off the reflow oven.

7. BGA components are X-rayed to verify placement accuracy and to detect any solder bridges.

8. After SMT the boards are washed when applicable.

9. Thru-hole components are inserted and soldered by hand or with a selective soldering machine depending on the quantity and board design.

10. After thru-hole boards are washed again when applicable.

11. A final quality inspection is performed.

12. The finished PC board assemblies and all extra materials are prepped for packaging.

What are the Files Required For a PCB Assembly Order?

• Gerber file, it is used for PCB production.
• BOM file(Bill of Materials). View Sample BOM.
• CPL file(Component Placement List / Pick & Place File (PNP) file), it is used by our automated SMT Assembly machines to determine where each part should be located on the board. View Sample CPL.

What Information is Contained in these Assembly Files?

Gerber Files: PCB layout file which includes all the layers (copper, solder mask, silkscreen, solder paste, etc.

Component pick and place file (CPL file): This file contains component locations, rotations and reference designators.

Bill of Materials (BOM): In Excel format. Your BOM should include:

• Reference designators
• Quantity of each part
• Manufacturer part number
• Part description
• Type (SMT, Thru-Hole, Fine-pitch, BGA, etc.).
• Package description (QFN32, SOIC, 0805, etc. package is very helpful but not required).

If designing the files in EasyEDA then it automatically produces a JLCPCB assembly supported file.

Steps involved in PCB Fabrication Process:

Step 1 –  Parts preparation

Step 2 – Solder Paste Application

Step 3 – Solder Paste Inspection (SPI)

Step 4 – Components Pick and Place

Step 5 – Reflow Soldering

Step 6 – Assembly Inspection

Step 7 – Final Testing and Validation

Step 8 – Final Assembly and Packaging

1- Parts Preparation:

As soon as the customer uploads the PCB design files, the JLCPCB engineers arrange the related “data for manufacturing” and release the electronics components required for assembly.  The parts to be loaded later to the assembly pick and place machine feeders. The assembly includes all the parts available in the JLCPCB parts library which covers the Surface Mounted Devices (SMD) and the Through-Hole (THT) components as well. The customers could select their parts through the JLCPCB library.

where they can search the needed components through the very well-arranged parts categories that sort more than 350K components. The parts are recognized automatically through the Assembly system based on the customer’s provided “Bill Of Materials” file. All the needed information for each part like the part Prefix and quantity, are prepared and wait for the PCB manufacturing step.

2- Solder Paste Application:

The faster we go the faster we deliver, not only the parts should be prepared while the PCB manufacturing but also the Stencil preparation as well, this is another step executed in parallel to the parts preparation and PCB manufacturing. Stencil is the key to drop the exact amount of solder paste on each component’s pad. The applied Solder paste covers the spots of the exposed pads after getting the solder paste sweeped on the Stencil.

JLCPCB uses a fully automated process for solder paste deposit and inspection, as soon as the PCB gets ready out of the PCB manufacturing process it is then directly transferred to receive the solder paste through the exposed pads on top of the Stencil.

3- Solder Paste Inspection (SPI):

Since each step requires careful supervision, the solder paste application is verified through the SPI (Solder Paste Inspection) process. This process assesses the quantity of solder paste deposited on the PCBs, ensuring that every component pad receives the necessary amount of paste for proper connections. This crucial inspection step helps to prevent incorrect assembly, which could otherwise lead to circuit board malfunctions. By detecting potential issues early in the assembly process, SPI ensures the overall reliability of the final product.

JLCPCB uses fully automated machines for the inspection through its Automated Optical Inspection (AOI) and its advanced X-Ray high-definition cameras. Which determines the solder paste geometry on the pads and decides the Good and Bad execution of the SPI by

capturing and comparing real time images with reference design.  This inspection will certainly help to create a successfully assembled circuit board equipped by properly connected components with a durable electrical connection.

4- Components Pick and Place

Once the solder paste is applied to the designated areas, the components are carefully placed using advanced machines known as Pick and Place (P&P) machines. This process is highly precise and swift, allowing for the rapid and accurate placement of components in the shortest possible time. The machine is first loaded with components through its many feeders that could receive parts reels, tubes or even waffle packs. Heads of the machine arm move to take the parts and lay them on the PCB, those heads could take parts of several packages (small and big parts).

The machine knows where to positionate the arm to exactly match the correct part position on the board; these moves are performed through a program that defines the X and Y centre position of the components. This program is manually created by JLCPCB engineers based on the “Pick and Place” file provided by the customer. See the process through in factory video.

5- Reflow Soldering

This is the most widely commonly used process for all PCB manufacturers to attach surface mounted components to circuit boards. JLCPCB uses the appropriate reflow soldering machine equipped with a suitable Oven capable of assembling several board sizes and helps to achieve the required line speed.

The quality of a well-assembled part is heavily dependent on the assembly process itself. Even with the right machinery, additional requirements must be met to ensure proper soldering of the components. The primary goal is to create reliable solder joints by pre-heating the components, PCB, and solder paste, then melting the solder using an optimal reflow profile that avoids damage from overheating.

6- Assembly Inspection

This is an additional layer of quality assurance in the assembly process. After the components are soldered to the PCB, it's essential to verify that all parts are properly attached and free from issues like misalignment, cold joints, or short circuits between pads. An optical camera is used for this inspection to distinguish between good and defective parts. The assembly status is judged by comparing the inspected parts against an ideal reference image provided by JLCPCB engineers.

In some specific cases where the camera could not spot the pads then the X-Ray inspection machine is used to check the assembly especially for components where the pads are hidden underneath the component’s hood (for BGA package). Common inspection techniques include:

• Automated Optical Inspection(AOI): AOI machines use cameras to scan the PCB and detect defects such as missing components, misalignments, or soldering issues.

• X-Ray Inspection: For boards with complex or dense components, X-ray inspection can reveal hidden defects like voids or insufficient solder in BGA (ball grid array) packages.

• Manual Inspection: Trained technicians visually inspect the PCB under magnification to catch any issues missed by automated systems.

Any defects identified during inspection are addressed through rework, where necessary corrections are made, such as resoldering components or replacing faulty parts.

7- Final Testing and Validation

Once the PCB assembly is complete, the board undergoes a series of tests to verify its functionality and performance. Common tests include:

1. In-Circuit Testing (ICT): ICT checks the electrical connections, component values, and circuit continuity on the assembled PCB.

2. Functional Testing: This test simulates the PCB’s operation in its intended application, ensuring that it performs as expected under real-world conditions.

3. Burn-In Testing: For high-reliability applications, burn-in testing subjects the PCB to extended periods of operation at elevated temperatures to identify early failures.

Passing these tests is crucial for ensuring that the PCB meets all specifications and operates reliably in the final product.

8- Final Assembly and Packaging

After successful testing, the PCB is ready for final assembly and packaging. This may involve mounting the PCB into its enclosure, connecting it to other assemblies, or integrating it into a larger system. The final product is then packaged, labelled, and prepared for shipment.

Get your Hands on PCB Assembly Service in Just 3 Steps:

We have a specialized fully automated PCB assembly lane that deals in small-volume (2 pcs) to as high as 80K pcs. With our networking sites EasyEDA, LCSC we provide a one-stop solution from PCB designing to fabrication and assembly. Follow the following steps to order your first PCBA:

Upload : Upload your Gerber, BOM & CPL files to get an instant quote on PCB.

Select: Select the parts and components to be placed for assembly. Assembly Prices start at $8.00 setup fee, and a minimal assembly fee of $0.0017 per joint.

Receive: A streamlined process from ordering, sourcing parts and PCB prototyping allowing you to iterate, improve and deliver on time.

Conclusion:

Printed Circuit Board Assembly (PCBA) is a complex and multi-step process that requires precision, quality control, and expertise. From design and component placement to soldering and testing, each stage plays a crucial role in ensuring the reliability and functionality of the final product. Whether you’re a hobbyist assembling a small project or a manufacturer producing high volumes of electronic devices, understanding the PCBA process is key to achieving successful outcomes. With the right tools, techniques, and attention to detail, you can create high-quality PCB assemblies that meet the demands of today's advanced electronics.

After getting the boards very well assembled and fully inspected and tested, those produced circuit boards are then cleaned and delivered to JLCPCB customers. At a glance, the assembly process might appear straightforward, but it involves many intricate steps that must be carefully executed to produce a durable, functional circuit board at a competitive price. To further support your creativity, we're offering $80 in new user coupons. Sign up on the JLCPCB official website and start bringing your ideas to life with us!