The Comprehensive Guide to PCB Assembly Process at JLCPCB: Efficient and Reliable PCB Manufacturing

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.  JLCPCB provides PCB Assembly by taking charge of the full steps of soldering each component to its placement on the board based on their capabilities which shortens the path for engineers and companies by saving more time.

The PCB Assembly process comes directly after the PCB manufacturing and by sweeping away the necessary amount of solder paste on the component’s 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.

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 12 pm PST, the assembly lead time starts the next business day. Materials received after  12 pm 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 ensure 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.

Steps involved in the 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

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 electronic 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 during the PCB manufacturing but also the Stencil preparation as well, this is another step executed in parallel to the parts preparation and PCB manufacturing. A Stencil is the key to dropping 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 swept 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 with 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 position 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.

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).

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.

JLCPCB is dedicated to making tech innovation more accessible. By leveraging an intelligent management system, cutting-edge equipment, and large-scale manufacturing, we offer top-quality products at unbeatable prices, ensuring budget constraints don't hinder electronic engineers and makers. 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!