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What is the PCBA Manufacturing Process?

PCBA manufacturing
PCBONLINE Team Thur, Feb 25, 2021

PCBA manufacturing is the process of having blank printed circuit boards assembled. You can get an insight into the PCBA manufacturing process at the PCB factory below.

PCBA Samples Manufacturing Process

Before large-scale PCBA manufacturing, the complete PCBA samples should be manufactured to see if all the steps and details are flawless.

  • Step 1. Check Bill of Materials (BOM) and Gerber Files

A BOM is an Excel containing all your components' requirements. Responsible PCB companies usually check your BOM and Gerber files to make sure there are no problems in your designs before giving you a quote.

Not all assembly companies check your BOM and this may lead to failures. But PCBONLINE does. An experienced engineer checks your board design, component samples, and your BOM carefully. If everything is okay, the assembly starts.

bill of materials

  • Step 2. Manufacturing PCB and SMT Stencils for PCB Assembly

If you are ordering one-stop PCB assembly, the PCB company will manufacture the PCBs. During PCB manufacturing, the SMT stencils for PCB assembly are also manufactured. PCB manufacturing takes time, and how long it takes depends on the circuit boards' complexity. At PCBONLINE, the shortest manufacturing period for PCB prototypes is 12 hours.

PCB companies do not manufacture but source electronic components. Currently, shortly, some components like ICs are in short supply. Please prepare these rare components before PCB assembly.
  • Step 3. PCBA First Article Test

The first article test (FAT) is necessary for mass PCBA production because if minor mistakes happen, the whole large batch of PCBA becomes a failure. Usually, the PCBA factory manufactures 5 PCBAs and picks up one of them randomly for the test.

A technician uses the probe to touch every device on the PCBA, the FAT machine receives and analyzes the returned data such as resistance and voltages, and the computer shows the test results visually and auditorily. If the PCBA is good, the computer says "correct". Not Good, it says "wrong".

After the FAT, a test report is generated for the client to review. If the client thinks the manufacturing is good and approves batch PCBA manufacturing, then the PCBA manufacturer starts batch production.

first article inspection

Complete Process of Batch PCBA Manufacturing

Below is the complete process of large-scale PCBA manufacturing.

  • Step 1. Solder Paste Printing

The circuit boards go through the SMT machine one by one. In the SMT machine, an SMT stencil is set up, and the PCB is at the bottom of the stencil. The SMT machine's blade carrying the solder paste presses the PCB stencil, and the solder paste goes through the stencil holes to paste on the PCB pads. when the circuit board is pasted, it leaves the SMT machine and the next board goes into the machine.

solder paster printing

  • Step 2. Solder Paste Inspection (SPI)
  • solder paste inspection

Standard solder paste thickness ranges from 0.09mm to 0.15mm, and the solder paste must cover the PCB pads completely. The PCB comes in the SPI machine, and the machine detects if the solder paste thickness and shape are qualified for PCB assembly.

  • Step 3. High-Speed Mounting

When the PCB goes into the high-speed mounter, SMD components in smaller sizes are picked and placed on the desired PCB pads by a robot at an extremely high speed. These SMDs' package sizes are 0201, 0402, and 0603, such as deductors, resistors, and capacitors. When the high-speed mounting machine completes the set-up operations, the PCB mounted with SMDs leaves from the high-speed mounter, and the next bare PCB comes in.

high speed mounter

  • Step 4. Functional Mounting

Larger SMD components are in the package size of 0804 and above, such as BGAs, FPGAs, ICs, USBs, etc. Like in the high-speed mounter, these SMDs are also prepared before PCBA manufacturing. In the functional mounter, a robot picks and places the SMDs on the required pads according to the set-up program, but the operation speed is much slower and more accurate. Then the PCBA leaves the functional mounter. it has to pass the solder paste inspection (SPI) to make sure the solder paste thickness and shape on the pads are qualified.

functional mounter

  • Step 5. X-Ray

When all the SMDs are mounted, the PCBA goes through the X-ray test. The X-ray penetrates the PCBA and generates an image on the machine screen. Technicians judge if the PCBA is qualified from the test results.

  • Step 6. Reflow Soldering

In this step, the PCBAs pass the reflow soldering oven, and the solder paste melts and solidifies. A reflow soldering oven has different temperature zones, and the temperatures are controlled. Usually, in the first temperature zones, the PCBAs are pre-heated. In the middle, the solder paste melts completely. In the send temperature zones, the solder paste gradually cools down and solidifies. After reflow soldering, the SMDs are soldered to the PCB pads tightly.

If you require lead-free PCB assembly, remember to ask about the PCBA manufacturer's reflow oven capabilities. Lead-free PCB assembly requires 20°C higher temperatures for reflow soldering than lead-containing assembly. At PCBONLINE, our reflow ovens have ten temperature zones and can reflow solder lead-free PCBs. The PCB assembly companies whose reflow ovens have eight temperature zones can manufacture only lead-containing PCBAs.

reflow soldering oven

  • Step 7. Automatic Optical Inspection (AOI)
  • AOI

After reflow soldering, the PCBAs have to go through the AOI machine. A camera automatically scans the PCBA. The AOI machine collects images, compares the tested solder joints with the set-up parameters in the database, checks out the defects on the PCB by image processing, and marks the defects on the screen. If there are defects, a quality control technician marks the defects on the circuit boards for maintenance.

The above is the automatic SMT assembly, and below is the THT assembly line. THT assembly is done manually.

  • Step 8. Through-hole (PTH) Assembly

PTH assembly is the process of mounting PTH components on PCBAs. PTH components have much longer pins than SMDs, and the pins have to go through the PCB through holes. This operation is quite simple and is usually done manually.

PTH PCB ssembly

  • Step 9. Wave Soldering

After the PTHT assembly, there is still space between the PTH pins and the PCBA, and wave soldering fills the space and connects the PTH components tightly to the PCBA.

The PCBAs go through a pre-heater to warm up and then go through the wave soldering oven. In the oven, the liquid tin fills the space between the PTH pins and the PCBA. When the PCBA leaves the oven, the tin cools down and solidifies. In this way, the PTH components are connected firmly to the PCBA.

wave soldering machine

  • Step 10. Trim PTH Pins and Fix PCBA

    touch-up PCBA

In this step, first, a technician trims the PTH legs to be 1 to 2mm long. The other technician uses a soldering iron to fix the PCBA if anywhere is not soldered perfectly.

  • Step 11. Conformal Coating

This step is optional. Conformal coating is sprayed on the PCBA surface automatically, and it protects the PCBA from moisture, dust, chemicals, vibration, etc.

  • Step 12. PCBA Functional Testing (FCT)

A technician picks up the PCBA on the FCT jig and powers it on. The functional tester tests the current, voltage, and so on. The test results are displayed on the computer screen.

During PCBA manufacturing, PCBA testings, such as SPI, AOI, and visual inspection, are necessary in case of soldering defects to avoid economic losses due to re-assembly. At PCBONLINE, functional testing is free for customers.

functional test

  • Step 13. Thermal Aging Test

The PCBAs are put in a thermal chamber to power on for about 250 hours without interruption. The temperatures are elevated to a certain level. All the PCBAs should follow the ECIA - EIA-364-17 standard.

thermal aging test

Other PCBA tests can be added to the above steps of PCB assembly. For the PCBs used for aerospace, defense, automotive, medical, and communications, four-terminal sensing is also required for PCBA manufacturing. Besides, the flying probe test, in-circuit test, IC programming, repairing if there's any problem, and so on may also occur depending on the practical needs.

The above step-by-step process is rigid PCBA manufacturing. PCBONLINE also provides flexible PCB assembly.

Why PCBONLINE is a Reliable PCBA Manufacturer

If you're looking for batch PCBA manufacturing, you need to work with a reliable PCB assembler. PCBONLINE, a leading one-stop PCB manufacturer for medical, aerospace, defense, automotive, industrial, communications, and consumer electronics, is recommended for PCBA manufacturing.

Reasons to choose PCBONLINE for PCBA manufacturing:

    • PCBA manufacturing of any quantity at PCBONLINE follows the IPC-A-610 Class 2/3 standards.
    • PCBONLINE applies Kelvin's four-terminal sensing, conformal coating, and functional tests to PCBA manufacturing.
    • Solution experts provide one-on-one engineering support and DFX.
    • Solution experts always seek to save clients' costs with the latest technologies and PCBA manufacturing optimization.
    • For $5,000+ orders, complete PCBA samples and functional tests for PCBA manufacturing are free.

PCBONLINE provides EMS PCBA manufacturing, including SMT assembly, THT assembly, value-added services, and box-build assembly. You can register for free and get a quote online, or contact info@pcbonline.com for a quotation.


This article tells what is going on in PCBA manufacturing. Different PCBs have different requirements for assembly. The above steps are almost the complete PCBA manufacturing process. To get to know more about PCBA manufacturing, welcome to contact PCBONLINE.


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