What is the PCBA Manufacturing Process?

Printed circuit boards (PCBs) are a crucial component of modern electronics. PCBs are a miraculous development that has allowed for the expansion of virtually every type of electrical device. A printed circuit board (PCB) is a medium for conducting electricity along its copper tracks. PCBA, or printed circuit board assembly, is the procedure by which electronic components are soldered to a printed circuit board. We use different manual and automatic tools for the process of PCBA manufacturing.

Manufacturing Procedures for PCB Samples

Prior to large-scale PCBA manufacturing, it is essential to complete the PCBA samples’ manufacturing, the steps of which are elucidated below –

• Take a look at the BOM and files (Gerber)

A BOM or the bill of materials is merely an Excel sheet detailing all the necessary components. The most telling feature of a reliable PCB manufacturer is that they inspect your Bill of Materials and Gerber files before providing an estimate. However, it is noteworthy to remember that not all PCB assembly companies look through the BOM, which may culminate in failures.

• The fabrication of SMT stencils for use in the printed circuit board and PCB assembly

When you request turnkey PCB fabrication services, the PCB manufacturer handles every step of the process for you. PCBs and the necessary SMT stencils for assembly are manufactured simultaneously. The time needed to fabricate a printed circuit board (PCB) is proportional to the circuit board’s degree of complexity. It would help if you kept in mind that not all PCB companies manufacture source electronic components. Currently and in the near future, some components like ICs are in short supply. Thus, you should prepare these rare components before PCB assembly.

• PCBA First Article Test (FAT)

The first article test (FAT) is critical for mass PCBA production because if a minor glitch happens, the entire batch of PCBA becomes a failure. Therefore, under normal circumstances, the PCBA factory manufactures five PCBAs and picks up one of them randomly for a thorough examination. 

Firstly, a technician uses the probe on every device on the PCBA; the FAT machine gets and scrutinizes the returned data, such as resistance and voltages. Ultimately, the computer displays the test results visually and auditorily. So, if the PCBA is in appropriate condition, the computer says ‘correct,’ and if it is not suitable, then the computer says ‘wrong.’

After the FAT, a test report is created for the client to review. Production of the PCBAs will begin once the client has reviewed and approved the batch manufacturing.

Complete Process of Batch PCBA Manufacturing

Mentioned below are the steps entailed in large-scale PCBA manufacturing –

Step 1: Solder Paste Printing

Each individual circuit board is fed into the SMT machine at the outset. The PCB is at the stencil’s base in the SMT machine, where an SMT stencil has been set up. After that, the PCB stencil is pressed down on by the SMT machine, and the solder paste is forced through the holes in the stencil and onto the pads of the PCB. After the circuit board has been pasted, it is removed from the SMT machine and replaced with a new board.

Step 2: Solder Paste Inspection

Solder paste must completely cover the PCB pads, with a typical thickness ranging from 0.09 mm to 0.15 mm. The PCB comes in the SPI machine, and the machine detects the solder paste thickness and is good enough for PCB assembly.

Step 3: High-Speed Mounting

The third step in batch PCB manufacturing is high-speed mounting. When the PCB goes into the high-speed mounter, the SMD components of smaller sizes are picked up on the desired PCB pad by a robot at an incredibly high speed. The SMD packages’ sizes are 0201, 0402, and 0603, including deductors, resistors, and capacitors. When the high-speed mounting device finishes the setup operation, The PCBs mounted with the SMDs leave the mounting device, and the next PCB comes in.

Step 4: Functional Mounting

ICs, USBs, BGAs, and other similar components are all examples of the bigger SMD components that come in package sizes of 0904 and above. These SMDs are likewise picked and placed on the appropriate pads according to the program settings, just like the high-speed mounter. The speed of operations is slower and more precise, however. The PCBA is then removed from the functional mounter. The first step is to have it go through solder paste inspection (SPI), which checks the glue thickness and pad form to make sure they are up to snuff before assembly and manufacturing can continue.

Step 5: X-Ray

After the SMDs are mounted, the PCBA goes through the X-Ray test. X-rays penetrate the PCBA and generate an image on the machine screen, which technicians judge.

Step 6: Reflow Solution

In the sixth stage, known as the reflow solution, the PCBAs are heated in a reflow soldering oven, where the solder paste melts and hardens. A reflow soldering oven has various temperature sections and controls. Usually, PCBAs are pre-heated in the first temperature zones, then the solder paste melts in the middle section, and so forth. After the reflow soldering, the SMDs are tightly soldered to the PCB pads.

Step 7: Automatic Optical Inspection (AOI)

The AOI machine inspects the PCBAs once the reflow soldering process is complete. The PCBA is scanned by a camera, and the AOI machine collects photos, compares the checked solder connections with the setup parameters in the database, examines the defects on the PCB by image analysis, and flags the hiccups on the circuitry for upkeep based on the results.

Step 8: Through-hole Assembly

PTH assembly, or through-hole assembly, is the method used to attach PTH components on printed circuit boards (PCBs). PTH components’ pins are substantially longer than those of SMDs; hence they must pass through holes in the PCB. It’s a straightforward process that’s typically completed by hand.

Step 9: Wave Soldering

After the through-hole assembly, gaps still exist in the PTH pins and the PCBA. Wave soldering eliminates all gaps and securely joins the PTH parts to the PCB. After being preheated, the PCBAs return to the soldering oven for a second round. The PTH pins and PCBA are filled with liquid tin while the assembly is baked. As soon as the PCBA is taken out of the oven, the tin begins to cool and solidify. Because of this, the PTH parts are securely attached to the PCBA.

Step 10: Fix PCB and Trim PTH Pins

The tenth step includes a technician trimming the PTH legs to be 1 to 2 mm long. The second technician then inspects the PCBA and, using a soldering iron, fixes any areas where the soldering is inadequate.

Step 11: Conformal Coating

When moisture, dust, vibration, chemicals, etc., pose a threat to a PCBA, a conformal coating can be sprayed on the surface.

Step 12: PCBA Functional Testing (FCT)

The penultimate step includes a technician picking up the PCBA on the FCT jig and powering it on. The functional tester tests the current, voltage, and likewise. Finally, the test results are shown on the screen.

Step 13: Thermal Aging Test

The final step in PCBA production is to run the batches in an uninterrupted thermal chamber for about 250 hours. The heat is turned up to an exact degree. The ECIA-EIA-364-17 standard must be met by all PCBAs in the market.

Why Absolute PCB is a Reliable PCBA Manufacturer

Absolute PCB is one of the top-tier PCB assembling and manufacturing companies catering to the needs of diverse industries, such as defense, automobile, communications, medicine, and likewise.