The PCB assembly process is complex and multi-faceted. It requires a plethora of tools and equipment. It requires highly specialized PCBA equipment. There are PCB kits that can assist you in creating your very own DIY PCBs at home. However, this should never trick you into believing that mass-producing high-quality circuit boards for commercial electronic products are accessible. This guide will explore all the equipment involved in the printed circuit board assembly and fabrication process.
What is PCB Assembly Equipment?
Female engineer checking circuit board design in factory
PCB assembly equipment describes the tools, apparatuses, instruments, and appliances we use to assemble printed circuit boards after we fabricate them. Since the PCB assembly process has different stages, each stage requires a unique set of instruments to execute correctly. These stages or their order may differ from manufacturer to manufacturer. However, in most cases, the PCB assembly process requires them to produce effective circuit boards.
The Four Stages of The PCB Assembly Process
Printed circuit board without electronic components ready for the assembly process
The four main stages of the PCB assembly process are:
- Paste Application
- Automated component placement
PCBA Equipment: Paste Application
The manufacturer will apply solder paste to the board during the paste application process. The equipment involved in the paste application stage are:
Automatic Stencil Printer
PCB design kit including stencil
In most cases, the assembly company will require a PCB or SMT stencil to apply the solder paste efficiently. The stencil comprises stainless steel. Modern PCB assembly companies use an automatic stencil printer with a laser cutting attachment to create the stencil. Moreover, this machine receives instructions from a computer running CAD software. Once we've manually inspected the stencil and are satisfied with it, we can apply solder paste.
Solder Paste Printing Machine
PCB conductive paste screen printer
The solder paste printing machine is responsible for dispensing solder paste evenly on the PCB. Either an operator or the device itself (automated) will lock a stencil onto the PCB. Next, the machine will dispense a precise solder on the pads.
The solder paste printing machine will then use a blade to spread and assert the paste into specified regions of the PCB. These regions are where the next stage will place the PCB's components. Nevertheless, after we complete this process, we will need to inspect the application of the solder paste to avoid any soldering issues.
Solder Paste Inspection (SPI) Machine
3D SPI machine
The solder paste inspection machine helps the manufacturer assess the precision and quality of the paste application process. These machines can be very advanced. They can detect the solder placement's volume, height, and area. Additionally, they can capture 2D and 3D images of solder deposits and compare them against the stencil. If the solder paste inspection machine detects any issues with the solder paste, the manufacturer will have to rework the solder paste application. Contrastingly, if it doesn't, the board can move to the next stage of the PCBA process.
PCBA Equipment: Automated Component Placement
PCB being assembled on the pick and place machine
The manufacturer will prepare the components (and the PCB) during the mechanical component placement stage before placing them on the PCB. The most common PCBA equipment involved in this stage include:
Glue Dispensing Machine
Some manufacturers may skip this process because the solder paste may be enough to form a temporary bond between the PCB and its components. However, applying glue may be very important if the manufacturer uses wave soldering. It is because the impact from the wave may displace the members.
Nevertheless, the automated glue dispensing machine will apply an adhesive mixture to the PCB. This process will create a temporary bond between the PCB and its components before reaching the final soldering process.
Close-up of Pick-and-place machine in a robotics factory
Before the advent of the pick-and-place machine, human workers would arrange the components on a PCB by hand. For smaller pieces, this would require a pair of tweezers.
The pick-and-place machine automates this process by gathering components and precisely placing them on the PCB. These machines are high-speed and accurate. As such, they can place up to 3000 pieces per hour. Once the pick-and-place device has situated all the necessary components on the PCB, it can move on to the following assembly process.
Automatic pick and place machine for SMD components
PCBA Equipment: Soldering
The two most popular soldering techniques for high-frequency PCB assembly are wave and reflow soldering. This process involves solder, solder flux, a soldering iron/gun, and a soldering station. For smaller high-precision productions, the manufacturer may still use manual soldering.
Nevertheless, manufacturers responsible for large production use one of two types of equipment, depending on the method they've opted to use.
Reflow Soldering Machine
Reflow oven/soldering machine
The Reflow soldering is still the most popular soldering technique for PCB assembly. Thus, you'll find reflow soldering machines in most PCB factories. Nevertheless, the reflow soldering machine consists of a tunnel-like oven with a conveyor belt.
It will heat the PCB in a controlled manner. This process ensures that the previously applied solder paste softens and hardens, creating a reliable bond between the PCB and its components.
Wave Soldering Machine
Wave soldering machine
Source: Wikimedia Commons
The first phase of a wave soldering machine's function is cleaning. It will apply a flux layer to purify all the component pads and contacts. Thus, this process will ensure that the wave soldering process creates efficient bonds.
Next, the PCB goes through a preheating process to prevent thermal shock, resulting in the corruption of the PCB's materials. Once this phase is complete, the PCB passes over a wave of molten solder. Incidentally, the underside of the PCB will come into contact with this wave. This process will allow the components' leads to bond to their assigned pads and holes.
PCBA Equipment: Inspection
Electronic workshop and testing Equipment
Manual visual inspection is not enough. PCB testing is an essential facet of the assembly process. Thus, each PCB test technique requires its own set of tools and test equipment.
In-Circuit Test System
A system consisting of various instruments is a part of a large singular machine. Usually, you can often locate the in-circuit tester at the end of the manufacturing line along with the functional tester. The in-circuit tester/test system will detect any defects from the manufacturing process. Thus, it will reduce the amount of rework the board will require at the functional test station.
Depending on the capabilities of the in-circuit test system, a machine or operator will place the PCB in a fixture. Next, a computer will start analyzing the board after an automatic or manual instruction initiates it. During this process, it will display a list of results. It will do this until it reaches a final result and flashes it as a pass or fail message.
From top to bottom, the tester consists of a
- Fixture wires
- Fixture interface pins
- Module interface pins
- Tester pin card
- Test head.
The module interface pins (located on top of the tester pin card) connect to the fixture interface pins. These pins then use wires to connect to the probes. The probes will then connect to the PCB when an operator places it into the fixture. Ultimately, this interface allows signals to flow between the tester and the board.
Flying Probe Test Machine
Flying probe test machine
Instead of a fixture, the flying test probe machine uses a mobile probe to detect faults in the PCB. It works on the same principle as the in-circuit test system. However, it's more flexible and cheaper to implement.
Electronics workshop assembly and testing station
Functional tests typically occur after the ICT or probe test. Nevertheless, we either use an electronic device containing the PCB after production or use equipment that emulates it. Since the purpose of the FCT is to ensure that the PCB functions correctly under regular operation, we must power the PCB. Incidentally, we require instruments and tools to allow us to do so.
An open temperature and climate test chamber for PCB aging tests
In the aging test (or thermal aging test), the PCB is run for an extended period under elevated temperatures. Thus, the equipment we use during this test must power the PCB and simulate increased temperatures and humidity. Additionally, testing must follow the ECIA - EIA-364-17 standard. Often, a manufacturer will utilize an aging or burn-in tester to accommodate multiple PCBs simultaneously. This fact is important because the aging test may take a considerable amount of time. Therefore, the more boards you can test, the more efficient testing is for mass production.
Robotic system for verification of PCBs
The AOI tester consists of a computer, an interface, and a conveyor belt. For large productions, the entire process may be automatic. However, most shows require an operator to place the PCB on the conveyor line so that the interface can process it. Nevertheless, often the operator will supervise the inspection. The interface contains a high-resolution camera that captures images of the test PCB. It feeds these images to a computer that compares them to a template. If there are no issues with the PCBA's structure, the computer will display a 'PASS.' However, if it finds any faults, it will display a 'FAIL' and alert the operator.
In principle, the AXI tester functions similarly to the AOI tester, requiring an operator to supervise it. However, the AXI tester's structure differs because it must have a container or shield to protect workers from radiation. Often, the AXI tester uses a more powerful computer with more sophisticated software.
A good AXI solution must be capable of revealing the 2D, 3D, and computerized tomography of a PCB's structure. These capabilities give operators complete control. Additionally, they allow them to view and analyze suspect areas from any angle.
Picking The Right PCB Assembly by Equipment and Capability
A set of circuit boards stacked in front of each other
Yes, the PCB fabrication process is essential. However, you want to collaborate with a company that will verify the integrity of your designs and construct the best PCBs. The best PCB manufacturers have the latest equipment that complies with your requirements and the latest industry standards. These specifications may include PCB prototyping and a thorough final product inspection. OurPCB is an industry leader with the newest PCBA equipment to meet these requirements and ensure production efficiency.
With OurPCB, you can't go wrong. Moreover, we offer these services at a reasonable price. Don't hesitate, contact us today.