For easier nomenclature, acronyms are often used in electronics manufacturing to shorten frequently used words and phrases. Take the example of “PCB” and “PCBA” which seem to sound the same and synonymous, but in fact are two different technical terms. You probably have come across these terms when talking about electronics manufacturing. PCB and PCBA are often used interchangeably despite having different meanings, PCB can be PCB bare board and PCBA (PCB with components), while PCBA usually only means PCBs with electronics components.
What is PCB and PCBA? PCB is short for “Printed Circuit Board” and PCBA is short for “Printed Circuit Board Assembly”, the only difference is with or without “Assembly”. Based on these meanings, you will see that the only similarity is the term Printed Circuit Board, which is basically the physical board, sometimes referred to as “substrate”, since it is the structure for holding electronic components. On the other hand, Printed Circuit Board Assembly or PCBA, is already a combination of the PCB and the mounted electronic components, thus PCBA has more assembly steps than the PCB. So, PCB just means a circuit board with traces, drill, pads which make electrical connections. But only with electronic components assemblies on the PCB can achieve functions and make the circuit board live, and we call this process PCBA (PCB assembly).
Let’s further explore beyond the meanings of these two terms and some familiar misconceptions by grasping the key differences between PCB and PCBA based on the following aspects:
- Composition and Function
- Process Flow and Machines
- Manufacturing Defects
- Production Time
Composition and Function
PCBA and PCB have different compositions and functions. A PCB consists of the dielectric substrate, copper foil, prepreg or bonding materials and solder mask. The laminates can be FR4 which is a flame-resistant (thus the abbreviation FR) fiberglass-reinforced epoxy, or a PTFE for high frequency applications. The PCB also acts as a medium for heat transfer, also technically called a “heatsink” which is critical for power applications and high reliability electronics.
A PCBA is made of the PCB, electronic components such as resistors, transistors, and capacitors and solder material to bond the component. PCBA provides the connection in the circuitry and acts as hardware support for the electronic devices.
Process Flow and Machines
The processes and machines used in PCBA and PCB are different. The general processes of PCB fabrication can be simplified as follows: Film generation, etching, plating, solder mask, screen print, drilling, inspection, and test. These processes can be enhanced or changed based on the fabricators’ manufacturing design.
- During film generation, the image of the board is generated from the Gerber files which is the basis for the PCB manufacturer.
- Etching process removes unwanted copper to come up with the desired circuit pattern. The remaining copper is protected by a hardened photoresist.
- Holes drilling, holes are created to form holes which connect the signals in-between the layers of the PCB.
- Copper Plating holes, also known as PTH ‘vias’, are subjected to electroplating to make conductive paths by plating a thin layer of copper.
- Solder masking is the process of putting a protective layer on the PCB. This material is the green coating that we commonly see in PCBs. The purpose of the solder mask is to protect the copper traces.
- Surface finishes are done on the copper pads which are not covered by solder mask, to prevent pad from oxidation, and also for better solderability.
The key processes of printed circuit board assembly (PCBA) include solder printing, component placement, reflow, inspection and testing.
- Solder printing is a process wherein the solder material is patterned into the PCB based on the programmed location of the active and passive components.
- The boards are then passed through a high-speed, automatic Pick-and-Place machine for the mounting of the electronic components.
- Next, boards undergo a reflow step which is a heat process to melt the solder material, creating a metallurgical bond between the surfaces of the components and conductive pads. For through-hole components, wave soldering is applied which is composed of a wave of molten solder coming in contact to the pads of the PCB.
- To ensure the quality of the assembled boards, inspection and testing are required steps prior to packing and shipment.
PCB and PCBA have different testing methods to check for any material, manufacturing, and assembly defects. Bare PCB can be tested two ways—either through Fixture Test or Flying Probe Test. The fixture test involves bed-of-nails fixtures that are aligned to make connection with the target test nodes of the PCB. Simultaneous testing of the test pads is possible with the fixture test, thus making it a more efficient test method. On the contrary, the Flying Probe Test uses probes to access the circuit pads. This is a cheaper but a comparatively slower option. The objective in testing a PCB is to test the continuity of the electrical connections.
PCBA testing can be done through In-Circuit Testing, Flying Probe Testing and Functional Testing. In-Circuit Testing (ICT) is a type of testing used to check manufacturing faults by accessing the components on a PCB through a fixture. This test has a higher advantage for high volume manufacturing. A Flying Probe Test uses probes that “fly” or that can flexibly move around to access certain test points. This test method is commonly used for prototype and low-volume production. Set-up times are shorter and tooling costs are lower for Flying Probe Testers as compared to ICT. Functional testing is a type of simulation by means of powering up the device under specific operating conditions and parameters to check the device’s functionality. Responses are measured to detect component faults, functional failures and parametric deviations.
Since PCB and PCBA go through different processes, potential defects encountered are also different. For PCB, common defects include excess/missing copper, missing hole, over/under-etching, opens and shorts. For PCBA, risks of defects like missing components, excessive solder, defective solder joints and misaligned components. These defects could affect the board quality thus highly automatic detection machines are being used to inspect the defects during the PCB manufacturing process.
Cost in PCB assembly is mainly affected by the electronic components and assembly cost. Other minor factors which are usually added as price adders are packaging, logistics, overhead, engineering, and administrative costs. Considering these cost factors, we can outright conclude that PCBA is more expensive than a bare PCB.
Cost of PCB fabrication is relatively lower than PCBA because of less materials and processes involved in the PCB. PCBA cost can vary greatly due to the electronic components on it, especially the main chips which may be several times more expensive than PCB bare boards. So, the cost of PCBA and PCB are quite different.
PCBA production includes PCB fabrication and PCB assembly, so it is obvious that PCBA has a long production time. Normally, we can produce printed circuit boards in 1-3 weeks, but PCBs with especially material or special technology may take an extra 1-3 weeks to produce. While for PCB, we can source the electronic components in 1-4 weeks lead time normally. But we need to pay attention to the fact that some components may need a very long lead time, such as months. If so, we had to book these components in advance. So, we know that the production time of PCB and PCBA are different.
Now we have a deeper understanding of what is PCB and PCBA and the similarities and differences between PCB and PCBAs. We emphasized on the key items that make these two concepts distinct from each other.
|PCB bare board
|PCB bare board, electronics components
|With electrical connection, no electronic functions
|With full electronic functions
|PCB fabrication, SMT assembly, PTH assembly
|PCB production equipment
|PCB production equipment, pick and place machine, reflow oven, wave soldering machine
|E-testing, In-circuit test, functional test
|PCB Open or short circuit, visual defects
|PCB Open or short circuit, visual defects, missing components, excessive solder, defective solder joints, misaligned components
It is important that you can communicate with your suppliers in a common language to avoid any issues brought about by misinterpretation and lack of understanding. Knowing the differences between PCB and PCBA will also help you to avoid any misunderstanding during the communication with your customers or suppliers, and plan PCB bare board production and electronics sourcing accordingly during the initial phase of your PCB project, especially with regards to cost, materials and production time.