Circuit board assembly is a vital step that transforms bare PCBs into functional electronic devices. It requires the synergy of advanced machinery and expert hands to bring your designs to life.
Thru-hole technology involves drilling holes into a PCB through which component leads can be attached. These holes must be the correct size for the component’s leads.
Printed circuit board
The printed circuit board is the foundation of many electronic devices. The specialized copper contacts on the boards help electronic signals pass freely throughout the device. They also provide mechanical support and auxiliary functions.
The PCB fabrication process begins with a schematic capture through an EDA tool, followed by component procurement and placement. During this phase, the designer must be mindful of part positioning while still keeping in mind network connectivity. They must consider the location of heat sinks, physical obstructions, and other factors that could impact performance.
Initially, each component had wire leads that were inserted through holes in the copper PCB traces. This method of construction is called through-hole construction. Moe Abramson and Stanislaus F Danko of the Army Signal Corps developed the auto-assembly system that eventually accelerated production and led to today’s standard Printed Circuit Board (PCB) fabrication methods.
Once technicians have finished imaging and etching, the PCBs undergo optical inspection (AOI). This step is vital to ensure that the boards meet their design specifications. Without it, the boards would have shorts and other defects that can lead to failure in the field.
Components
During PCB assembly, the bare circuit board is “stuffed” with electronic components to form a functional printed circuit assembly. The components may be inserted through holes surrounded by conductive pads on the substrate’s surface or through a circuit board assembly solder paste applied directly to the surface of the PCB. This method of PCB board assembly is known as surface-mount technology.
Prior to assembling a circuit board, it is important to verify the correct parts are available. This includes conducting a design for manufacturability check. This process examines all design specifications and identifies any issues that could negatively impact the functionality of the final product.
After reflow soldering, the finished PCB undergoes a thorough visual inspection and automated testing procedures. The results of these tests circuit board custom ensure proper solder joint formation and component alignment. Any defects identified are addressed using touch-up soldering techniques. Once the PCB is functional, it is packaged for distribution.
Layout
The layout of a printed circuit board is intricately woven into the design and manufacturing process for electronic devices. It determines where essential components like resistors, capacitors, and integrated circuits (ICs) must reside, as well as how they harmoniously interact with each other through an intricate network of conductive pathways.
The first step in PCB layout is the creation of a schematic, a logical representation of the board’s circuitry. Once the schematic is complete, it can be imported into a PCB layout and component placement tool. The next step is routing the traces that connect the components on the board. This involves ensuring that the traces do not cross areas of excessive noise, which could degrade the performance of the final product.
Many older printed circuit boards were assembled using through-hole components, which required their leads to pass through holes on the board. However, modern circuit boards are primarily built with surface mount (SMD) components, which can be placed without having to pass through the holes. This is more efficient and allows the board to be fabricated quickly.
Etching
The etching process is used to create the PCB’s copper layers. These contain conductors called traces and pads for connections, as well as features such as solid conductive areas, vias, and grounding holes. The etching process is essential for creating consistent and uniform traces with straight sidewalls and minimal errors. It also helps to minimize solder shorts between traces and undesired electrical contact with bare copper.
Several different methods are available for etching a PCB, but the most common is an acidic method using Ferric Chloride or Cupric Chloride. This solution is incredibly corrosive and can cause damage to the board if it is left in it for too long. Using the alkaline solution instead is much safer, but it is slower and less precise.
Printed circuit board assembly is a complex process that requires attention to detail. Modern technology streamlines the process to reduce human error and ensures quality. For example, automated pick-and-place machines speed up production and increase accuracy. Moreover, modern reflow systems ensure consistent and reliable connections by controlling temperature profiles during the soldering phase. They also provide lead-free options that align with industry norms and environmental considerations.
Soldering
Soldering is a vital process in creating circuit boards. During this process, electrical components are joined together using a tin-lead alloy. The solder melts, bonds to the workpieces in a surface alloying process called wetting and holds the joints together with tensile strength. When performed properly, soldering is reliable and easy to repair. However, it’s important to follow safety precautions when working with soldering tools and keep the workspace clean. In addition, it’s important to use the right amount of solder and clean the components before soldering them.
During the soldering process, the circuit board is placed on a conveyor belt and passed over flowing tin-lead solder in a pan. Often, to prevent movement, the component parts are held in place with small dabs of adhesive or secured with a fixture. This process is known as wave soldering and is used for thru-hole components, but with the right preparation it can also be used to solder surface mount parts.
Hard soldering, also known as brazing, joins dissimilar metals by melting a liquid filler into the gap and binding them through atomic diffusion and magnetization. This type of soldering is typically done on larger metallic components and requires a higher temperature. Rosin flux is sometimes used to remove oxides from surfaces before soldering. It’s important to keep in mind that rosin flux can cause health issues if it comes into contact with skin or is inhaled.
