The printed circuit board (PCB) assembly process consists of various steps that must be performed in the proper sequence for the finished product to function as designed. When you assemble a printed circuit board, you must choose the right technology for the type of components at hand.
There are a number of individual stages with a PCB assembly or manufacturing process. All of the parts and pieces must be correctly aligned in their designated spot, as specified in the PCB design. Any deviation, ever so slight, can have huge ramifications on the functions of the finished board.
Solder Paste Stenciling
Stencil, which is manufactured from metal or polymer, is applied with solder paste to all of the pads on the bare-board. This process is typically referred as solder paste stenciling. Stencil is used for solder paste stenciling process that consists of a bunch of holes and resembles to the SMD footprint pads on bare-board layout. The stencil is placed over the boards and a layer of solder paste is squeegeed over it. This leaves a nice and uniform layer of solder on the SMD pads. The primary function of solder paste stenciling includes binding, connecting and cleaning.
Pick and Place
Development of pick and place systems or robots is directly related to the growing importance of surface mount technology. These systems have become an important aspect of PCB assembly line. Pick and place systems offer automated, faster and highly efficient solutions during the assembly process. They place components automatically on the PCBs.
The growing preference towards automated pick and place systems over manual placement is credited to the relatively faster operational rate and minimum errors.
Reflow soldering has gained significant attention over the past few years, particularly for its use in attaching surface mount components to printed circuit boards. Reflow soldering is primarily used to form the required solder joints. This process is carried out by pre-heating the components and solder paste, and melting the solder without causing damage.
De-ionized water cleaning of assembled boards
Deionized water is used for the cleaning of PCBs before they leave the shop floor. It is a very glacial form of water, which lacks ions. Whenever a board is made or revamped, there is a substance called flux, that is residue on the board. Over a period of months, this flux buildup winds up clingy, looks bad and can turn out to be marginally acidic prompting a debilitating of solder joints which will cause corrosion and longevity issues.
To clean the boards after assembly, we place the batches into “dishwashers”. Dishwashers are nothing but high-temperature, high-pressure, all stainless-steel device. Because de-ionized water has such an affinity for ions, the inside of the dishwashers is made completely of stainless steel. Any other metal would quickly disintegrate.
The dishwashers use de-ionized water to remove any residue from the fabrication process. The dishwashers utilize a closed-loop system. After they are done washing the batches, the used water gets accumulated and is tested for conductivity. If the electrical conductivity is very low, it is inferred that the wash phase is complete. Then, the waste water is recycled through very high-quality filters.
Inspection and Quality Control
It is critical to ensure the quality and reliability of PCBs for consistent performance of various electronic equipment. However, rising complexity associated with miniaturization of electronic devices and complicated structures is driving the need for advanced inspection and quality control techniques.
We give major importance to inspection and quality control at every stage in PCB assembly. Further, inspection and quality control are performed by our industry experts in several different stages including visual inspection, structural inspection and automatic inspection. These technologies improve performance and offer overall defect coverage. Optical inspection, laser triangle measurement, X-ray inspection and X-ray lamination technology are some of the major technologies used in automatic inspection. Each of these technologies offers distinct benefits over another.
Through-Hole Component Insertion
A through-hole component is commonly identified as a device that is soldered with a wire or a metallic lead and mounted to the board. These components are placed with the help of the lead on plated holes of the board. Soldering is performed after placing these components on the respective plated holes. Important factors to be considered include quality of the solder joint and the connection.
Strong mechanical bonds make through-hole component insertion technique superior to the SMT technique. Other advantages include reduced available routing area for signal traces on layers and cost-efficiency. Limited routing space for signal traces on layers are available for all lower layer on multilayer boards as holes pass through all layers on the opposite side.
Mechanical Customized Insertion
The need for customization of mechanical components has risen over the past few years. Different types of mechanical components include wires, heat-sinks, spacers and stand-offs, screws, and connectors. The effective adoption of customized insertion solutions involving various mechanical components will ensure performance enhancement for PCBs.
In addition, edge mount connectors and linear connectors also require customized insertion during PCB assembly. The use of turret solder for press mount terminal, which requires specialized tooling like swage tools, is also part of mechanical components.
Conformal coating is typically used for protecting circuit boards from harsh environmental conditions, including moisture and chemical contaminants. The conformal coating is applied on PCBs and acts as a protective chemical coating or polymer film with a 25-75µm thickness. Conformal coating also helps to maintain long-term surface insulation resistance (SIR), thereby ensuring the operationality of the assembly.
Final Inspection and Functional Test
FCT, also known as functional testing, is carried out during the last phase of the PCB assembly line. This is typically required for a final quality control test in order to ensure performance of the circuit board is as per given requirement.
The final inspection is performed by trained and sharp-eyed professionals who check for any defects such as scratches and mechanical errors on PCBs. After the final inspection, an inspection report and documents are generated for customers, thus signifying proper working of PCB. The PCBs are vacuum-sealed, bubble-wrapped, and securely boxed for shipping.
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