Custom PCB Assembly
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All PCB projects begin with part procurement. Once the details of a project are finalized, parts are sourced and a BOM (Bill of Materials) is sent out containing all necessary details regarding the components, manufacturers, and shipping details. After the BOM is approved by the customer, all parts are ordered and your project can officially begin once they arrive. As parts arrive, they are sorted according to project, then scanned and added to our internal system so that they can be tracked throughout the PCB assembly process. This ensures that all components are placed correctly and any issues can be traced to their source.
Before components can be added to a board, solder paste must be applied to the appropriate areas, usually component pads. Solder paste consists of a metal alloy powder suspended in a putty-like substance called flux. Applying precise amounts of paste is essential as too much or too little solder can result in misaligned or unconnected components. This is achieved using either a solder screen, or a jet printer. A solder screen is produced during board design and has holes that align with where solder is needed on the board. Paste is applied to the screen and a runner is scraped across forcing the paste through the holes in the screen and applying it to the appropriate positions on the board. A jet printer receives coordinates for where paste must be applied on the board. Similar to a typical printer, paste is deposited onto component pads as tiny dots in a grid. Jet printers are incredibly precise and significantly reduce the amount of wasted solder paste per project, however they are not as fast as a screen print.
Next, pasted boards - called wet boards - receive their components. Some larger components and through-hole components are placed by hand after, but a majority of components make their way onto the board via pick and place machines. As suggested by the name, pick and place machines pick up a component and then place it in the correct location on the board. Components are loaded into the pick and place as reels then, using the provided software, the location and position of all parts are defined. When the run begins, one or many heads will grab the parts, orient them according to the design specifications, and place them onto the wet solder which will hold them in place until they can be permanently fixed through soldering.
Once a board is populated, the solder must be melted in order to adhere all of the parts to the board. Depending on size, placement, and type, components may be secured using a variety of methods including hand soldering, reflow ovens, and selective soldering. Reflow ovens use conveyor belts to carry boards through a series of heating and cooling zones. Technicians adjust the conveyor speed and zone temperatures to achieve custom time and temperature profiles that will melt the solder used in each project. Selective solder machines use a set of coordinates to direct a nozzle that creates a small molten fountain across un-soldered components. Parts that need to be selectively soldered are usually surrounded by parts that have been previously soldered in a reflow oven and the selective-solder process must be sufficiently precise to avoid damaging them. When selective soldering is not viable for a PCB assembly, our trained technicians solder by hand using the latest Metcal soldering equipment.
Inspections occur periodically throughout PCB production (such as wet board solder paste inspection powered by AOI) but a majority of inspections take place once a board is finished. Manual inspection is not an option for surface mount boards employing hundreds (or more) components but, with the assistance of 3D AOI and X-Ray, boards are able to be thoroughly screened. AOI utilizes high intensity flashes of light to illuminate imperfections on inspection items and read part numbers. Once programmed, it can detect every components’ presence, location, and orientation in a matter of seconds. Using volumetric height information, 3D AOI also detects bent, lifted, and bridging leads and can verify part coplanarity. X-Ray is a non-invasive and non-damaging form of inspection and is necessary for detecting internal defects or viewing parts occluded by other components. 2D X-Ray is ideal for individual board or component inspection and is especially useful for void analysis. 3D inspection uses thousands of snapshots to reconstruct whole or partial boards and components for in depth inspection of even the tiniest parts.
Finally, after obtaining all necessary parts, soldering them to the boards, and passing all proper inspections, the finished boards are almost ready to be shipped. Boards undergo some light cleaning to remove any extra paste, glue, or other residue obtained during the build process; then they are carefully packaged using industry standard, antistatic materials and sent out to the customer.