Different stages are associated with prototype PCB assembly. Synchronization between these steps is necessary for overall process integration. Compatibility between every stage of assembly and production is crucial with feedback from output to input. This ensures the maintenance of the highest quality levels. It helps in early detection of the issues leading to timely interventions and adjustments.
The different stages in the assembly process are as follows:
- Solder Paste: before adding components to board, the workers add solder paste to board areas that require soldering. These are component pads achieved via solder screen. Solder paste is flux and small solder grains. Its deposition into place is similar to printing processes. Placement of solder screen directly on-board with correct registered position is followed by moving the runner. It moves across screen squeezing solder paste in small amounts through screen holes onto board. Since the generation of solder screen is from PCB files it contains holes on solder pad positions. This way, the deposition of the solder occurs only on the pads. Control of deposit amounts is necessary to ensure right solder amounts on resulting joints.
- The Pick-Place Process: Circuit Card assembly services consider this the second stage of assembly process. This involves board with solder paste addition. Here a component reel loaded machine will pick components from the dispenser. It will then place them at correct board positions. Solder paste tension holds components in place and they will remain so until jolts happen to the board. Sometimes these machines may also add glue for securing components to board. However, presence of glue makes repair difficult except in cases where its design makes it degraded when soldered. Component and position information for programming pick-place machine comes from PCB design information. This considerably simplifies the programming.
- Soldering: after addition of components to board, the next step is the soldering process. Use of wave machines have decreased these days especially in case of surface mounted components. In wave soldering, addition of solder paste to board is not present. Reflow soldering is more popularly in use these days.
- Thorough inspection: after undergoing the soldering position, boards go through inspection. In surface mounted boards with 100+ components, instead of manual inspection, optical automatic inspection is more common. Modern day machines are capable of detecting poor joints, misplaced or wrong components and inspecting the boards.
- Testing: before leaving the factory, electronic components need to undergo tests. These can be of different types and depend upon a wide variety of factors.
- Feedback: proper monitoring of the outputs is extremely important to make sure that manufacturing processes run satisfactorily. This involves investigation of failures detected. Ideal place for this is during the stage of optical inspection. It comes immediately after soldering in a general scenario. This allows quick detection of process defects followed by immediate rectification. This prevents multiple number of boards from having the same issues.
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Source : articlesbase.com
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