The following are the required elements for auto assembly:
Gerbers in 274-X (embedded apertures) including fabrication drawing.
Part centroid text file with Reference Designators, external placement layer, and X & Y location and rotation in ASCII format.
Numerical control (NC) drill files
Solder paste file (one of the Gerber files) for all sides mounted
Glue dot file
If possible, the design database, specifying the database format (program name)
Parts list or BOM (bill of material)
Parts or hardware required
The Gerber files are used to define the pad locations and help the assembly house determine where pin 1 is located and provides a heads-up of how the board looks. The database can also be used to determine the location of pin 1. Some board houses choose to make their own solder paste file/stencil. The designer may create the solder paste file to his/her own preference with experience. It is good to learn how and why the assembly house makes its stencils and duplicate it to ensure consistency from each assembly house (the common name for any company that assembles boards). The solder paste file is used to mask the entire board except those areas that will be soldered. Solder paste is applied to the exposed pads and the stencil is removed. Components are applied and held to the board by the solder paste and the glue dots securing the components as they are soldered to the board.
For component placement a part placement/centroid file is required to know where the center of the part is. The layer ID shows what side the part is placed on, and the rotation displays the orientation of the component.
Consistency in rotation of the original component is critical to report. Unless the designer’s software can account for inconsistencies, all components should be created in the same orientation.
NC drill files are used to locate mounting holes and provide the holes sizes for thru-hole components. This also allows the assembly house to determine adequate clearance for the component lead.
A bill of material or parts list is used to reference the designators of the centroid file and the components that need to be mounted. The BOM should also provide information if the component is an SM component or a thru-hole component.
Other considerations for auto assembly are the board size, the panel size, and breakaways. The boards are commonly assembled in a panel that may contain many boards. The panel is the original material that the boards were etched routed in. The panels pass to the assembly house with all boards intact.
Breakaways are the connections around a board that hold the board during assembly but can be broken easily when it is time to remove the board.
1.Ordering a Board
The DFM check looks at all the design specifications of a PCB. Specifically, this check looks for any missing, redundant or potentially problematic features. Any of these issues may severely and negatively influence the functionality of the final project. For example, one common PCB design flaw is leaving too little spacing between PCB components. This can result in shorts and other malfunctions.
By identifying potential problems before manufacturing begins, DFM checks can cut manufacturing costs and eliminate unforeseen expenses. This is because these checks cut down on the number of scrapped boards. As part of our commitment to quality at a low cost
3.Incoming Quality Control(IQC)
PCBBUY Verifying all incoming materials and handling quality problems before subsequent SMT assembly begins. Our IQC position will check following issues of incoming materials if they comply with our strict requirements.
4.Machine programming – Gerber / CAD to Centroid / Placement / XY file
Having received the PCB panels and components the next step is to setup the various machines used with the manufacturing process. Machines such as the placement machine and AOI (Automated Optical Inspection) will require a program to be created which is best generated from CAD data but quite often this isn’t available. Gerber data is almost always available as this is the data required for the bare PCB to be manufactured.
5.Solder Paste Printing
The first machine to setup in the manufacturing process is the solder paste printer which is designed to apply solder paste using a stencil and squeegees to the appropriate pads on the PCB.
Once the printed PCB has been confirmed to have the correct amount of solder paste applied it moves into the next part of the manufacturing process which is component placement. Each component is picked from its packaging using either a vacuum or gripper nozzle, checked by the vision system and placed in the programed location at high speed.
There is a large variety of machines available for this process and it depends greatly on the business to what type of machine is fingers and clothing to the surface of the board. Once all is said and done, the results can look a little dingy, which is both an aesthetic and a practical issue.