Component placement is taking center stage more so today than ever before. Why? The reason is increasing numbers of different package types and sizes are now used due to shrinking PCBs. The pick and place operation during PCB assembly is demanding greater attention as a result.
This means placement demands a well-disciplined list of checks, being ever watchful of mixing in damaged components, and verifying pad sizes with respective components.
Placement must undergo various checks to assure components are the correct ones and whether or not they’re showing problems.
The first check is at the SMTstage, as shown in Fig. 1. It’s called a feeder component check. QC performs this check so that each part is identified on the tape and reel or trays and is matched with what is called out in the Bill of Materials (BOM). QC then checks item number, component size and values, and assures that what’s called out in the BOM is what’s on the specific tape and reel or the tray.
Considerably more is important to know about the effects damaged components and pad/component verification can have on accurate placement. Check out our Circuits Assembly Magazine article to get more details.
Meanwhile, here are some tips and hints that’ll get you better acquainted with accurate component placement.
- Be careful about “consigned components” because they cause pick and place problems. These parts are cut from the tape and reel and provided to production as an exact number of components. Components must be in a tape and reel package so that pick and place can perform accurate placement.
- Manual placement of “consigned components” creates misalignment, bridging or opens.
- Assure first article inspection is performed prior to reflow to assure all components are the right ones per the BOM.
- Avoid salvaged or “pulled” components that can pose reliability issues.
- Ensure pad designs match with component sizes specified in the BOM.
- Assure that your PCB designers and assembly engineers coordinate and place onto the PCB a global fiducial or GF used for alignment at screen printing and pick and place.
The best of all worlds for you is to have an EMS provider with in-house design and assembly and close ties to a highly reputable fab house. You are assured that assembly and design teams frequently interact to iron out an assortment of placement concerns. Therefore, to have successful and accurate placement, PCB designers must closely interact with assembly and process engineers to assure the right type components are used and placed on the PCBs. They should also define and coordinate the various requirements assembly has.