Feeder: Key Checks Before Release

A placement machine can only place what its feeders deliver, and a feeder that misfeeds, that lifts a component out of its pocket at the wrong angle, or that runs out at the wrong moment stops the line. Most of the delay in a surface mount line is traced to the feeders rather than to the machine, and most of the resulting defects are traced to the tape rather than to the process.

This article explains the tape and reel standard, how the feeder types differ, how the setup is verified, and what the common failures look like.

The Tape And Reel Standard

Components are supplied in a carrier tape with pockets that hold one part each, sealed by a cover tape that the feeder peels back as the tape advances. The tape width, the pocket pitch, the pocket size, and the position of the part in the pocket are defined by the packaging standard so that any compliant feeder can use any compliant tape. The cover tape peel force is specified as well, because a tape that releases too easily spills parts and one that is too tight lifts the component out of the pocket before the nozzle arrives.

The orientation of the part in the pocket is the property that most often causes a defect. The part sits in a defined relationship to the sprocket holes, and a reel that is wound in the opposite direction reverses that relationship, which places every part rotated by one hundred and eighty degrees. The placement program is written for one convention, so a reel of the wrong orientation produces a board that is fully populated and electrically wrong.

The reel itself is a production variable. A seven inch reel of a small part may hold a few thousand pieces, while the same component on a thirteen inch reel holds several times that, and the number of reel changes during a shift is set by that difference. A large reel reduces the number of interruptions but increases the weight on the feeder and the space it occupies on the cart, and a reel that is too heavy for the feeder causes intermittent advancement as the tape tension changes. The leader and trailer lengths are also specified, because a feeder needs enough tape to thread itself before the first component and enough room to finish without pulling the last part back into the machine.

Feeder Types

Tape feeders are the standard for small components. The pitch of the feeder has to match the pitch of the tape, since a four millimetre tape in an eight millimetre feeder will double feed or fail to advance, and the width of the guide has to match the tape width for the same reason. Stick or tube feeders are used for parts that are not supplied on tape, and tray feeders for large packages that are shipped in a matrix tray, which requires a different pickup routine and often a different nozzle.

Bulk feeders, which take loose components from a reservoir and present them in a track, are used for high volume small parts but require a component that can be oriented reliably from a random supply. The mechanical condition of the feeder matters as much as its type: a worn sprocket, a stretched spring, or a damaged guide produces an intermittent misfeed that is difficult to diagnose because it appears only on some reels.

Setup And Verification

The setup begins with the feeder cart, where each position is loaded with the reel that the program expects. The pickup position is taught for each feeder, the cover tape path and the peel tension are set, and the sprocket engagement is checked by advancing the tape by hand or by a test cycle. The pickup height and the nozzle are matched to the component, and the vacuum is confirmed for a part that is picked by suction.

Verification is a first article that confirms not only the position but also the identity and the orientation of each part. A component that is placed correctly but in the wrong rotation will pass a positional check, so the verification has to include the polarity of the polarized parts and the pin one orientation of the integrated circuits. A barcode on the reel, read at the loading station and compared with the program, is the most reliable way to prevent a wrong part, and a vision check of the first placement catches an orientation error before the whole panel is built.

Handling Practice

Reels are stored in a dry cabinet where the components are moisture sensitive, because the tape and the pockets do not protect against humidity. They are handled as static sensitive material, and the packaging is left sealed until the reel is needed. A reel that has been stored in a humid room and then reflowed without a bake is a popcorning risk that no amount of care on the line can remove.

Splicing is the other practice that repays attention. When a reel runs low, a new one is spliced onto the end of the old tape, and the splice has to preserve the pocket spacing and the cover tape continuity. A splice that skips a pocket, or that leaves a doubled cover tape, produces a pickup error or a dropped component, and a splice performed with the wrong tape may jam the feeder. Machines that monitor the remaining tape and warn before the end are cheaper than the downtime they prevent.

Common Failures

The failures cluster into a few causes. A component that is picked but not placed usually indicates a nozzle problem, a vacuum leak, or a part that is stuck in the pocket. A component that is placed at an angle usually indicates a pocket that is too large or a cover tape that released too early. A pickup error that appears on every cycle of one feeder is a pitch or a height problem, while one that appears occasionally is usually a damaged tape or a worn sprocket.

The wrong part is the most serious failure because it is not visible as a defect. The controls are the barcode verification at loading, the comparison of the reel label with the bill of materials, and the traceability of the reel to the assembly, so that a suspect unit can be identified if the error is discovered later. The way the placement order and the pad positions affect the machine is described under placement order and pad positioning, the layout constraints under layout decisions that affect production, and the footprints under manufacturable design guidelines.

FAQ

Why does the tape orientation matter? Because the part sits in a fixed relationship to the sprocket holes, and a reel wound the other way presents every component rotated by one hundred and eighty degrees, which the placement program does not correct.

What causes a double feed? Usually a mismatch between the tape pitch and the feeder pitch, or a worn sprocket that does not advance the tape by exactly one pocket.

Can a reel be spliced without stopping the line? Yes, with a splice that preserves the pocket spacing and the cover tape continuity. A poor splice shows up as a pickup error at the joint rather than as a defect in the product.