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SMT Trends & Technologies: A Pocket Full of Components
September 19, 2012 |Estimated reading time: 5 minutes
Editor's Note: This column originally appeared in the August 2012 issue of SMT Magazine.There you are, standing with a bag of loose components and pieces of tape after being asked to produce the batch. You won’t get any additional components and there are barely enough available to produce the batch in the first place. You only have the exact quantity of the larger and more expensive components at your disposal. You have little room for pick-up errors so you need to deliver with the highest quality.
With a decrease in batch sizes, a large amount of assembly time is wasted by an increased number of setup changes. Time-consuming elements include loading and/or unloading feeders, changing feeders and nozzles, adapting board support, tuning and teaching new components, and ramping up. And, unless supplied with board data, program and data preparation can also take some time.
Another characteristic of smaller batch sizes is a limited number of accompanying components. They come packed in all forms: In a bag or box, Styrofoam packing, small stick, partial carrier tape, and many others.
We should be asking whether any form of feeding could standardize the process. It is better to not use too much manual handling to avoid damaging components before they enter the pick-and-place equipment. What are the alternatives for feeding just a handful of components?
Most Components Supplied on Tape
We’ll start with the most commonly used packing form: Tape. More than 80% of a board is populated by components coming from tape. Most will be resistors and capacitors, but there will usually be just a few (much larger) controllers on a board. When components are supplied in just the right amounts, the wider the tape becomes and fewer components from the tape are placed. All this translates to the pieces of tape becoming shorter (sometimes very short).
To reduce the chance of not picking a component, the first pick must be good. All other picks are then a fixed distance (pitch) from each other.
A tape consists of a carrier and a cover tape. If the tape is cut off just in front of the first and just after the last component, there is not much to hold onto. The cover tape must be peeled off reliably and the carrier tape must be transported. Two ways to go are:
- Extend the cover tape. The pick position should be located after the index mechanism. (The carrier tape must be gripped to actually position the first component, although this also means there could be no grip for the index mechanism with the last component or components.) If components are re-used at a later time, they remain covered by the original cover tape. This is common for 8mm type components.
- Remove the cover tape completely. In this case the tape is positioned as a static one-by-many matrix within the pick reach of the machine. The total strip length must then be shorter than the available pick area. If the tape is not static and an uncovered tape is instead indexed, then the machine’s construction should ensure that components remain in their cavities. Then, however, the pieces of tape are uncovered and less suitable for re-use. Feeding uncovered tape can be accomplished using a tape lane format (with indexing) or a tray format.
Other Components Supplied on Stick
The second-most commonly used packing format is the stick. Components are packed in stick to protect them, so they should stay in the casing. Depending on the number of components supplied, the sticks provided can come in a large variety of lengths. Ahead of time, you will not know what components you will actually get. So, having all the correct component-dedicated stick feeders beforehand is simply not possible.
The most practical method is to cut out the front of the tube (to the size of the component) and use this as the pick-up location. This avoids transitions, always critical, from stick to the pick-up location in the stick feeder.
The most common problem with the generic tracks is the optimum vibration each component actually needs to transport the component. Mixing too many different component types on one generic top plate can lead to components jumping out of their lanes, or larger components being transported too slowly. Smaller, generic top plates will, on average, feed more without errors than a very wide type. So, with only a few supplied components, smaller generic plates are preferred, but still not perfect. Controlling the stop/movement per stick is best, but more costly.
How to Deal with Loose Components
And that pocket full of components. What to do with these? Since there are literally thousands of possible shapes it is not easy to come up with a standard form of feeding. You don’t want to have to re-pick every component, though, or handle them manually the entire time. For now, they end up in customized (stick) lanes, or on a customized tray, but all must be hand placed into these packings first.
It would be nice to see a packing emerge to deal with the decreasing number of components with smaller batches. In the meantime, you need to ensure that the pick-and-place quality remains high. When the first component’s pick location is taught, the remaining picks can be guaranteed using a fixed pitch/index. Once a successful first pick is guaranteed and the remainder of the component locations are fixed, then pick-and-place is practically a given, and components only need to be supplied in the right quantities. Eric Klaver was born in Rosemere, Quebec, and, via Oklahoma, he moved with his family to Holland at the age of 12. After finishing school, he became a radio officer for the merchant navy. After studying computer science where he learned how to program and design ICs Klaver enjoyed a career at Philips. This was followed by a move to Assembléon in 1998. As commercial product manager he translates high-level technical developments into easy-to-understand commercial material. Klaver specializes in vision technology and feeding and is currently the chairman of IEC work group TC40WG36, which specializes in component packaging.