Is there anything worse than cut tape? Sadly, yes.

Previously I wrote about how providing your components on cut tape slows the SMT assembly process for the assembler, because they need to mount your tape on a reel before putting the reel on the feeder.

There is one thing worse than cut tape, and that is loose components! You might think it is a saving to just buy a bag of the components you need, but if you are using a professional assembler, it is often cheaper to buy in bulk on a reel, or to make use of the very reasonable reeling service from suppliers like Digikey or Mouser, where your small number of components are mounted on a reel, ready for assembly.

So, what do we do when we receive loose components? Some are taken out of their plastic bags and put into a belt or tube feeder. For others, we need to design and print a special matrix tray, and then manually place the components into the matrix tray. For really short cut tape, we stick the tape into the matrix tray area with removable double-sided tape. For each tray or short cut tape, the pick and place machine needs to be programmed to indicate the dimensions of the tray and the type of component contained in it. As you can imagine all this preprocessing takes quite a bit of time. So, do think twice about how you provide components to your friendly assembler!

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Custom matrix trays set up in the Europlacer pick and place machine. Also a short piece of cut tape with only two components, stuck into the matrix tray area.

 

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Seven years of electronics assembly

Seven years ago today we received our first pick and place machine, a Novastar. Since then we’ve upgraded to a high-speed Europlacer XPii that can handle smaller components. This month we have acquired an Exmore VS-500 vapour phase reflow oven. With the addition of this unit, we can achieve a more even temperature across circuit boards, regardless of the uneven thermal mass of some designs, meaning fewer tombstone errors on assembled boards.

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Our new Vapour Phase Reflow Oven.

Why is Cut Tape such a Bad Idea?

Cut tape wastes an assembler’s time and may cost you more money than you save on parts

When getting your short run of PCB assembly for your design you may be tempted to just buy cut tape for your parts, since full reels have thousands of components on them and may cost more. However, consider what happens when you provide cut tape to your assembler.

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Cut tape mounted in feeder elements 1 and 4. All other feeders contain reels of components.

For each cut tape, the assembler needs to mount it on a feeder, so parts can be automatically fed into the machine for placement.

Peeled back tape
The end of the cut tape has been peeled back to allow a leader tape to be attached using some joiner tape. Components need to be removed from the exposed pockets.

Each feeder needs a couple of feet of blank leader tape, attached with special tape to your piece of cut tape. The first 3 or 4 components worth of cut tape will need to be peeled back to attach the leader tape.  Those 3-4 components need to be repocketed at a later time in the cut tape, which leads to extra manual handling and can be a source of error and lost parts.

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Attaching joiner tape

If you also supply only the exact number of parts required for your boards, the assembler may need to spend extra time dealing with misfeeds, or possibly not do a complete run for you due to dropped components. If you do choose to use cut tape, supply at least 5 additional components, to allow efficient handling.

Let’s look at some costs associated with an example run. Suppose you have 20 pieces of cut tape for your job. For each tape, there is ~$1 of joiner tape needed, plus about 10 minutes of extra time per type of component. At average engineer rates of ~$50 per hour this adds about $200 to your job. If you are only doing 20 boards, that’s $10 per board. Figures will differ for different manufacturers, and some machines may be better or worse at handling cut tape, but as a rough estimate, assume that your job costs $10 more per cut tape and that you will fail to get a complete run unless you supply extra components.

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Leader tape secured with joiner tape

A further thing to be aware of is that there is no guarantee that you will get a single piece of cut tape for each part when you buy your components as cut tape. You may end up with several pieces, and each of these needs to be mounted separately. The extra pieces of cut tape will either stop production as they need to be mounted when the previous pieces have been consumed, or they will take up extra feeder slots. The number of components lost in production is proportional to the number of pieces of cut tape for the part. Since it is known that components provided as cut tape can be in multiple pieces of tape, assemblers will either have to assume the worst when they give you a quote, wait until they see the components before giving a quote, or just give an estimate before the job.

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Pick regions for cut tape and normal tape. Note the length of the leader tape in each case.

 

 

 

 

 

 

 

There are various solutions to the curse of cut tape.

  • Buy a full reel
  • Buy your small number of components and get them put on a reel for manufacture by the supplier (eg. ~$7 reeling fee for a “digireel” from Digikey)
  • For standard components such as passives, you might be able to cheaply use the assembler’s reels. We like to encourage the use of our stock of standard passives, and may even provide these for free for your job, as it saves us time and hassle.

Getting your design ready for manufacture

We sometimes get asked how to prepare a design for manufacture on a pick and place machine. There are things to be aware of that are not needed for your prototype, including fiducials, which are marks on the board that help the machine’s vision system place the components accurately. Also the way that components are provided makes a lot of difference to how long it takes to set up the run.

An excellent introduction to design for manufacture is provided by Dave Jones. We strongly recommend watching it before sending your design to be made. Having said that, we can handle 0402 sized components, but are happy to use other sizes if required.

Welcome to Agile Electronics

Hello world!  Agile Electronics has been providing electronic assembly services since 2010. We’re located in the Melbourne metropolitan area. We have a Europlacer XPii-IIT pick and place machine.  We can provide surface mount assembly services for prototypes to runs of ~1,000 units.

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