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