Got pick & place? Cool.
Got cut strips components but no strip feeders? No? Then this post is for you.
Problem: You need to assemble a small run of boards in your pick and place and buying full reels of parts makes no sense, instead you get a low count in cut strips. Strip feeders cost a lot, and they are not very special, just cold dumb metal. Of course, the manufacturer will sell you high quality feeders machined from aluminum/steel, but placing components from cut strips that already have pockets spaced evenly sounds like a very easy problem right? I mean you could just stick them on a cardboard with double sided tape and then teach the machine the first+last and it figures out the rest. That works but it’s a pain when you need to reload – you have to re-teach the machine since you won’t stick it exactly in the same place, you’re almost better off placing by hand.
Solution: So let’s make a strip feeder. I have lots of components that are less than a full reel (exotic resistors, transistors, crystals, caps, mosfets etc). Most of these are 8mm and 12mm tape, rarely 16mm. So it would be perfect to have a strip feeder that can be placed in a fixed position in the machine. To reload you just cut the pre-determined length, feed it through and align the first pocket to a marker on the side, reset component count for that row, and machine already knows where to continue, quick and easy.
Dimension and lane width choices. Most larger chips can be sourced in jedec trays and that’s a standard size. So let’s make this strip feeder the same size as a jedec tray (136x320mm), it’s then very easy to place it in the existing tray holder. For this tray I will just make 10x8mm lanes and 2x12mm lanes, you can play around with the design. They should fit exactly as long as we keep lane delimiters at 2.5mm. Here’s what I mean:
Materials. Cut from 1/8″ thick acrylic. I used black for the bottom and mid layers and transparent for the top. You might think why not use 1/16″ since a lot of 8mm taped components are very thin anyway. The reason is that there are lots of components that will require more than 1/16″ height, plus if you need to, you can stack those thin strips ontop of an empty paper strip to raise it a little, so it’s easy to raise a strip in a 1/8″ spacing, but impossible to shrink a thicker tape to a 1/16″ height.
You will also need Weld-ON-3 acrylic cement to glue together the 3 layers. This makes a strong molecular bond (melts acrylic together). It takes only 10-15 seconds for each bond to solidify, and a few minutes to be strong. A small plastic bottle with a thin needle applicator is needed for the cement, only very minute amounts are necessary to melt and bond acrylic. Suck some cement from the big container, and when ready to bond apply a little pressure to the applicator and drag the needle along edges when the liquid comes out, capillary action will pull it in between the surfaces.
Take the DXF file or print to your laser cutter directly from the Corel file (find them here). The next step is to use real component strips to align the thin 2.5mm acrylic strips. Start from one edge, align the acrylic strip perfectly to the edge of the bottom layer, use some small clamps, then use your fingers to hold it for 10-15 seconds. Apply cement 1-3 inches at a time, making sure the delimiters are held straight, since they will not be perfectly straight from the laser heat. Allow a minute or two for the strip to get bonded once it’s all cemented. I then started with the 10 lanes of 8mm tape. Use 8mm tape to space the second acrylic delimiter, clamp the ends, then cement it from the center out. Continue for the rest of the 8mm feeder lanes. The last 2 lanes are 12mm, so use 12mm tape to align the last 2 delimiters. The last delimiter should be right next to the bottom edge, so you should have a nicely delimited set of lanes without any leftover space.
After the mid delimiters layer is bonded you can bond the top layer, this will be a bit trickier since the covers are wider than the mid layer delimiters. Align the top with the botom, they should match corners since they are the same size. Bond the four corners then the outer edges. Then it’s up to you if you want to bond the top layer strips to the mid layer strips or not. They might already be aligned, but sometimes thin plastic tape might want to creep in between them so bonding them is a good idea. Bending the applicator needle can help with getting underneath and into the edge to release the cement liquid. For each lane of the top layer that I bonded, I first inserted tape to make sure the windows do not cover the component pockets, I used some SOT23 tape since these are larger than resistors.
And you’re done. Leave it a few hours for permanent bonding, then it’s ready for action. You might need to raise this in the jedec tray holder, so you may want to add another acrylic strip on the outer edges underneath the bottom layer. Or otherwise adjust the Z axis when picking from the tray to compensate for the lower location of the parts so the head travels far enough for a good pick.