Who can most benefit from SMT Caddy?
Any business or individual, requiring frequent surface-mount, electronic board fabrication:
• Small businesses, requiring custom electronic board assemblies
• Any establishment, developing custom electronics which often requires multiple concept revisions for evaluation and testing
• PCB assembly job-shops, producing prototype and short-run assembled SMT boards for clients
• Entrepreneurs and hobbyists with frequent need for custom electronics
SMT Caddy can pay for itself within the first few custom PCB assembly projects (perhaps, less than 10 prototype boards!). Furthermore, the convenience of turning around prototype and evaluation boards very rapidly is invaluable in any engineering or R&D environment.
I have never stencil printed PCBs before; any suggestions?
Just about all PCB fabrication houses, domestic and abroad, offer stencil fabrication services as well (etched or laser cut, both work well). The stencil data would be available in your Gerber files, produced by any standard software you may be using. So, you can have a stencil made for your specific board for a very reasonable price.
There are many choices for manual stencil printers in the market. They are reasonably priced (<$100-$500, depending on size and features). This would be the obvious solution. You should follow the guidelines of your printer manufacturer to decide the features for your stencils.
For a DIY and no-cost solution, and for prototyping and small batches, stencil printing is actually quite simple. All you need is a simple, flat stencil; don't bother framing or folding edges for low volume (less expensive).
To print your boards, you'll need the board fixtured on a flat surface. For fabricating multiple boards, it'd be best to have a way of placing the boards repeatably on your fixture. This can be achieved by machining a pocket or placing pins in a plate (if you have that capability) or, by glueing a few thin locators on your surface (your locators should be thinner than your PCB so the stencil can lay flat over the fixtured PCB.). Thin strips of sheet metal, plastic, etc., all work well.
Now you're ready to setup your stencil. Ideally, you'd want to raise a platform from your fixture plate, the same thickness as your PCB. This could be a piece of the same PCB material (panel edge remnants, etc.), or anything else you may have that's about the right thickness. Glue this down on an edge as well. The stencil can be now taped to this raised platform (one edge only to serve as a hinge; use a nice tape like polyester, kapton, etc., so it doesn't lose it's integrity as you fold it back and forth. Ideally, you'd like it to stand up to alcohol as you'll use that a lot to clean up your paste! You need to lay the stencil on your located PCB and align it as best as possible before affixing your tape hinge.
To print your paste, make sure the stencil and PCB are very clean (alcohol wipe works great). You'll need a squeegee; ideally, this is a hard polyurethane plate, but, a razor blade works for smaller boards, or, a thin piece of plastic or sheet metal, with a very flat and smooth edge for larger boards. Dispense paste in a bead line across the width of the board, on the stencil. A 45° squeegee angle works well to pull the paste over the stencil. Don't repeat if you missed some pads! More than likely, you'll smear the printed pads. Clean and start over until you get the hang of it.
There are many articles and tutorials on the net as well, for more details and other approaches.
What if I want to dispense (rather than print) solder paste for a coarse and quick prototype?
Dispensing solder is, of course, always an option though tedious! Any standard (time and pressure type) solder dispensing unit can be used to produce a rough prototype for proof of concept. Naturally, small components, leadless chips, or larger boards would not be reasonable for manual solder dispensing, but, certain simple boards may justify this approach for prototyping. SMT Caddy's integrated digital microscope is a nice aid for manual solder dispensing.
How accurately should I place the components on bumped pads?
One nice thing about bumped pad solder reflow is its relative forgiveness regarding placement accuracy. During reflow, the melting solder naturally collects to the center of the pad due to liquid surface tension. Equally, the component leads tend to center over the molten solder to balance the forces produced by surface tension. The end result is an auto-correction mechanism for reasonable placement errors! Of course, you can't have the component placed off the pads, or bridging pads!
What is the best oven to use for solder reflow?
Industrial solder reflow ovens are available from many manufacturers (batch, conveyorized, multi-zone, inert atmosphere, etc.).
For the do-It-yourself-er bunch though, simple and inexpensive units are available for well under $500 and use IR (infrared) lamps. Quite frankly, we prefer a convection toaster oven! They are even less expensive and produce better results due to more uniform temperature gradient by recirculating the hot air. You can go an extra mile by adding µcontroller based kits for profiling the temperature vs. time (available kits in the market). A basic oven works quite well as long as it can go at least 10°C beyond your paste's reflow temperature. You'd like to pick a unit with high enough power to have the ramp-up capability (achieving the temperature fast enough). A point worth noting: standard convection toaster oven choices diminish at higher temperatures, often required for lead-free pastes. Alternatively, Eutectic pastes offer relatively low melting temperature which facilitates far easier and quicker reflow process and relaxes the requirements on the reflow system.
Of course, you'd NEVER use this unit for preparing food, after it has been exposed to solder fumes!
Can I change SMT Caddy's lefty/righty configuration myself?
Although handedness reconfiguration is possible to perform after manufacture, it is a lot more convenient to order SMT Caddy in the preferred configuration.
We can provide the reconfiguration for a fee after purchase. Please contact us for further details.
Should I lubricate the linear ways' shafts?
NO!! Unlike conventional linear ways, there are no 'linear bearings' in our design, hence, no need for lubrication. We utilize Shielded ball bearings which are internally lubricated. In fact, best results are achieved by having clean, dry shafts. Particles can produce bumpy motion, or, hesitation.
How many feeder modules should I buy?
It really depends on your project sizes and board variations. We recommend a minimum of 15 feeder modules (20 to be safe) for the hobbyist/entrepreneur. This allows populating the banks with a few wider feeder module configurations, and, most of them configured for 8mm tape (passives are most often supplied in 8mm tape format, and, are by far the highest feeder quantities one sets up!). SMT Caddy can accommodate 20 feeder modules, simultaneously, if they are all configured for their minimum width of 8mm. In the case of a professional job shop, for example, it would be very convenient to have MANY feeder modules preloaded with the most popular components and values so that job setups are much quicker by pulling the preloaded modules from inventory.
The system can be purchased as a starter package, which comes with 10 feeders (you can add more from our store if you like), or, in case of buying more than one system and sharing feeders, you can buy the SMT Caddy without feeders.
Do I need to buy any special Styli for general PCB assembly?
Not unless you use ultra-small chip packages! The standard system is shipped with 6 styli, which will manage components as small as 0402 (inch). The largest stylus is capable of managing ICs as large as 15-20 mm without a rubber cup, and larger by attaching the rubber tip of choice (also included). There are a couple of special purpose styli (telescopic design with spring-loaded tip) which should be purchased, only if you're planning to use 0201 or smaller chips.
How do I figure the maximum length of tape I can wind on the standard feeder module reel?
It is a good idea to figure the correct length of tape to cut before winding it onto a feeder reel. The maximum tape length the reel can accommodate is:
6 / (maximum tape thickness (mm)) in meters
0.75 / (maximum tape thickness (inch)) in feet
For example, if you have a 1.5mm thick tape, you can wind 4 meters of tape on a reel (6 / 1.5), or, if you have a 1/16" thick tape, you can wind 12 feet (0.75 / 0.0625). Of course, most often, the maximum length isn't necessary and a short strip is all that is needed, unless, a larger production batch is being set up.
Why don't the feeder modules allow standard 7" reels to be loaded directly?
We forfeited this convenience for the benefit of miniaturization, cost reduction, and maximizing feeder density. Standard 7" reels are wider, heavier and of course, larger in diameter. This would have required SMT Caddy to grow much in size for the same number of modular feeders. Furthermore, the micro-miniature feeder motors, indexing via the cover tape, would have to be replaced by larger motors and sprockets directly indexing the carrier tape, approaching industrial tape feeder style mechanisms, dramatically increasing the feeder module size and cost. And, quite frankly, full-size reels are usually not purchased for prototyping or small run jobs!
I have some difficulty deciding location versus height of components as I approach the placement point. Any suggestions?
Video microscopes are 2D devices. As such, there is no depth perception associated with 2D viewing (as compared to a stereo, optical microscope, which facilitates 3D viewing). This is where the integrated laser pointer fits in. You should adjust the laser dot position before starting a job, if necessary. The laser dot should be adjusted with a planned offset from the tip of the stylus, as the stylus is lowered and touching the surface of your PCB. Once adjusted, the laser dot shows the landing position of the tip of the stylus (keeping in mind the offset), independent of the spindle/stylus height in motion. The suggested offset is to allow for the beam to travel past the component on the stylus. You'll make any fine adjustments necessary as you approach the board, via microscope imaging.
Laser dot position adjustments are necessary as board thicknesses change, or if your stylus has been bent in any way. Of course, a bent stylus also produces a wobble as you rotate components which cannot be accommodated by laser adjustment! Try to straighten any bent styli before you start a job, or, get replacements (listed in our spare components section) if they are severely damaged.
Approaching the place height via naked eye, before resorting to the microscope image for fine placement, is quite comfortable and efficient. All this will become second nature after a little practice!
What is a reasonable component placement rate with SMT Caddy?
An average operator, once having developed a comfort level with the system, should be able to place 250-500 components per hour. Of course, component styles (leadless vs. leaded, pin pitch, etc.), as well as component sizes play a big role in the throughput.