One of the hottest topics in SMT assembly today is placement of the latest ultra-small component package: the 01005. The 01005 (or metric 0402) measures just 0,01” x 0,005”, half the width and half the length of the previous smallest component, the 0201. As of this writing, 01005s are still rare, but that has not stopped most SMT equipment vendors from touting their ability to place them.
The placement of 01005s presents challenges in nearly every aspect of the assembly process. Special solder pastes must be used, stencil aperture and thickness must be carefully controlled, placement machines must be able to pick and place the components reliably, and even the reflow profile may need to be adjusted to accommodate these tiny parts.
Other equipment such as AOI/AXI and especially rework are also affected. But the never-ending push of miniaturisation dictates that the 01005 is here to stay and likely will become commonplace in the near future. This article focuses on the placement-related issues of 01005s.
High-volume production demands high-reliability picking and placing. At 25% of the total surface area of an 0201, the 01005 is especially challenging to pick up, centre and place accurately and reliably.
Frame design: To pick 01005s, the most basic requirement is a machine that has an accurate and repeatable positioning system. The use of rotary encoders is typically very accurate when a machine is new, but mechanical wear can reduce their accuracy over time. Linear encoders, on the other hand, measure true head position and offer higher and more consistent accuracy.
Another key component of positioning repeatability and accuracy is the system’s basic construction. For the highest reliability, best accuracy and longest life, the machine’s frame should be as stiff as possible. A one-piece cast frame is recommended because this design incorporates the base frame and both Y axes into a single casting, resulting in an extremely rigid platform.
With the high speed of today’s machines, this rigidity is key to being able to place components accurately over time. Compared to welded and bolted steel frames, a cast frame will provide much better stiffness over a longer period of time.
Feeder design: The feeder is also a critical component, as it has been since the widespread adoption of the 0402 many years ago. At that time, it was discovered that typical 8 mm feeders did not have sufficient accuracy for reliable picking. This process started again with the 0201 a few years ago, and again for the 01005.
It would be easy to claim one’s machine can pick and place 01005s using existing 0201 feeders, but when there is only 25% of the surface area to work with, this is not a practical claim. A system designed specifically to pick and place 01005s is necessary.
01005s are currently quite expensive, making it critical to have minimal part loss. The price for a 0402 resistor is typically about $0,003 to 0,004 each. It jumps tenfold for 0201 resistors to $0,03 to 0,04 each. For 01005 resistors, the price is ten times the price of 0201s, or about $0,45 each.
If history is any guide, these prices will come down dramatically as production volumes increase, but for now, 01005s will probably only be considered in space-premium applications.
So would you be willing to accept a pick ratio of 99,8% for a component that costs $0,45 a piece (and basically impossible to find after they are lost)? Probably not. At that rate, if just ten 01005s were placed per board on a run of 1000 boards, you would be throwing away $90 per run.
For this reason, a special 01005 feeder that can meet the high pick reliability customers require for such expensive parts is mandatory.
Centring. The last part of the high-reliability picking equation is the nozzle. Here we can see one of the benefits of laser centring. Camera-based centring systems take an upward-looking view of the component. With a component as small as the 01005, it is likely that the component is even smaller than the nozzle, which can create centring difficulties if the camera confuses the nozzle for the component.
Laser centring measures the component from the side. So if the nozzle tip is bigger than the component, it creates no problems for centring. A special nozzle that has a rectangular tip instead of the typical round tip provides key advantages. This design holds the 01005 better, reduces the chances of a tombstone pick and increases the pick reliability.
Once the component is picked, the challenge is to centre it accurately. Again, laser centring is ideal for this situation. Using a laser with approximately 5000 pixels is key to accuracy.
Typical camera systems are just 1000 x 1000 pixels. This means that when measuring an 01005, the effective size of the component is 30 x 15 pixels using laser centring vs. about 9 x 5 for a camera system (more is better).
Excitement over the 01005 continues to grow and forecasts show increased use in the future. It is safe to assume that 01005s will find their way into many more products as the price comes down and they become more widely available.
It is important to recognise the challenges this will present to the entire SMT assembly process. Juki addresses this challenge with four key elements:
* A one-piece cast frame for rigidity and long-term accuracy and repeatability.
* Specially designed nozzles for high reliability.
* Specially designed feeders for accurate component presentation.
* Laser centring that can more accurately measure and handle ultra-small components.