This article explains and discusses the guiding principles governing 0201 placement in both high-volume and high-mix assembly operations.
Over the past period of time, 0201 placement has been a key topic of discussion throughout the industry. Due to size, weight and power consumption requirements, many OEM circuit board assemblers need to incorporate even smaller components and technologies into their products. Contract manufacturers (CM, contract manufacturer) must also have new technologies to keep the assembly process up-to-date and provide customers with a complete range of services. For machine builders, the challenge is to develop assembly equipment that is more resistant to obsolescence in an era of dynamic technological change.
0201 placement challenges
The placement of 0201 components is more challenging than the component intervention before it. The main reason is that the 0201 package is approximately one-third the size of the corresponding 0402.
The previously acceptable machine placement accuracy immediately became a limiting factor for the introduction of 0201. In addition, traditional industrial tape packaging (taping) specifications allow too much movement for reliable 0201 placement, and the level of process control must also be improved to make 0201 placement a production reality.
While these hurdles are formidable, they are far from insurmountable. Of course, they require collective determination, since acquiring the technology necessary for 0201 placement requires substantial funding and top management commitment to research and development (R&D).
The Key to Reliable 0201 Placement
SMT equipment manufacturers have produced the ability to make all circuit assembly machines compatible with 0201 at 100% speed, the minimum pickup reliability is 99.90%, the target pickup reliability is 99.95%, and the minimum placement reliability is 99.99%. At the outset, every aspect of the design was evaluated for its capability to a complete 0201 solution, and the combination of single elements with closely related machine element parameters proved critical to achieving success. These parameters include:
Component Feeder Workbench.
The R&D program concluded that the ability to precisely position the carriage table -
And making minimal adjustments to compensate for tape inaccuracies - a key factor in achieving component pickup reliability greater than 99.95%.
In order to achieve this, the feeder table must be precisely machined to ensure repeatable positioning of a single feeder, and a dual-track linear motion guide combined with a high-resolution semi-closed loop servo system is used. The design allows for small adjustments - based on the results of the pick-up accuracy judged by the vision system. This ensures that the component is picked up as close to the center as possible.
Component feeder.
The feeders must be manufactured to extremely tight tolerances to ensure that pick positions remain repeatable despite component height and the large number of possible component position variations. The mechanism used to position and lock the feeder in position must be durable and precise, while remaining user-friendly. In addition, the materials used to make the feeders must be strong and lightweight to allow ergonomic handling while ensuring precise, repeatable feedout of component carrier tape.
Feeder drive sprockets. The drive sprocket plays a key role in the machine's ability to position the component strip. The shape, taper and length of the drive sprocket teeth significantly affect the ability of the feeder to position the strip. Other factors were also investigated, such as the diameter of the drive sprocket and the amount of belt contact with the sprocket. Changes made to the basic sprocket design resulted in improved positioning accuracy, with the earlier design improving by 20% in the X direction and 50% in the Y direction.
Suction head.
After the component is properly fed, the next step is to pick up the component on the vacuum nozzle and bring it to the board. Vacuum nozzles need to be compliant to absorb shocks during component pickup and placement, compensate for small variations in solder paste height, and reduce the risk of component cracking. For these reasons, the nozzle must be able to move within its holder.
Material selection, material hardness, machining tolerances, and thermal characteristics must all be understood in order to construct a reliable tip. The nozzle must move freely within its holder without sacrificing precision.
Nozzle shaft assembly.
The nozzleshaft is also a key design element - by keeping the entire nozzle and shaft assembly directly aligned, overdrive is eliminated. Overpressure is caused by the inertia created when the placement head moves up and down. If the nozzle and shaft are not in line, there is a little whip - or overpressure. Overpressure causes a change in positioning accuracy, which depends on movement speed, nozzle weight and component weight. By eliminating overpressure, direct alignment reduces the number of negative factors associated with component pick-up and placement.
Nozzle design.
The variation in nozzle design is an important factor in allowing the acceptance of 0201 components. In order to pick up 0.6x0.3 mm components, the nozzle must have an outer diameter no larger than 0.40mm. This results in a long, thin nozzle shaft that is fragile to bend but must still maintain precision to maintain high reliability of suction. The change from a straight shaft to a tapered design increases nozzle strength and allows the nozzle to resist bending.
Matrix structure.
All machinery vibrates during operation. Base frame design is a critical first step in reducing the effects of speed and motion that create vibration and harmonic resonance. By using a cast iron base frame and state-of-the-art structural technology, vibrations and harmonic resonances are reduced to manageable levels within the machine so that negative effects can be dealt with.
Up to standard
With all six key factors, the barriers to reliable 0201 placement have been removed. As a result, R&D focus has shifted to newer, smaller components, and 0201 is no longer considered a leading-edge component packaging technology.
For 0201 component placement, the accepted process window is about 0.075mm X and 0.075mm Y at 3 Sigma. In order to achieve 6 Sigma placement reliability, the X and Y tolerances must be reduced to 0.050mm. The latest high-speed placement equipment has a grade of 0.066mm, and the actual standard deviation is about 0.035~0.045mm. Improved accuracy can be achieved as 0201 components become more widely used and manufacturing processes tighten.
Component size differences between suppliers create challenges for both 0201 feeding and placement.
challenges ahead
Although placement of 0201 components is now a standard feature of new placement equipment, additional work is needed to improve the overall process for end users. The relationship between machine builders, component suppliers, board builders, stencil houses and solder paste manufacturers needs to be strengthened to create a more seamless development process. The end result will be a unified understanding of the process, and a better working relationship that will benefit the end user, notably through the incorporation of new production technologies that make it faster and more efficient.
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