0201 assembly, from difficult to conventional placement
This article explains and discusses the guiding principles governing 0201 placement in both high-volume and high-mix assembly operations.
By Ming Gan, ming@smthelp.net
Although generally considered to be a relatively recent development, printed circuit boards (PCBs) have been available since the early 1950s. Since then, the demand for smaller, lighter, and faster electronic products has driven electronic components, PCB, and assembly equipment technology toward SMT.
The earliest general acceptance of SMT occurred in the early 1980s, when machines such as the Dynapert MPS-500 and FUJI CP-2 entered the market. At that time, 1206 (3216) resistors and capacitors were the most popular placement components. However, in one or two years, 1206 gave way to 0805 (2125) as the most common component package for SMT placement.
During this time, both machines and components evolved rapidly. As the machine became faster and more flexible, the 0603 (1608) component began to evolve. At this point, many assembly machine manufacturers went back to the R&D, research and development lab to re-evaluate the technology used to accommodate these newer, smaller components. Higher resolution cameras and smaller vacuum nozzles are among the variations that these components bring to the assembly equipment.
The emergence of 0402 (1608) packaging poses further challenges in all aspects of PCB assembly. In terms of machine development, vacuum nozzles have become smaller and more fragile. A new focus is placed on the component’s feeder, which acts as a unit for improvement, giving the machine more accurate parts.
With the advent of 0402 components, process challenges have increased to those that need to be addressed for successful component placement. Solder paste printing becomes even more critical – stencil thickness and solder paste mesh are increasingly important process considerations. The technology required for such placement also involves significant new costs.
The combination of these factors creates a new form of packaging that is the slowest to adopt in the history of the electronics industry. In total, for almost five years, 0402 packaging was widely accepted in the industry – and many assembly plants today never put a 0402 sheet.
Now, I entered 0201.
Over the past year and a half, 0201 placement has been a key topic of discussion throughout the industry. Due to the size, weight and power consumption requirements, many OEM 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 more resistant to obsolete assembly equipment in an era of dynamic technological change.
0201 placement challenge
The placement of the 0201 component is more challenging than the component intervention in front of it. The main reason is that the 0201 package is approximately one-third of the corresponding 0402 size.
The previously acceptable machine placement accuracy immediately became a limitation of the introduction of 0201. In addition, the traditional industrial tapeding specification allows for too much movement for reliable 0201 placement, and the level of process control must be increased to make the 0201 placement a production reality.
Although these obstacles are very large, they are far from insurmountable. Of course, they need all the determination, because the technology necessary for the 0201 placement requires a lot of money and top management’s promise of research and development (R&D).
The key to reliable 0201 placement
At FUJI, the aggressive R&D program has produced the ability to make all circuit assembly machines compatible with 0201 at 100% speed, with a minimum suction reliability of 99.90%, a target suction reliability of 99.95%, and minimal placement reliability. It is 99.99%. In the beginning, every aspect of the design was evaluated for its ability to work on a complete 0201 program, and the combination of single elements of closely related machine component parameters proved critical to success. These parameters include:
Figure 1 Component feeder table. The R&D program concluded that the ability to precisely position the carriage table – and make minimal adjustments to compensate for the inaccuracy of the tape – is a key factor in achieving component pickup reliability above 99.95%.
To achieve this, the feeder table must be precision machined to ensure repeatable positioning of the individual feeders and combined with a high-resolution semi-closed-cycle servo system using a two-track linear moving guide. This design allows for minor adjustments – based on the results of the suction accuracy as judged by the vision system. This ensures that the component is as close as possible to the center.
Component feeder. The feeder must be manufactured to extremely tight tolerances to ensure repeatability of the suction position, regardless of component height and a large number of possible component positions. The mechanism used to position and lock the feeder in position must be durable and precise, yet be user friendly. In addition, the materials used to make the feeder must be high in strength and light in weight to allow for ergonomic operation while ensuring precise, repeatable delivery of the carrier tape.
The feeder drives the sprocket. The drive sprocket plays a key role in the ability of the machine to position the component tape. The shape, taper and length of the drive sprocket teeth significantly affect the ability of the feeder to position the tape. Other factors have also been investigated, such as the diameter of the drive sprocket and the number of belts in contact with the sprocket. Changes to the basic sprocket design resulted in improved positioning accuracy, with earlier designs increasing by 20% in the X direction and 50% in the Y direction.
Figure 2 sucks the head. After properly feeding the component, the next step is to draw the component onto the vacuum nozzle and bring it to the board. Vacuum nozzles are compliant to absorb shock during pick-and-place components, compensate for small variations in solder paste height, and reduce the risk of component breakage. For these reasons, the nozzle must be able to move within its fixture.
Material selection, material hardness, machining tolerances, and thermal characteristics must all be understood to construct a reliable suction head. The nozzle must move freely within its holder without sacrificing accuracy (Figure 1).
The nozzle shaft is assembled. The nozzle shaft is also a key design element – eliminating overdrive by keeping the entire nozzle in direct alignment with the shaft assembly. Overpressure is caused by the inertia generated when the head is moved up and down. If the nozzle and the shaft are not in a straight line, there is a little whip – or overpressure. Overpressure causes a change in positioning accuracy, which is determined by the speed of movement, the weight of the nozzle, and the weight of the component. By eliminating overpressure, direct alignment reduces the number of negative factors associated with component pick-and-place placement (Figure 2).
Figure 3 nozzle design. Variations in the design of the nozzle are an important factor in allowing the 0201 component to be received. In order to draw a 0.6×0.3 mm component, the nozzle must have an outer diameter of no more than 0.40 mm. This forms a long, thin nozzle shaft that is fragile but must also maintain precision to maintain high reliability of suction. Changes from the linear axis to the tapered design increase the nozzle strength and allow the nozzle to resist bending (Figure 3).
Matrix structure. All machines generate vibrations during operation. The base frame design is a key first step in reducing the speed and motion effects of vibration and harmonic resonance. By using a cast iron base frame and state-of-the-art structural technology, vibration and harmonic resonance can be reduced to a controllable level within the machine, so that negative effects can be dealt with.
Up to standard
Through all six key factors, the obstacles to reliable 0201 placement have been eliminated. As a result, R&D’s 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 approximately 75 μm X and 75 μm Y at 3 。. To achieve 6 贴 placement reliability, the X and Y tolerances must be reduced to 50 μm. The latest high-speed placement equipment has a rating of 66μm with an actual standard deviation of approximately 35~45μm. As the 0201 component becomes more widely used and the manufacturing process becomes tighter, improved accuracy can be achieved.
The difference in component size between suppliers poses a challenge to 0201 feeding and placement. Bulk feeding is being opened and should be available in 2001.
Although the machine now has this capability, only a small percentage of users will be ready to take the 0201 placement in the next 12 to 24 months. This is similar to the introduction of a ball grid array (BGA) and 0402 components, in which the machine’s capabilities are ahead of the process state.
Challenge ahead
While the placement of 0201 components is now a standard feature of new placement equipment, additional work is needed to improve the overall process for the end user. The relationship between machine builders, component suppliers, board manufacturers, formwork factories, 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 end users, especially by making new production technologies faster and more efficient.
By Ming Gan, ming@smthelp.net
