MEMS | ARTICLE
<< Figure 11b: Optimised sealant line. >>
<< Figure 11a: Disconnected sealant line (yellow box). >>
Potential issues If sealant volume control is inconsistent and more sealant is applied in one line, then excessive material can contaminate wire bonding pads or other components near the sealant material after capping. This is a typical failure and re-work can be difficult. When sealant is disconnected due to material void or line width is inconsistent due to un-optimised parameters, this will be a critical failure when it requires certain hermeticity or low vacuum after capping (figure 11).
Motion systems — throughput requirements This section evaluates the impact on throughput by changing motion parameters such as maximum velocity. In addition, two different applicators were used for the experiments. The sealing line width requirement is driven by the geometric constraint of a package structure. Thus a certain needle/nozzle inner diameter, fluid pressure, line speed and others were selected for this study.
Experiment setup: Two different motion parameters were set up. Motion 1 used normal mode and motion 2 applied high-performance parameters. Motion 1 with a single applicator was used as a baseline. Table 1 shows the setup. ‘Dual’ in this case means moving two applicators simultaneously that dispense different MEMS sealing lines in parallel.
<< Table 1 >> Motion Type
Scenario 1 Scenario 2 Scenario 3 Scenario 4
Motion 1 Motion 2 Motion 1 Motion 2
Applicator
Single Single Dual Dual
HEIGHT SENSING AND VISION: It was assumed that the wafer had good alignment and flatness. Thus, three points of height sensing (HS) per substrate and two fiducials (alignment marks) were applied.
DISPENSING DIMENSIONS: A 5 mm x 5 mm square sealing line was used per unit. One panel included 100 units. Each unit spacing was 5 mm pitch.
NON-CONTACT JETTING CASE: Putting down sealant in the desired location can be a challenge when there are tight tolerance and dimension requirements. It is important that the dispensing system provides constant velocity during dispense in order to put down the droplet at consistent distance intervals. Cycle time per unit is shown in figure 12. Total time of handling and dispensing includes handling, vision, height sensing and dispensing time.
<< Figure 12: Cycle time. >> Cycle time per unit =
Total time of handling and dispensing Number of units per tray
Applicator velocity during dispensing was determined by flow rate and other requirements such as line width. In this case it required a 0.3 mm line width and thus a small orifice nozzle was needed to make the small volume droplet. Work-time dispensing means the duration of the applicator putting down sealant material. Applicator velocity was locked to 42 mm/s during dispensing patterns of square sealing units as work-time dispensing. Motion-time dispensing is defined by non-dispense move time between square sealing units. Non-dispense moves of 5 mm were used in this experiment as each unit pitch and two different motion parameters showed significant difference in cycle time by reducing motion-time dispensing. Figure 13 shows that high throughput can be achieved by high-performance motion parameters or normal motion parameters with dual applicators. A large portion of motion-time dispensing (51%) is allocated in Motion 1 and thus a dispensing system with high-performance
44 | commercial micro manufacturing international Vol 6 No.5
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