Once ALT measures the position of the bonding channel, the hot melt adhesive is jet dispensed on to the channel at a specified distance from the case edge. Control over bead size (diameter and height) and line placement are critical. At Right, the bead profile is measured and a profile given. In this case, the width is measured at 0.311 mm and height 0.165 mm providing the desired size and aspect ratio.
Hot melt is a phase change material that is packaged in solid form and when heated becomes a liquid. The material is sensitive to changes in temperature and humidity requiring the jet to have excellent thermal stability, independently controlled heat zones and high frequency actuation for fast continuous path line dispensing.
Bead Size and Placement
AUTOMATIC LINE TRACKING (ALT)
Shinwa developed Automatic Line Tracking to overcome the challenges with SmartPhone Case to Display bonding operations. The plastic cases used in SmartPhones have channels molded in to them to hold adhesive and bond the phone case and display into a single assembly. Tolerances associated with the plastic injection molding process result in the bond channels being in a slightly different position on each case. In addition, the bond channels on the sides of the case are being made smaller in order to maximize the viewing area of the display. These two challenges make the adhesive dispensing operation increasingly precise.
By detecting the uniqueness of each case prior to Jet dispensing the hot melt adhesive, Shinwa is improving this assembly process for manufacturers. ALT also measures line dimensions after dispensing and provides feedback on system performance. This feedback is used to automatically adjust parameters improving quality and yield. ALT can also measure Solder Paste and other adhesives.
ALT Vision and Sensing Detection Tools
The dispensing system uses a combination of Vision and Sensing techniques to detect the dispensing channel position and then measures the channel size and coordinate locations. The system compares the actual case dimensions to the theoretical case dimensions and modifies the dispense pattern to match the actual dispensing channel locations for that particular case.
ALT detects case to case variances and compensates for these manufacturing tolerances. The dispensing system places hot melt adhesive in the optimal location on the case channel. The part measurement and compensation increases yield and results in less scrap and re-work. saving manufacturing costs while increasing efficiency and output.
ALT Edge Detection and Measurement
ALT identifies the edge of the channel relative to the edge of the case. The picture at right shows small differences in location of the channel edge relative to case edge. Location variance from 10 microns to 50 microns is typical and is common in the case molding and assembly operations.
The dispense pattern and position of the adhesive is adjusted to follow the unique channel location of the part being processed. This correction prevents adhesive from wetting into the active area of the display or wetting beyond the case edge. Shinwa's ALT process control tools and micro dispensing capability minimizes bonding areas and allows more viewing area on the display.
ALT: Dispense Path Optimization
Once ALT determines channel location and surface, the coordinate locations for the optimum dispense path are identified and used to place the dispense pattern in the correct position on the case. The depiction (Right), shows the dispense channel, overflow reservoir and case edge. The hot melt adhesive is dispensed on the bonding surface depicted by the grey color.
Automatic Line Tracking also measures the dispense line dimensions after the cycle is completed. This measurement takes just a few seconds and provides process control feedback to maintain performance within the specified control limits.
Shinwa is solving the challenges of Case to Display Bonding in SmartPhone assembly operations with more intelligent systems that enable new designs and product improvements.
ALT Detecting and Adjusting
The diagram below shows ALT compensation by illustrating Theoretical dispense position, Programmed position (assuming a perfect part), Actual position detected by ALT and adjusted position of the dispensing pattern.