How can the yield rate of mobile phone frame structures be improved to over 99.9% by optimizing the dispensing solution?
In the field of smartphone manufacturing, every detail is related to the final quality of the product and user experience. Among them, the sealing and stability of the mobile phone frame are one of the key factors, and the dispensing process in its production process is particularly important. Today, we will delve into an industry hot topic - how to achieve a leap-forward improvement in the yield rate of mobile phone frame structures through refined and intelligent dispensing solution optimization, aiming for a high standard of more than 99.9%.
Core
Objective: Achieving a “Zero-Defect” Dispensing Process
A
99.9% yield rate signifies a “zero-tolerance” approach to defects. Our strategy
focuses on two key areas: “preventing defects from occurring” and “timely
detection and removal of defects.”
1.
Root Cause Analysis: Identifying Existing Defects
Before
optimization, it is essential to conduct a precise analysis of all defect types
and their root causes under the current yield rate. Common dispensing defects
include:
a.Insufficient adhesive volume: Leading to seal/bond failure
and waterproofing failure.
b.Excessive adhesive volume (adhesive
overflow): Contaminating
internal components, cameras, speaker grilles, buttons, etc., affecting
functionality and appearance.
c.Adhesive breakage: Gaps in the seal line
directly causing leaks.
d. Bubbles: Air bubbles in the adhesive forming
holes after curing, affecting seal strength and consistency.
e. Stringing: Fine adhesive threads form
when the dispensing head is lifted, which may fall off and cause short
circuits.
f. Poor curing: Insufficient strength or stickiness
after curing.
Methods:
Use SPC (Statistical Process Control) tools to analyze production data, perform
teardown analysis on defective products, and observe defect morphology using
equipment such as microscopes and optical profilometers.
2.
Optimization Solution: Comprehensive Upgrades Across Six Dimensions
a. Method - Process and Method
Optimization
This
is the core component.
● High-Precision Dispensing Valve and Pressure Control:
Abandoning
traditional timed jet valves, piezoelectric jet valves or screw valves are
adopted.
Piezoelectric
Dispensing Valve: Suitable for low-viscosity
glues, with high frequency (hundreds of Hz), precise dispensing volume control
in nanoliters, virtually eliminating stringing, making them ideal for the delicate
paths of mobile phone frames.
Piezoelectric Dispensing Valve
Screw valves: Suitable for high-viscosity,
filler-containing glues. Extruded through a rotating screw, they offer precise
control and high repeatability (up to ±0.5%).
Real-Time
Pressure Control: A closed-loop pressure
controller monitors and adjusts the glue barrel pressure in real time,
compensating for pressure loss caused by glue volume reduction and viscosity
changes, ensuring highly consistent glue delivery.
●
Path and Parameter Optimization:
3D non-contact dispensing: Given the
curved and varying heights of mobile phone frames, a laser rangefinder is used
to track the Z-axis height in real time to ensure a constant distance between
the dispensing head and the workpiece, avoiding inconsistent glue line width
due to height variations. Intelligent Path Planning: Compensate for speed and
glue output at the path's starting point, end point, and corners. For example,
speed can be reduced or glue output frequency increased at corners to prevent
uneven glue delivery due to centrifugal force.
Multi-Segment
Parameter Setting: Divide a single glue path
into multiple segments, allowing you to set different dispensing parameters for
different areas, such as straight lines, corners, and interfaces.
Glue
Management:
Constant Temperature Storage and
Transportation: Glue viscosity is extremely sensitive to temperature.
Temperature-controlled glue storage bins, delivery hoses, and dispensing valves
must be used to maintain a stable glue temperature within a ±0.5°C range.
Vacuum Degassing: Centrifuge or vacuum
degassing is performed before the glue is loaded into the pressure drum to
eliminate bubbles at the source.
Automatic Glue Mixing and Purge: For
two-component glue, use a static mixer and set an initial purge program to
ensure a uniform and stable mix before dispensing on the product.
3. Machines -
Equipment and Automation
High-Precision Motion Platform: Utilizes
a high-rigidity, high-precision linear motor or servo motor platform with
repeatable positioning accuracy better than ±5µm to ensure path repeatability.
Machine Vision Integration:
● Pre-positioning: Before
dispensing, a vision system is used to precisely locate the phone frame,
compensating for positioning tolerances in incoming materials or fixtures to
ensure the dispensing path is consistently correct.
● In-Process Monitoring: An
integrated online visual inspection system uses a high-speed camera to inspect
the glue path for continuity, width, and position defects during or immediately
after dispensing. Immediately detect defects and mark the product.
● Post-Process Inspection:
Before curing, a 3D line laser scanner performs a 100% inspection of the glue
profile, measuring the height, width, and cross-sectional area of the glue line
to ensure it remains within strict tolerances. This is a critical line of
defense for achieving a 99.9% yield rate.
● Equipment Maintenance:
Establish a strict preventive maintenance plan and regularly replace consumable
parts such as needles, seals, and mixing tubes. 3. Materials - Material
Consistency Control
Supplier Management: Establish strict
quality agreements with adhesive suppliers, requiring them to provide
inspection reports for key parameters such as viscosity, specific gravity, and
curing properties for each batch of material.
Incoming Material Inspection: The laboratory
conducts random inspections on each batch of incoming material to verify key
parameters and ensure batch-to-batch consistency.
4. Environment -
Environmental Control
Cleanroom: The dispensing area should be
located in a dust-free room to prevent dust from settling on the adhesive path
or in the adhesive.
Temperature and Humidity Control:
Maintain the workshop temperature and humidity within a stable range (e.g.,
23°C ± 2°C, 50% ± 10% RH) to minimize environmental impacts on adhesive
performance and equipment stability.
5. Measurement -
Measurement and Data Feedback
SPC Statistical Process Control: All
inspection data (glue width, glue height, and visual inspection results) is
uploaded to the MES system in real time. Control charts are used to monitor
process stability. If a trend (e.g., a gradual decrease in glue width) is
detected, the system will immediately issue an alert, prompting engineers to
make adjustments before scrap is generated, enabling predictive maintenance.
Full-Process Traceability: Each product is uniquely coded, and all dispensing
parameters, equipment status, and test results are recorded. Any issues can be
quickly traced back to the specific batch, workstation, and even time.
6. People - Personnel
Training and Standardization
Standardized Operations: Develop highly
detailed standardized operating instructions covering equipment operation,
material change procedures, inspection checklists, and exception handling.
Professional Training: Operators and
engineers must not only know how to perform tasks, but also understand why they
are performed and be able to identify early signs of anomalies.
Summary: Key Points
for Achieving a 99.9% Yield Rate
● Shift in Mindset: From
"Post-Inspection" to "Pre-Prevention and In-Process
Control."
●Technological Investment:
Utilizing cutting-edge technologies such as piezoelectric/screw valves,
real-time pressure control, 3D vision positioning, and online/offline 3D
inspection is essential.
● Data-Driven: SPC is the core
brain for achieving ultra-high yields and process stability, making the
production process transparent and predictable.
● Systematic Management:
Optimizing and standardizing every aspect of the process: people, machines,
materials, methods, environment, and testing.
Through this comprehensive approach,
raising the yield rate of mobile phone frame dispensing to over 99.9% is a
completely achievable and scientifically sound industrial goal. This requires
upfront investment and meticulous execution, but the resulting quality
improvements and cost savings (reduced rework and scrap) are enormous.
Second Intelligent has played an
important role in theresearch, development, manufacturing, pre-sales and
after-sales services of fluid dispensing robot, potting and coating solutions
which range from various types of automatic fluid dispensing, potting,
two-component potting machines and coating machines with desktop,
free-standing, inline or cobot combined systems, and widely used in global
electrical, electronics, home appliances, automobile, telecom, pharmaceutical,
automotive electronics, semiconductor, aerospace, LED and more.
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