AUTOMATED CO2 COMPOSITE SPRAY CLEANING SYSTEM FOR HDD REWORK PARTS

Transcription

1 AUTOMATED CO2 COMPOSITE SPRAY CLEANING SYSTEM FOR HDD REWORK PARTS D.P. Jackson Cool Clean Technologies, Inc. PurCO2 Cleaning Products Division IDEMA ASIA PACIFIC 2007 CONFERENCE Introduction CO 2 spray cleaning has been commercialized over the past 20 years for a variety of applications The advantages of CO 2 spray cleaning are: Can be very gentle (cleaning of wire bonded dies) Can be very aggressive (paint removal for aircraft) Overcomes boundary layer limitations of typical liquid cleaning Is a dry non-polluting cleaning method No drying after cleaning is required Virtually no cleaning debris disposal to address The potential issues with conventional CO 2 snow spray cleaning are: Condensation of particles from the surrounding environment Condensation of moisture on the surface being cleaned Loss of cleaning energy with increasing nozzle to part distance 1

2 CO 2 Spray Cleaning Principles Very high energy levels needed to remove sub-micron particles High fluid velocities needed to penetrate the boundary layer Turbulent flow must be sustained to increase shear stress Low hardness of CO 2 snow yields a non-abrasive process Using various nozzles, pressures, temperatures and flow rates: Shear stress can be controlled from 1 MPa to 60 MPa, more than sufficient to cause solid snow to sublimate to liquid at the surface of the part Thin organic surface layers can be effectively removed CO 2 snow cleaning combines physical momentum, phase change phenomenon and solvent energy to remove particulates and thin film contamination Conventional Snow Spray Cleaning Uses a DeLaval type (convergent-divergent) spray nozzle Exhibits a gas/solid unbalancing effect at the nozzle exit Atmospheric drag tends to make the stream diverge rapidly 2

3 CO2 AEROSOL SPRAY Liquid CO2 DeLaval Aerosol Spray Nozzles FINE PARTICLES ENTRAINED IN COLD HIGH VELOCITY CO2 GAS Atmosphere Conventional Cryogenic Spray Cleaning Uses a DeLaval type (convergent-divergent) spray nozzle Exhibits a gas/solid unbalancing effect at the nozzle exit Atmospheric drag tends to make the stream diverge rapidly Results in a two phase aerosol caused by a rapid Joule- Thompson expansion process Wastes liquid CO 2 Causes sublimable solid particles to expand rapidly Results in significant loss of cleaning agent Requires nozzle exit to be very close to surface to be cleaned Cleaning effectiveness can be compromised by the entrainment of atmospheric contaminants into the cryogenic flow stream To prevent moisture condensation on the clean surface, process must be done in a controlled environment with dry N 2 or CDA 3

4 Advanced CO 2 Composite Spray Uses a heated propellant stream around the cryogenic stream Delivers a coherent and concentrated two-phase flow Mechanical action of the solid-gas aerosol spray is highly effective for removing particulate and thin films The heated propellant effectively prevents moisture condensation without requiring a dry controlled environment The propellant stream effectively prevents the condensation of environmental particles by the cryogenic stream Effectively provides more snow to the surface to be cleaned with very little waste in the form of liquid or gaseous CO 2 Can be effectively used with automation due to the ability to clean with a much wider nozzle to part spacing than with a DeLaval nozzle CO2 COMPOSITE SPRAY Efficient Condensation to Coarse or Fine Particles Liquid CO2 Capillary Condenser Coaxial Flow Hot CDA Coanda/Coaxial Composite Spray Nozzles Coanda Flow Atmosphere SIZED PARTICLES ENTRAINED IN HOT HIGH VELOCITY GAS Patented and Patents Pending 4

5 AUTOMATED CO2 CLEANING SYSTEM 70 atm PHASE Forming DIAGRAM a FOR CO2 Composite CO 2 Spray CO (l) 2 2 SUPERCRITICAL REGION 1. Gas Phase 2. Liquid Phase PRESSURE CO (s) 2 3 TRIPLE POINT 5.11 atm, C 1 CRITICAL POINT 73 atm, 31.1 C 3. Solid Phase 4. Composite Spray CO (g) 2 1 atm DRY ICE Propellant Gas (P/T) C TEMPERATURE 30 C AUTOMATED CO2 CLEANING SYSTEM CO2 Composite Spray Cleaning Energy Peak Impact Stress Coaxial v. Coanda kpa (70 psi) 80 Deg. C (358 K) capillary Impact Stress/MPa % Coanda M Coaxial SS 4:4 10% Distance from Nozzle Exit/cm 5

6 Unique Hard Disk Drive (HDD) Cleaning Requirements HDDs which fail functional testing are reworked and retested The rework process requires the removal of screws which results in particle contamination of the components to be reused The Motor-Base Assemblies (MBAs) have fluid dynamic bearings which cannot be cleaned aqueously or with solvent immersion The Covers have filters attached which cannot be cleaned aqueously or with solvent immersion The Voice Coil Magnets (VCMs) can be cleaned aqueously or with solvent, but a dedicated cleaner would be needed to prevent magnetic particle cross-contamination Therefore, a dry cleaning system which can clean the reclaimed parts to prime part cleanliness levels is required Cleaning costs have to be competitive with a liquid system in spite of liquid not being applicable to the rework parts of interest Cleaning Throughput and Cost The HDD industry is very cost competitive and every process that is implemented must be cost effective as well as technically viable For CO 2 cleaning to be adopted as a rework process, high throughput and consistent results were mandatory The most effective way to achieve the rework cleaning goals was by designing a high throughput, automated robotic cleaning system The final design incorporates: Dual robots to clean both sides of the parts simultaneously Four nozzles per robot to clean four rows of parts at one time Pallet loading and unloading while cleaning is taking place Flexibility to clean any HDD form factor via barcode recipe control Class 10 cleaning environment Universal pallet design which can be tailored to almost any part 6

7 CO2 Composite Spray Cleaning Cost Comparison Deionized Water (Immersion/Drying) Composite CO2 Spray (Selective Spray) $0.12-$0.13/part $0.015-$0.06/part $0.06/part (50% - 88% cost reduction - fully burdened/3 year) Best for Complex Surfaces Ionic Cleanliness * Cleans Disassembled Devices Best for Semi-Planar Surfaces Non Non-Ionic Cleanliness * Cleans Partially Assembled Devices * Note: Centrifugal Liquid Carbon Dioxide Cleaning (with Surfactant) may be considered for complex ionic cleaning applications. 7

8 AUTOMATED CO2 CLEANING SYSTEM Automated CO2 Composite Spray Cleaning System AUTOMATED CO2 CLEANING SYSTEM Cleaning Efficiency and System Performance The performance of the system is evaluated using ultrasonic extraction and liquid particle counting (LPC) of the parts Large populations of before and after CO2 cleaning samples have been evaluated Typical reductions of 15 to 25% are being consistently achieved CO2 cleaned parts routinely achieve prime part cleanliness No physical damage to the parts occurs due to the gentleness of CO2 snow cleaning and well thought-out pallet designs Machine reliability for the past six months has been better than 99.9% up time The machine does not require any preventative maintenance due to the selection of lifetime lubricated mechanisms 8

9 CO2 Composite Spray Cleaning Consistency Prime Average WDC MBA Rework Proprietary data removed Conclusions By forming a good supplier/customer relationship, a machine which met all of the customer requirements was developed and built A second generation design has been developed incorporating all of the lessons learned from the first generation machine By having a good understanding of the goals prior to the start of design, false starts and errors were avoided The resulting machine is a very reliable tool which is exceptionally flexible and is expected to be in service for many years The basic machine design can be used to serve many different requirements and is not limited to HDD parts The tool is environmentally friendly and does not generate any byproducts which require handling or disposal 9

10 AUTOMATED CO2 CLEANING SYSTEM For additional information David Jackson Senior Vice President of Marketing and Chief Technology Officer Cool Clean Technologies, Inc. PurCO2 Division Avenue Scott Unit C Valencia, CA A white paper is available for this presentation: Send request to Mr. John Lee, john.lee@coolclean.com 10