It s Economics and Performance

Transcription

1 E I ect ron ic Controls Design Inc. Water-Alcohol Cleaning It s Economics and Performance Steven D. Glass Director of Marketing & Sales Electronic Controls Design, Inc. Milwaukie, Oregon U.S.A 1990 Int l Conference of CFC & Halon Alternatives November 27-29, 1990 Hyatt Regency Baltimore Inner Harbor Baltimore, MD, USA 287-A S E International Way Milwdukie, OR USA (503) (800) FAX (503)

2 I. *, 1-! AQUEOUS-ALCOHOL CLEANING, IT S ECONOMICS AND PERFORMANCE BY Steven D. Glass, Director of Marketing Electronic Controls Design, Inc. Milwaukie, Oregon U.S.A. I. Introduction In Europe, over the past few years, the combination of water and alcohol as a cleaning methodology has been well established and documented. With the demise of CFC as a cleaning medium, more effective and less costly materials is a definite requirement. Alcohol and water are relatively inexpensive and are abundant, all over the world. When equipment has been designed exclusively for this process, namely through the use of nitrogen inerting, the test results are remarkable as compared to the materials currently being discussed as CFC-alternatives. Operator safety is assured throughout the process, and the cleaning test results are documented on the built-in printer. The evolution of circuit board cleaning has been influenced by many factors, including the degree of cleanliness required, cost, and, of increasing importance, waste treatment and other environmental effects. Existing systems all have their failings in one way or another. Solvent cleaning with chlorofluorocarbons is being eliminated and is also now relatively expensive. Terpene solvents are at least environmentally better, and aqueous washers have performed well in their particular niche. The next important step in the evolution of board cleaning seems certain to be a washing system based on using an alcohol-water mix, not as part of the traditional cleanliness test method, but as the cleaning process itself. Alcohol and water mixes have been used in Europe for some time with excellent success. The need for a system using that method has become increasingly apparent in this country. Electronic Controls Design, Inc., in the development of its Model 7300 MEG-A-RINSE@ SMD, has produced just such a system. In this paper, we be discussing a batch System. Batch systems have superiority over traditional inline systems because of their ability to completely control the process. The System combines an aqueous cleaning cycle, followed by an alcohol-water cleaning cycle. Both closely controlled to ensure a cleanliness level that meets or exceeds MIL-P requirements. 11. Equipment Used ECD Model 7300 MEG-A-RINSE@ SMD and Alpha Metals Omegameter 600 SMD.

3 111. Cleaning and Control Processes The Cleaning System had two basic cleaning methods depending on whether the flux is water soluble or not. When using rosin flux, the System was programmed through a saponifier cycle followed by a water rinse. A final rinse was used with a continuously purified solution of 75% alcohol and 25% water, kept at an elevated temperature. For water soluble fluxes, a simple water rinse plus the alcohol-water cycle was adequate to attain almost complete cleanliness (although a saponifier may also be used if desired). Since this process emulates the traditional Omegameter test method, postwash testing was entirely unnecessary. Thus the System, in our opinion, is well suited for both military or commercial customers and should be welcomed by all environmentally concerned users. After 15 minutes of the alcohol-water cycle the resistivity and temperature was constantly monitored until an endpoint of 2 megohms cm and 115F was exceeded, thus ensuring an equivalent ionic residue level of 10 micrograms per square inch or less. Since the alcohol-water rinse was done at elevated temperatures, this pass-fail method makes any other test process unnecessary; once the boards have passed, they are clean. The accompanying data covering a variety of assemblies, using the Omegameter methodology illustrates the obvious benefits of the alcohol-water rinse cleaning method: All showed cleanliness levels below 2.0 ugh. For comparison, Cleaning the Phase I1 B-36 cupon with CFC's produced boards with an ionic contamination of about micrograms per square inch; saponifier-aqueous cleaning was about the same. Adding the IPA- water rinse brought cleanliness levels down to the 1.5 to 1.8 microgram per square inch region. ALPHA OMEGAMETER SMD-600 CLEANLINESS MEASUREMENTS PART NUMBER SIZE BEFORE ALCOHOL AFTER ALCOHOL (in.) (ug/in2) (ug/in2) X Adec CPU 9.00 X Adec Control 6.50 X M.O.L.E X Ch Mux 10.0 x Model x X PHASE I1 B-36 (l-mil Standoff)

4 1V. Environmental and Economical Factors In the System, the used alcohol was recirculated through a DI column and a filter and sent back to a holding tank for reuse. Alcohol loss, therefore, was only by dragout and evaporation and was minimal. Because of its evaporative characteristics, alcohol reduces board drying time to a small fraction of that required for water. The cost of alcohol was found to be less than 20% of Terpene and only about 2% of CFC's, indicating a substantial potential reduction in material expenses. Alcohol is easily made from natural products and is abundant in every part of the country and the world. Also available was an optional water classifier that treats and returns waste water to the system or diverts it for disposal, thus reducing water costs and easing waste elimination. V. Programmable Control Essential To achieve consistently clean boards, precise control of all the processes was a necessity. The System's control unit monitored and controlled all cycle functions, including prewash times, wash times, number of rinses, dry cycle, chemistry concentration, and the testing cycles. Programming was done by the operator, who entered the lot number and the cycle parameters on the controller's front panel. While operating, the controller indicated the current cycle status on the LED display. During the cycle, the System printed essential cycle parameters as well as the lot number with current date and time. The programmable functions include, prewash time, wash cycle time, chemistry concentration, and minimum number of rinses. The controller's viewing display included alcohol percentage (temperature compensated), cycle time remaining, sump temperature, sump resistivity, and cycle status. Printouts from the built-in printer consisted of time and date, temperatures of the motor, the sump, and the sample chamber, alcohol percentage, cycle times, alarm points, machine number, and batch number. In order to minimize operator monitoring, the operation of the System has been highly automated. Sensors were placed in strategic locations to monitor processes and fluid levels and to control replenishment and refilling. Others monitors sense temperatures and air flow. The alcohol-water ratio was continuously checked by a specific gravity sensor. When the ratio departed from normal, additional alcohol or water was added automatically. The level of the sump was likewise monitored and refilling was automatic.

5 7300 System Diagram Printing Controller Plenum Flow Sensor IPA Valve Close Nitrogen Pressure Sensor D.'+ Column Filter IPA Replenish Tank Alcohol Control Unit (ACU)

6 .. VI. Requirements and Precautions Because the system used alcohol, safety has been a an important design criterion in the development of the System. First, the alcohol was stored in an external, doublewalled enclosure. In case of power loss, the solution flows back into the container. Nitrogen was used to purge the wash chamber, thus reducing the oxygen content and the flammability of the contents. The pressure of the nitrogen supply was constantly monitored to provide additional protection. To keep the air in and around the system free of flammable fumes, air was pulled in from the bottom periphery of the machine, moved up around the wash chamber and exhausted out the top. Air vacuum sensors were placed to monitor the air flow and automatically shut the system down in case the air flow was interrupted. Accurate temperature monitoring was incorporated to make sure that the temperature of the contents of the wash chamber and sump was maintained well below the critical level. The temperature of the main drive motor was also monitored continuously, and the motor automatically shuts down if the maximum temperature is exceeded. As a further precaution, a leak detector was placed to sense any leakage around the pump seals. VII. Other Construction and Process Characteristics The System cleans boards on edge so that cohesional and adhesional forces better remove contaminants from small spaces and prevents puddling of the cleaning agent. Stacked vertically the boards also drain better with less dragout and more even cleaning with no side-to-6ide differences. The System uses dual, counter-rotating wash arms driven by a high-capacity pump to flood every assembly at a flow rate of 60 gallons per minute (only gallons are actually used per cycle). The arms rotate at a minimum speed of 24 rpm -- a rate calculated as optimal for fast, thorough cleaning. The axial pump is driven by a 113 hp heavy-duty motor to deliver the maximum amount of water with a minimum of expended energy. Loading was easy in the spacious, logically-structured stainless-steel interiors, which accept boards of nearly any size. The baskets are of strong, heavy-gauge wire coated with Plastisor, a durable, rubberized material that resists cracking, chipping, or peeling. Other features include a view window that allows visibility of the interior. V111. Summary ECD believes that the future for consistently achieving thoroughly clean circuit boards lies in the combination of alcohol-water cleaning. In a well-designed system like the

7 System SMD, it is an effective, verifiable, and safe method for arriving at cleanliness levels that will satisfy any military and commercial user, using either rosin or water-soluble fluxes. Alcohol-water cleaning will do so at a lower cost than any other method and without the traditional problems with waste disposal and other negative effects on the environment.

8 '4. (.I I 8 Ttw csrltroller '.,SO contains 2. real-timr clock so that all documentation is automatically timed and dated. Basic Construction and Cleaning Features ECD's batch cleaning systems combine the best in materials and engineering for superior results. I. ECD washers clean boards on edge so that cohesional, adhestional, and gravitational forces remove contaminants from small spaces and prevents puddling of cleaning agent.there is also better draining with less dragout and more even cleaning with no side-to-side differences. 2. ECD washers use dual, counter-rotating wash arms driven by a high-capacity pump to flood every assembly at a flow rate of 60 gallons per minute (only 2Y2 gallons are actually recirculated per cycle). The arms rotate at a minimum speed of 24 rpm - a rate calculated as optimal for fast, thorough cleaning. The axial pump is driven by a Xi hp heavy-duty motor to deliver the maximum amount of water with a minimum of expended energy. 3. Loading has been made easier in our spacious, logically-structured stainless-steel interiors, which accept boards of nearly any size. The baskets are of strong, heavy-gauge wire coated with Plastisor, a durable, rubberized material that resists cracking, chipping, or peeling. Other features include loop-design removable rack dividers. 4 To enrilro qcialitv 2nd rpliabilitv. everv ECD washer undergoes a complete inspection. Ana berore shipping, each washer is run through a 100% test of every cycle to ensure that performance matches design specifications. The Model 7300 with the Alcohol Control Unit. Model 7300 Sample Printouts Batch #0257 Batch Number, 0 1 /O 1 /90 00: 07 : 32 Lot006 - Date, Time, and... Lot Number 7300 MEG-A-RINSE SM) Software Version * Version * Machine N d e r... 12\Machine PRCGRAM LISTINGS Number MAXlMul N PSI Nitrogen MINIM N PSI - Limits WATER CLEANING PRE-WASH WASH RINSE CHEMI STRY MAX PRINSES MIN #RINSES MAX WASH TEMP WASH TEW MI N WASH TEMP illn FINAL RES CLASSIFY WASTE YES 01 min 05 min 01 min 01 % 10 ea 03 EA 139 F 120 F 100 F.SO0 M W R02 AL03H3L CLEANING YES NITROGEN PURGE 01 min ALCCMX WASH 15 min WXALCCWOCCONC 85 % MlN ALCOHOC 03NC 63 % t-ctor TEPP i29 F MAX CLEAN T W 140 F CLEAN T W 115 F MlN CLEAN TEMP 090 F MIN FINAL RES 2.00 M DRY PRINT PEDE 10 min ON... Programmed Washing and Water Rinsing Parameters Programmed Alcohol Washing Parameters Batch # /01/90 01:30:17 Lot MEG-A-RINSE SMD Version * Machine Nurber 12 *... CLEANING CYCLE WATER ALOL YES YES WATER WASH PRE-WASH 01 01:30:23-EVent Final Res.335 M Timing Surp Terrp 105 F >WASH 05 01:32:46 Chemistry 01 4; Resistiviry Final res.002 M- After Water Scmp Terrp 121 F Washing >RINSE :39:07 Final Res.030 scmp T m 137 :\ >RINSE :41:43 \Resistivities Final Res.223 M m A f t e r Water Slnp Tenp 129 F >RINSE :41:43 /-Rinses Final Res.612 M' Sum Te~p 131 F ALccH3L WASH NITRCGEN PURGE 01:47:18 Nitrogen 66.8 PS: ALQ=HOC WAY( 01:48:48 Alcohol CCKlc 75 % Final Resistivity F iria 1 Res 5.30 X- after Alcohol 105 F Washing Sum T w Motor Tarr, 104 F DRAINING 04 02:C4:2: DRY 10 02:08:36 Passed TEST RESULT Final Test +***PASSED*WC* CYCLE CCI"PLL7E 02: 18:36...