RE: Comments, Stakeholder Review Draft B GMP, OTC Model Rule for Solvent Degreasing 2011

Transcription

1 August 22, 2011 Gene Pettingill State of Delaware Department of Natural Resources and Environmental Control RE: Comments, Stakeholder Review Draft B GMP, OTC Model Rule for Solvent Degreasing 2011 Dear Mr. Pettingill, is a supplier of precision cleaning agents to Electronic Hardware OEMs (Original Equipment Manufacturers), EMS (Electronic Manufacturing Services), and Advanced Packaging (Microprocessors, Integrated Circuits, and Memory Devices) companies as well as a broad array of Industrial Equipment Manufacturers (motor parts, housings, etc.). Kyzen recently learned of the OTC Model Rule and ask that your department consider this late response. Table of Contents 1. Executive Summary 2. Electronic Assemblies 3. Solubility Methodologies 4. Contamination and its Effects on Electronic Assemblies 5. Five Cleaning Forces 6. Comments to the OTC Model Rule 7. Aqueous Cleaning Processes 8. Exhaust Engineering Controls 9. Conclusions 10. References 11. Mike Bixenman Qualifications 1

2 1.0 Executive Summary Cleaning is an important step in assuring reliability of the electronics device for its intended function. The OTC Model Rule for Solvent Degreasing 2011 section on cold cleaners with a recommended limit of permissible VOC to 25 grams/liter is a concern. As devices miniaturize in size, the flux composition in the solder alloy relies on higher molecular weight resins, activators, and functional additives to facilitate a strong metallurgical bond. The cleaning agents needed to remove flux residues from circuit assemblies require a combination of dispersive, polar, and hydrogen bonding forces. A VOC limit of 25 grams/liter is inoperable for a vast majority of the solder material residues used when assembling complex circuitry. Over the past 10 years, there have been significant advances in aqueous cleaning agents and cleaning equipment for cleaning electronic assemblies. Formulations with less than 25 grams / liter VOC have been designed, but data from numerous studies indicate that these cleaning products do not match up well with many of the common flux types used to assemble printed circuit boards. Kyzen has worked with numerous electronic assembly companies in the State of California subject to the 25 grams/liter VOC rule. For high value production, many of these companies have located their assembly operations outside California, with this rule being one of those considerations for leaving California. Electronic manufacturers are faced with the dilemma of determining the level of cleanliness needed to produce reliable hardware. The question of how clean is clean is more challenging as conductors and circuit traces are increasingly narrower. 9 Residues on a printed board, component, or printed board assembly increase the risk of premature failure or improper function, complicate the manufacturing process, and represent a decrease in quality. 2

3 Kyzen has compiled a library of solubility data on many of the soils used to build electronic assemblies. The flux component is an important enabler to creating acceptable solder connections. The soldering materials required to assemble complex circuitry must be stable at temperatures exceeding 240 C. At these elevated temperatures, flux compositions must be thermally stable. Water soluble flux compositions do not possess the thermal stability required to solder many lead-free circuit assemblies. Cleaning products formulated at 25 grams / liter do not remove many of these soils. Low volatile oxygenated solvents formulated into aqueous engineered materials have been successfully combined with water for cleaning most of the residue types present when assembling printed circuit boards. To achieve the desired effect, the cleaning formulation requires a combination of dispersive (solvency), polarity, and hydrogen bonding forces. Supplementing the solvency with inorganic builders, bases, and / or acids creates significant material compatibility, reliability and subpar cleaning concerns. For building electronic hardware, cleaning agents that allow the use of VOC materials up to 200 grams / liter provides formulation flexibility for meeting electronic assembly cleaning needs. 2.0 Electronic Assemblies Electronic devices innovations have changed the way people communicate, interact and work. As the current trends toward miniaturization take hold, proper cleanliness levels become more difficult to achieve. High density circuit designs by definition allow only smaller spacing between conductors yielding a larger electric field, which in conjunction with insufficient cleaning can lead to electrochemical failures. Cleaning is an important step in assuring reliability of the electronics device for its intended function. As devices miniaturize in size, the flux composition in the solder alloy relies on higher molecular weight resins, activators, and functional additives to facilitate a strong metallurgical bond. The cleaning agents needed to remove flux residues from circuit assemblies require a combination of dispersive, polar, and hydrogen bonding forces. This 3

4 response to the OTC seeks to help the commission understand the need for cleaning and limits needed to accomplish the cleaning task. 3.0 Solubility Methodologies The process cleaning rate theorem holds that the rate at which a solvent or cleaning agent dissolves a residue (static rate) plus mechanical energy (dynamic rate) equals the process cleaning rate. 1 To determine the static cleaning rate (rate at which the cleaning agent dissolves the residue in the absence of mechanical energy), Kyzen uses two static cleaning tests. The first test develops a composite solubility parameter for each flux residue in the test matrix. The solubility parameter provides insight into the material sets that dissolve the residue and the chemical characteristics of the residue. The second test exposes each flux residue to different cleaning agents in an effort to match up the right cleaning agent to the soil matrix. This testing provides insight into the technology base options for cleaning the residue set. The test methodology defines a sphere (Figure 1) from the properties of specific solvents and engineered cleaning agents that were exposed to the soil. The test provides a set of solvent/cleaning agent properties that match up (dissolve) the soils in the test matrix. The objective is to develop a sphere whose circumference is defined by the solvents/cleaning agents that dissolve the soil (inside solvents represented by blue circles). Solvents/cleaning agent s inside the sphere are considered relevant solvents, which have properties that require the least amount of mechanical work to dissolve the soil. Red squares represent solvents/cleaning agents that did not dissolve the soil efficiently. These solvents/cleaning agents are considered outside solvents. The properties of the inside and outside solvents/cleaning agents provide insight into the properties of the soil and forces needed within a designed cleaning agent for dissolving the soil. 4

5 Outside Solvents Inside Solvents Figure 1: Solubility Sphere Each solvent tested has a dispersive, polarity, and hydrogen bonding value (Figure 2). These values can be used to determine the optimal properties from which a cleaning agent will rapidly dissolve the soil. The values for each solvent and their distance from the center of the sphere can be used to calculate a composite solubility parameter for the soil. 5

6 Figure 2: Solvent Families Tested 2 Oxygenated solvents in combination with functional additives have been formulated with water and are highly effective at removing rosin, no-clean, and water soluble flux residues. The cleaning agents are effective at concentration ranges of 3-20% in water, depending on the flux residue composition. At these concentration levels, the VOC content ranges from grams per liter. Figure 3 shows a second Teas chart showing the solvents position. Higher dispersive forces are in the right hand corner, higher polarity forces increase in height on the right side of the triangle, and higher hydrogen bonding forces are closer to the base on the left side of the triangle. For effective cleaning, these forces need to align with these same forces in the residue. For example, a no-clean flux residue (most common in industry) contains a combination of materials encased in a resin. To clean this residue, the cleaning agent requires a combination of dispersive forces to dissolve the resin, polarity forces to dissolve polar materials through positive and negative attractions, and hydrogen bonding forces to solubilize the residue in an aqueous medium. By taking away any one of these forces, the cleaning medium will not be optimal. 6

7 Higher Dispersive Forces Figure 3: Solvent Positions within the Solubility Sphere 3 Other factors such as temperature, concentration of aqueous cleaning agents, and time can be designed into the test matrix. These other factors provide information for determining the process window. The test methodology provides two critical insights: 1.) The chemical properties needed to dissolve the soil 2.) The process conditions in the form of time, temperature, and concentration needed to clean the soil in the selected cleaning equipment. A limitation of static testing methodologies is that the method does not take into account dynamic energy and its effects on cleaning the part. Dynamic energy delivers the cleaning agent to the soil and with the right forces improves cleaning performance, even with boundary cleaning agents. Stronger forces applied directly to the source have been found to improve soil removal. In theory, cleaning agents that are a closer match to the soil complement the source of energy and open the process window. 7

8 Solubility testing methodology can be used to develop and correlate the solubility properties of known specific solvent / cleaning agent families to determine the cleaning properties for any soil. This method was used to determine the cleaning properties needed to clean flux residues from the following soldering materials. 1. Lead-Free Water Soluble #1 2. Lead-Free Water Soluble #2 3. Tin-Lead No-Clean #1 4. Tin-Lead No-Clean #2 5. Lead-Free No-Clean #1 6. Lead-Free No=Clean #2 The six solder pastes in this study were reflowed onto test vehicles and exposed to a series of solvents with known solubility parameters. The test coupons were graded based on each solvent s ability to dissolve the residue. The test values were used to calculate a composite solubility parameter for each solder paste tested. Each test solvent has a dispersive value (solvency power for dissolving a soil), polarity value (positive or negative charge attractions), and hydrogen bonding value (sharing electrons with electro-negative atoms such as oxygen, nitrogen, and fluorine). Each of the solder paste flux residues in the test matrix were immersed into the test solvents. The test coupons were graded using values between one and six based on the solvent / cleaning agent s affinity to dissolve the soil. A 1 represents an inside solvent/cleaning agent that matches up well with the soil and a score of 6 has no effect (Figure 4/Table 1). 8

9 Figure 4: Grading Scale 1-6 Score Description 1 Easily cleaned No residue 2 Light residue 3 Moderate residue - Boundary cleaning agent 4 Reluctant to clean 5 Low level cleaning 6 No interaction with cleaning agent Table 1: Grading Description The combined dispersive, polarity, and hydrogen bonding values for each soil tested were used to calculate a composite set of solubility values for each soil (Figure 5). These values provide insight into the chemical properties needed to dissolve the soil matrix. Soils with high dispersive values tend to be more covalent in structure. Soils with high polarity values possess reactive sites with solvents that have a partial positive or negative charge in the valence electron shell, which increases dissolution from the forces of attraction. Soils with high hydrogen bonding values tend to have oxygen or nitrogen within the molecular structure that readily share their electrons with hydrogen, which improves the soils dissolution in water based cleaning agents. 9

10 Dispersive Value Polarity Value Hydrogen Bonding Value Figure 5: Solubility Values Water Soluble Lead Free Solder Paste Flux Residues The solubility parameter for water soluble lead-free solder paste #1 had a moderate dispersive value, low polarity value and high hydrogen bonding value. The solubility parameter for water soluble lead-free solder paste #2 had a moderate dispersive, polarity and hydrogen bonding values. Figure 6 provides a view of the solvent families that were effective at dissolving the flux residues from these two water soluble lead-free solder pastes. 10

11 Interaction Plot for Water Soluble Lead-Free Solder Pastes Data Means 5 4 Soil Water Soluble LF 1 Water Soluble LF 2 Mean Solvent Family 1 Solvent Family 10 Solvent Family 11 Solvent Family 12 Solvent Family 13 Solvent Family 5 Solvent Family 14 Solvent Family 2 Solvent Family 3 Solvent Family 4 Solvent Family Solvent Family 6 Solvent Family 7 Solvent Family 8 Solvent Family 9 Figure 6: Solvent Family Interaction on Water Soluble Soils Water soluble flux residue #2 was easily dissolved in many of the solvent families while Water soluble flux residue #1 was less dispersive in a number of the solvent families. The data indicates that water soluble paste #1 will be more challenging to clean. Tin-Lead No-Clean Solder Paste Flux Residues The solubility parameter for tin-lead no clean solder paste #1 had a high dispersive value, low polarity value and moderate hydrogen bonding value. The solubility parameter for tinlead no clean solder paste #2 had a moderate dispersive, low polarity and low hydrogen bonding values. Figure 7 provides a view of the solvent families that were effective at dissolving the flux residues from these two tin-lead no clean solder pastes. 11

12 Interaction Plot for Tin-Lead No-Clean Solder Pastes Data Means 6 5 Soil Tin-Lead No Clean 1 Tin-Lead No Clean 2 Mean Solvent Family 1 Solvent Family 10 Solvent Family 11 Solvent Family 12 Solvent Family 13 Solvent Family 5 Solvent Family 14 Solvent Family 2 Solvent Family 3 Solvent Family 4 Solvent Family Solvent Family 6 Solvent Family 7 Solvent Family 8 Solvent Family 9 Figure 7: Solvent Family Interaction on Tin-Lead NC Soils The solubility properties of the two tin-lead no-clean soils were similar. The data indicates that the cleaning performance for these two soils will be similar. Lead-Free No-Clean Solder Paste Flux Residues The solubility parameter for lead-free no clean solder paste #1 had a high dispersive value, low polarity value and moderate hydrogen bonding value. The solubility parameter for leadfree no clean solder paste #2 had a high dispersive, moderate polarity and moderate hydrogen bonding values. Figure 8 provides a view of the solvent families that were effective at dissolving the flux residues from these two lead-free no clean solder pastes. 12

13 Interaction Plot for Lead Free No-Clean Solder Pastes Data Means 6 5 Soil Lead-Free No Clean 2 Lead Free No Clean 1 Mean Solvent Family 1 Solvent Family 10 Solvent Family 11 Solvent Family 12 Solvent Family 13 Solvent Family 14 Solvent Family 5 Solvent Family 2 Solvent Family 3 Solvent Family 4 Solvent Family Solvent Family 6 Solvent Family 7 Solvent Family 8 Solvent Family 9 Figure 8: Solvent Family Interaction on Lead-Free NC Soils The solubility properties for the two lead-free no clean solder pastes were also very similar. A stark contrast to the tin-lead and water soluble no clean solder pastes is that the lead-free no clean solder pastes were much harder to clean. Solubility testing gives the formulator insight into the make-up of the soil and the forces needed to clean the soil. This data provides insight into the dispersive, polarity, and hydrogen bonding forces needed within the cleaning agent to remove the soil. Other techniques such as FTIR, GCMS, and HPLC can be used to characterize the organic makeup of the soil (Figure 9). 13

14 Figure 9: Utilize FTIR, GC-MS, and HPLV, to Characterize Soil Differences 10 Matching the Cleaning Agent to the Soil The first set of test values found the interaction of different solvent families on the solder paste flux residues in the test matrix. This test provides an overview of aqueous cleaning solvents that rapidly dissolve the soil. Process conditions in the form of VOC content, time, temperature and concentration were tested to determine the optimal condition for removing the soil. The operating premise is that cleaning agents with like properties to the soil will matchup and dissolve the soil. The data findings compare and contrast the static cleaning rate for four aqueous cleaning agents with different levels of VOC. The static cleaning rate was developed on four aqueous cleaning agents. Table 2 lists the cleaning agent properties. The aqueous products are formulated as concentrated engineered compositions designed to be diluted with water. Three concentration levels were tested with three solution temperatures ran at each concentration. The test vehicles were graded using the scale in Figure 3 and Table 1. 14

15 Cleaning Agent Conc. Levels Tested Temp. Levels Tested VOC grams/liter High Solvency/ Low Reactivity 1.) 10% 1.) 20 C 1.) 94 (HSLR) 2.) 15% 2.) 40 C 2.) ) 20% 3.) 60 C 3.) 188 Medium Solvency/Medium 4.) 10% 4.) 20 C 4.) 60.9 Reactivity (MSMR) 5.) 15% 5.) 40 C 5.) ) 20% 6.) 60 C 6.) Medium Solvency/High 7.) 10% 7.) 20 C 7.) 88.9 Reactivity (MSHR) 8.) 15% 8.) 40 C 8.) ) 20% 9.) 60 C 9.) Low Solvency/ High Reactivity 10.) 10% 10.) 20 C 10.) 19.5 (LSHR) 11.) 15% 11.) 40 C 11.) ) 20% 12.) 60 C 12). 39 Table 2: Aqueous Cleaning Factors / Levels Tested ph The main effects plot for the two water soluble lead free solder pastes (Figure 10) provides meaningful process information. Pay attention to the grading scale as described in Table 1. All four cleaning agents are effective at cleaning the water soluble soils including the Low Solvency / High Reactivity cleaning agent that would meet the proposed limit of 25 grams per liter. This is not unexpected since these residues are designed to be cleaned with water only. The question one may ask is why not use water soluble solder pastes on all assembly types. The answer is that water soluble flux residues are highly active, and if left trapped under tight components, dendritic electrochemical migration grows rapidly. The second concern is that water soluble fluxes cannot withstand the added heat need when soldering lead-free alloys on highly dense components circuit designs. Assemblers building high reliability hardware cannot risk highly active fluxes when failure cannot be tolerated. 15

16 Main Effects Plot for Water Soluble Flux Data Means 6 Cleaning Agent Conc. 4 2 Mean HSLR LSHR MSHR MSMR Temp VOC Figure 10: Main Effects Plot for Lead-Free Water Soluble Fluxes The main effects plot for the tin-lead no clean solder pastes (Figure 11) also provides meaningful process information. Pay attention to the grading scale as described in Table 1. The High Solvency / Low Reactivity and Medium Solvency / High Reactivity provided the best static cleaning rate for the two soils evaluated. Cleaning performance improved as the cleaning agent concentration and temperature increased. The data indicates that VOC content in the range of grams per liter provided the best static cleaning rate. 16

17 Main Effects Plot for Lead-Free Tin-Lead Flux Data Means 6 Cleaning Agent Conc. 4 2 Mean HSLR LSHR MSHR MSMR Temp VOC Figure 11: Main Effects Plot for Tin-Lead No-Clean Flux The main effects plot for the lead-free no clean solder pastes (Figure 12) also provides meaningful process information. Pay attention to the grading scale as described in Table 1. The High Solvency / Low Reactivity cleaning agent provided the best static cleaning rate for the two soils evaluated. Cleaning performance improved as the cleaning agent concentration and temperature increased. The data indicates that VOC content in the range of grams per liter provided the best static cleaning rate. 17

18 Main Effects Plot for Lead-Free No-Clean Data Means Cleaning Agent Conc. Mean HSLR 20 LSHR Temp 40 MSHR 60 MSMR VOC Figure 12: Main Effect Plot for Lead-Free No-Clean Flux Solubility testing provides an accurate indicator of soil properties and the forces needed to clean those soils. Documenting these methodologies may be helpful to the commission in your assessment of what is needed for cleaning high valued circuit assemblies. 4.0 Contamination and its Effects on Electronic Assemblies Increased electrical device functionality results from closer spacing between electrical solder connections (cathode and anode) and more functions in a smaller area. Device miniaturization increases the electric field attraction between conductors. Process and service related contaminants accelerate the potential for device failures. Corrosion problems decrease product and reduce functionality. 18

19 Ionic and non-ionic residues can occur from incoming components, soldering, and handling. Ion migration leads to current leakage, galvanic coupling, and formation of electrochemical cells. 6 Cleaning is commonly considered based on the end use environment Military, Defense, Aerospace, Medical, Automotive, Information Technology, and Industrial etc. The design / service life of the product (i.e. 90 days, 3 years, 20 years, 50 year, Life-time) must be considered. The consequence of failure is also a factor (example: cell phone vs. pace maker) when determining the value of cleaning. No-clean soldering materials were introduced as a replacement for ozone depleting cleaning agents in the early 1990 s. The hope was that cleaning could be eliminated as a part of the assembly process. No-clean soldering technology is driven by cost pressures and difficulty of cleaning highly dense printed circuit assemblies. True no-clean processes require stringent controls of all incoming components and their level of cleanliness. All phases of the assembly process must be controlled to prevent ionic contamination. Today, no clean assembly processes are a source of concern within industry especially when coupled with reductions in lead pitch and conductor spacing. New reliability risks are introduced with the move to lead-free technology, new board finishes, exposed copper and silver, tin whiskers, and highly active flux compositions. With higher functioning devices, electronic assemblers are faced with the dilemma of determining the level of cleanliness needed to produce reliable hardware. The question of how clean is clean enough is more challenging to answer as conductors and circuit traces are increasingly narrower. An added problem is that most assemblers have no background in chemistry, chemical interactions, or analytical test methods. Most do not know how to measure or define cleanliness, nor can they recognize process problems related to residues. Figure 1 provides a simplified view of the materials used to build electronic assemblies. 19

20 Figure 1: Electronic Assembly Process Advanced package functionality achieves higher processing using tighter spacing between conductors, higher frequency clock speeds and stacked packages. Contamination from the assembly and joining can facilitate the movement of electrons through adjacent metal conductors. 7 In the presence of moisture from the environment and voltage, metallic filaments can migrate through contamination to cause intermittent device failures. In some cases, the failures will recover and in other cases the device will short and fail. Bump 6 Bump 5 Bump 4 Bump 3 Bump 2 Bump 1 Figure 2: Electromigration in the Presence of Ionic Contamination and Moisture 20

21 Ionic contaminants can facilitate the growth of metal filaments between conductors on the circuit assemblies. The filaments grow from the cathode to the anode. In the presence of atmospheric moisture, ionic contaminants can dissolve metal (cation with a positive charge at the anode) at one of the conductors and be transported through magnetic attraction when powering up the device with electrical voltage (Figure 3). Figure 3: Electrochemical Migration One of the cleaning challenges is that over the past 10 years, the size of electronics has reduced by over 70%. Integrated circuits have reduced by over 90%. Constant voltage rises inversely with conductor spacing. As the distances between two oppositely charged conductor s decreases, time-to-failure decreases. The reason is that contamination has a less distance to migrate. The trends toward miniaturization increase the importance on cleaning. 5.0 Five Cleaning Forces Five forces that directly influence electronic assembly cleaning properties are the solder flux, heat exposure, component gap, cleaning agent, and cleaning equipment. 9 Variations in any of these factors can and does influence the cleaning rate. Soldering Flux Solder alloys rapidly oxidize upon exposure to air, moisture, and heat. 10 Oxidation is caused by exposure to oxygen in air, which results in a non-conductive and non-solderable metallic surface. Solder flux is a chemical cleaner that removes oxidation form metal surfaces, facilitates wetting, and improves metallurgical bonding. When flux is heated, low boiling 21

22 constituents within the flux evaporate, flux activators remove surface oxidation, and oxygen barriers (rosin/resins) protect the alloys from re-oxidation during the solder process. During the soldering process, heating and cooling ramp rates must be compatible with the assembly and components. The time of exposure to high temperatures must be defined and maintained. Flux and cleaning agent advances of the past 20-years have kept pace with component and board assembly technology advances. Rosin, low-solids, no-clean, and water soluble flux technologies designed for eutectic tin-lead were readily cleanable even after multiple soldering processes. The same cannot always be stated for lead-free soldering. Miniaturization and lead-free soldering require more active and stable flux compositions that remove oxidization with less flux, wet higher surface tension alloys, and protect the underlying metal from oxidation during the soldering process. The cleaning properties of lead-free flux compositions, including water soluble, have changed. The residues are harder and require more active cleaning agents and mechanical to remove the flux residues. Heat Exposure The reflow process heats the circuit board plus components held by solder paste through successively higher temperatures. The solder profile progressively starts by evaporating flux volatiles, initiates flux activation, raises the components to be joined to a temperature which is sufficiently consistent for the solder to flow evenly onto all surfaces, and reflows the solder paste over board finishes to facilitate solder connections. Temperature excursions and the time exposed to liquidus solder temperatures influence cleaning properties. The soldering process can be affected by the mass of the associated component, proximity and mass of neighboring components, the size of the pads, and the amount of heat that travels through the tracks and boards. 11 These factors increase demands on the flux, which has a significant influence on quality and low defect soldering rates. This task becomes more difficult with highly dense miniaturized designs and lead-free soldering. To address these complexities, the flux must be stable to high temperatures; resist charring, oxidation and 22

23 burning; and provide a resistant oxygen barrier. 11 These properties change the solubility and cleaning properties of flux residue post soldering. Component Gap Component miniaturization decreases the spacing between conductors. 13 During solder reflow, flux under fills the bottom side of the component (Figure 4). The distance from the board surface to the bottom side of leadless components is consistently less than 2 mils. For cleaning to occur, the cleaning agent must first wet the residue. To sufficiently wet the residue, the cleaning process must break through the flux dam to create a flow channel. Flux Residue Figure 5: QFN Component with Less 2 mils Gap Cleaning under low gap components is increasingly more difficult due to the higher molecular weight non-polar covalent resins being formulated into lead-free flux compositions. With clearance gaps under components of less than 2 mils, and for small chip caps, gaps less than 1 mil creates a highly difficult cleaning challenge. Cleaning Agent The critical differentiator for removing higher molecular weight flux residues is the cleaning agent. The ideal cleaning agent is formulated with the greenest environmental properties 23

24 within performance limitations; rapidly dissolves polar protic, dipolar aprotic and non-polar soils; and is easily rinsed leaving an ionic cleaned assembly. Since flux residues are a composition of rosin, resins, activators, rheological additives and reacted ionic salt forms, the cleaning agent requires a composition of materials that remove polar protic soils, dipolar aprotic soils, and non-polar resins. Aqueous cleaning agents can be engineered with materials that target ionic, polar covalent and non-polar covalent materials found in the flux residue. Optimal cleaning agents requires a range of materials that solvate non-polar solutes (organic phase) and water soluble solutes with polar and hydrogen bonding forces to solubilize ionic residues (oxygenated and inorganic phase). Using a combination of hydrophobic (oil loving) and hydrophilic (water loving) materials, an aqueous material can be designed to remove electronic assembly soils. Cleaning Equipment With lower component heights, the cleaning equipment must deliver the cleaning agent to the flux residue. Visible flux residues on leaded devices are typically not an issue to clean. The issue is cleaning flux residues under component gaps on leadless components. To remove flux residues under component gaps on leadless components, cleaning equipment designs that deliver the cleaning agent to the source of the flux residue using spray in air are commonly used. Typical spray-in-air cleaning machines are equipped with spray nozzles that hit the board surface and then deflect to move the cleaning agent to the residue. Engineering controls can be used to condense and recover both exhaust and effluent streams. Summary of 5-Cleaning Forces Variability in the five cleaning forces impacts cleaning consistency. Understanding the five cleaning forces and how they apply to a particular cleaning process differentiates a process that meets the cleaning objective versus one that fails to meet the process objective. 24

25 Each of the 5-forces are multi-faceted and must be studied to understand their influence on cleaning the flux residue from under leadless components and then integrated to achieve process consistency. Failure to consider each of the 5-forces when designing the cleaning process often leads to a poor cleaning process. 6.0 Comments to the OTC Model Rule for Solvent Degreasing 2011 a. Solvent Degreasing: The term Solvent Degreasing closely relates to a vapor degreasing process composed of solvent related raw materials. In an effort to clarify the rule intent, would it be more appropriate to rename to: OTC Model Rule for Industrial Cleaning Processes 2011? b. Exemptions under a State Version of the 2001 Model Rule: Electronic Assembly including integrated circuits makes up one of the largest industries worldwide. The complexity of these devices and within industries where failure must be avoided at all cost, an exemption for this industry segment under the 2001 model rule is requested. Affected industry segments should include Aerospace, Military, Defense, Medical Automotive, Industrial, Information Technology, and Telecommunications. c. Specifically, what does the 2001 rule mean? I did not locate the rule on the OTC website. d. How are Low Volatility Solvents considered under the 2011 Model Rule? e. Section 3.0 a & b: A VOC content of 25 grams/liter for batch and inline cold (aqueous) cleaners used for cleaning electronic assembly flux residues is inoperable. A workable limit for removing electronic assembly flux residues using Low Volatility Solvents in Water is roughly 150 grams/liter. f. Section 3.0 c: One alternative is to allow the use of engineering controls on cold cleaners that adsorb or condense VOCs to the design limit but allow the use of aqueous cleaners with high levels of VOCs present up to the limit of 150 grams/liter. g. Section 7.0: Please consider an exemption for the following industries who produce electronic hardware: 1. Military/Defense, 2. Aerospace, 3. Medical, Automotive, 4. 25

26 Telecommunications, 5.Networks and Information Technology, 6. Industrial Controls, 7. Mobile Devices. 7.0 Aqueous Cleaning Processes Over the past 10 years, there have been significant advances in aqueous cleaning agents and cleaning equipment for cleaning electronic assemblies. Formulations with less than 25 grams / liter VOC do not match up well with the common flux types used to assemble printed circuit boards. Low volatile oxygenated solvents have been successfully combined with water for cleaning the residue types present when assembling printed circuit boards. To achieve the desired effect, the formulation requires a combination of dispersive (solvency), polarity, and hydrogen bonding forces. Supplementing the solvency with inorganic builders, bases, and / or acids creates significant material compatibility, reliability and subpar cleaning concerns. Allowing up to 150 grams / liter of low volatility solvents provides formulation flexibility for meeting electronic assembly cleaning needs. 8.0 Exhaust Engineering Controls Technologies are available to condense water liquid vapor from aqueous cleaning processes. Inlet diverters can be used to drop out large water vapor droplets. Gravity separation of smaller droplets can be recovered using demisting technology. One option is to allow a higher VOC limit as requested to 150 grams / liter when exhaust engineering controls are implemented to reduce emitted VOCs at a pre-specified level. 9.0 Conclusion Proper cleanliness levels on printed circuit boards have become more difficult to achieve. Aqueous engineered cleaning agents designed with low volatility oxygenated solvents combined with functional additives clean electronic assembly soils without damaging 26

27 component hardware. They cleaning agent is used in low dilutions in water. Effective levels are workable in the range of 150 grams per liter. We ask for the commission s consideration in placing an exemption for electronic assembly hardware cleaning that allow a VOC limit up to 150 grams per liter when engineered with low volatility oxygenated solvents and used in cleaning equipment with engineered controls for condensing emissions to a predetermined level References 1. Bixenman, M. & Zhang, P. (2011). Scientific Methodologies used to select the Best Cleaning Agent. SMTA China South Shenzhen Conference. 2. Stach, S. & Bixenman, M. (2004, Sep). Optimizing Cleaning Energy in Batch and Inline Spray Systems SMTAI Technical Conference. Donald Stephens Convention Center, Rosemont, IL. 3. Burke, J. (2011). Solvents and Solubility. Handbook for Critical Cleaning, CRC Press, Second Edition. Barbara and Ed Kanegsberg Editors. 4. Minizari, D., Jellesen, M.S., Moller, P., Wahlberg, P., & Ambat, R. (2009, Sep). Electrochemical Migration on Electronic Chip Resistors in a Chloride Environment. IEEE Transactions on Device and Materials Reliability. 9(3), Mackie, A. (2009). Electromigration: Our mutual Friend. SMTA Wafer Level Packaging Conference. Santa Clara, CA. 6. IPC (2007, April). Guidelines for OEMs in Determining Acceptible Cleanliness Levels on Unpopulated Boards. IPC, Bannockburn, IL. 7. Pippen, D.L. A Primer on Hand Soldering Electrical Connections. New Mexico State University. 8. Tarr, M. (n.d.) Wave Soldering. Creative Commons Attribution Non Commercial ShareAlike IPC (2011). IPC-CH-65B Guidelines for Cleaning of Printed Boards and Assemblies. IPC Association for Connecting Electronic Industries. Bannockburn, IL. 27

28 10. Bixenman, M., Northrup, M., Buchan A., Russeau, J. & Jensen, T. (2011). Cleaning in an HDI World. IPC Midwest. Schaumberg, IL Mike Bixenman Qualifications Mike is one of the joint founders and CTO of. He is an active researcher and innovator in the precision cleaning field. Mike chaired the IPC-CH-65B Guidelines for Cleaning Printed Circuit Assemblies released in July 2011 and IPC-7526 Stencil Cleaning Handbook. He has published over 100 research articles on the topic of precision cleaning. Mike holds four earned degrees, including a Doctorate of Business Administration from the University Of Phoenix School Of Advanced Studies. Sincerely, Mike Bixenman, D.B.A. 28