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Technical & White Papers

Validity of the IPC R.O.S.E. Method 2.3.25 Researched

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Abstract: "Miniaturization and higher functionality in electronics packaging require the use of advanced packages and small components. This trend has translated into the use of new package types such as Quad Flat Pack - No Lead (QFP) (also referred to as Leadless Plastic Packages), increased use of chip scale packages as well as increased component density and tighter PCB layouts. Advanced package innovations and new flux types may compromise the validity of the R.O.S.E. cleanliness testing method. This paper researches the effectiveness of the R.O.S.E. cleanliness testing process for dissolving and measuring ionic contaminants from boards soldered with no-clean and lead-free flux technologies. The paper researches quality assurance and process control improvements needed to clean, extract, and measure the resistivity of solvent extract on today's circuit assemblies."

Ionic Cleanliness Testing Research of Printed Wiring Boards

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Abstract: "Ionic Cleanliness testing machines are designed to determine the total ionic content extractable from the printed wiring board for purposes of process control. The conductivity of the extract solution is measured and the results are expressed as sodium chloride equivalence per unit area. The problem with this method is two fold: 1.) Many of today's low residue flux and lead-free flux residues are not soluble in the extract solution. 2.) Contamination of concern is with site specific components, from which contamination does not correlate to the area of concern. The purpose of this study is to research low residue and lead-free flux structures, identify solvent compositions that will dissolve these residue types, and offer options for performing both bulk and site specific ionic cleanliness testing methods."

Versatility of Vertical Format Stencil Cleaners

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Abstract: "The stencil cleaner can be one of the most versatile tools on the manufacturing floor. It can be used to clean electronic modules in various stages of the manufacturing process. In fact, an automated stencil cleaner can clean just about anything you come up against in your PCB assembly process.

Detailed in this paper are seven applications that were submitted to our applications lab providing support to the statement that there is very little that cannot be cleaned in a automated, vertical format, stencil cleaner."

Using Hansen Space to Optimize Solvent Based Cleaning

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Abstract: Sometimes you just cannot clean with water. Good examples of this are: circuits with batteries attached, cleaning prior to encapsulation, ionic cleanliness testing, and non-sealed or other water sensitive parts. High impedance or high voltage circuits need to be cleaned of flux residues and other soils to maximize performance and reliability and, in these types of circuits; water can be just as detrimental as fluxes. When solvent cleaning is called for, Hansen solubility parameters can help target the best solvent or solvent blend to remove the residue of interest, and prevent degradation of the assembly being manufactured. In short, using this approach can time, manufacturing cost and reduce product liability."

Thermal Residue Fingerprinting

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Abstract: "During the last 5 years, the processes to remove flux residues especially for lead-free and challenging geometries have demonstrated new cleaning obstacles which have to be overcome. A new methodology has been recently developed to further increase the propensity for successful cleaning. At the core of this method is the thermal identification of the residue matrix. Thermal energy changes the physical state, i.e. transitions between liquid, solid and gas phases. By taking advantage of such specific information during phase transitions, the cleaning process can be tailored to such settings, which in turn increases the cleaning success significantly.

Thermodynamic data from differential scanning calorimetry (DSC) will be presented in conjunction with experimental data obtained from subsequent cleaning trials in spray-in-air batch cleaning systems. Flux systems that were investigated during this initial study including rosin-based and No-Clean fluxes. A correlation between phase transition temperatures of reflowed flux residues and optimized cleaning parameters for each flux will be presented.

This approach is revolutionary in that it offers completely new, previously untapped avenues to clean challenging electronic assemblies. It also offers insight to previously set process limitations on process temperatures that might have to be reconsidered."

Fluid Flow Mechanics: Key to Low Standoff Cleaning

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Abstract: "In recent years, various studies have been issued on cleaning under low standoff components; most however, with incomplete information. It is essential to revisit and describe the latest challenges in the market, identifying obvious gaps in available information. Such information is crucial for potential and existing users to fully address the cleanliness levels under their respective components. With the emergence of lead-free soldering and even smaller components, new challenges have arisen including cleaning in gaps of less than 1-mil.

This study was initially designed to investigate the impact of mechanical vs. chemical energy contributions during the removal of contamination under 1-2 mil standoff components. To validate the results obtained, extensive studies were conducted, specifically prepared test-assemblies, iterative experimentation, as well as new mechanical innovations that might help users in the future. The latter include, but are not limited to, various flow pattern designs and industry-leading cleaning agents. As a result, the authors will also include experimental data to address fluid flow mechanics, temperature and solvent concentration-related effects.

Initial results obtained indicate that cleanability of residues under low standoff components has become a non-trivial issue. Not only are residues becoming harder to remove, the penetration of the cleaning agent seems to be in direct relationship with the geometry and height of the components in question."

Development and Validation of a New Cleaning Test Platform

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Abstract: "Innovative electronic assembly designs strive to increase functionality over smaller surface areas. Highly dense circuit assembly designs increase the cleaning challenge. Understanding the balance between static chemical and mechanical driving forces is fundamental to predicting and optimizing process variables.

The objective of this research is to improve the science of cleaning under low standoff components. The research will encompass three designed experiments to study nozzle designs, test simulations, and verification in industry standard cleaning equipment. Phase I of this research studies nozzle design cleaning effects for penetrating and removing flux residue under low standoff components. The nozzle cleaning effects were studied using a Cleaning Analyzer Recording Lab that provides video evidence of six different nozzle types.

In this study, two industry suppliers with the cooperation of industry experts at Lockheed Martin seek to understand impingement and fluid flow effects for penetrating and removing flux residue under low standoff components. The testing was done on glasssubstrates that were bumped using anisotropic epoxy. Glass slides were placed over the die. High solids flux residue was dispensed and reflowed using a ramp to spike Pb-free profile. The test simulations were videoed to learn the fluid flow characteristics required to penetrate and remove flux residue under low standoff components."

Cleaning Under Flush Mounted Caps

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Abstract: "Removal of flux residue under highly dense chip caps presents a difficult cleaning challenge. Chip caps are flush mounted to the circuit card. Upon reflow, flux residue fills the gap under the chip cap. Cleaning fluids must wet, dissolve, penetrate the flux dam, and flow under the component to adequately remove all flux residues. Increased board density, miniaturization, and Pb-free soldering magnify this problem. To address this problem, process parameters in the form of cleaning temperature, time, cleaning chemistry concentration, and impingement energy must be considered. This paper presents the results from a designed experiment of an advanced cleaning fluid combined with an optimized inline spray-cleaning machine for removing flux residue under flush mounted chip caps."

Optimizing Cleaning Energy

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Abstract: "The cleaning industry is constantly challenged to improve cleaning processes, staying ahead of the ever-advancing technology curve as it applies to new fields of application. Processes are commonly represented as mechanical and chemical energy, temperature and time. With increasing complexity of board and component geometry coupled to more difficult solder paste and flux formulations, cost of ownership concerns reduce the ability of temperature and time to be effective process variables. As a result, mechanical and chemical energy must make up for reduced temperatures and shorter process times.

Typical approaches to increasing mechanical and chemical effectiveness are counter productive for cost of ownership concerns and achieve only diminished returns. New approaches to mechanical energy are introduced in a way to deliver performance at the heart of the residue, rather than the tail of the delivery system. Coupled with new formulations, which are optimized for lower temperatures of operations, new levels of performance, cost modeling, and throughput are achieved simply by answering these following questions with a thoughtful perspective. What spray configuration is needed at the board level? What type of impingement pressure is needed at the board level? Which is better, high pressure or high flow? All driving towards a single question, is it possible to define a physical equation to determine impingement pressure to penetrate under densely populated components?"

Optimized Spray-in-Air Cleaning

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Abstract: "At the SMTA 2004 tech forum, Stach & Bixenman (2004) presented research for optimizing cleaning energy in batch and inline cleaning systems. The research questions for the 2004 study asked: What equations define surface energy at board level? How does this energy affect the fluid delivery design in a cleaning system? How much impingement pressure is needed at the board level? Which is better, high pressure or high flow? Defining an optimized electronic assembly cleaning system requires an understanding of the balance between the static (potential) and dynamic (kinetic) energies to achieve maximized cleaning performance. Attributes or characteristics that influence cleaning performance center around surface energy, surface tension, capillary action, spray nozzle design, equipment design, time, temperature, and cleaning chemistry.

Phase II of this research test the process cleaning rate equation, which equals the static cleaning rate (chemical forces) plus the dynamic cleaning rate (mechanical forces) using spray-in-air cleaning equipment. The baseline for this experiment establishes the solubility rate of the cleaning solution, at static conditions, to determine the dissolution rate of flux residue, at a pre-determined cleaning chemistry concentration and temperature. Once the cleaning rate is known, how will it be improved by applying physical energy to the board surface? The designed experiment will test the effect of energy applied to the board surface by varying pressure at the board surface. The study’s hypothesis infers that a known dissolution rate and a known surface energy configuration allows an equation to calculate cleaning time and distance. The response variables will be video imaging of the actual cleaning tests, and removal efficiency using ultraviolet detection of residue under low standoff test vehicles. Independent variables consist of substrate standoff heights, cleaning temperature, and cleaning time with various attributes. Constants include fixed amount of nozzles per square inch, predetermine maximum force that does not result in component marking damage, and chemistry concentration."

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Mega™ II - Application Report

Characterization of Primary Solvents for use with the Mega II automated batch cleaning system.

Application Page