SMT Laser Rework on the Horizon
The Advanced Process Laboratory was given an early look at a tool now in development for laser rework of surface mount components. The tool uses an incident beam of infrared laser light to reflow the solder connections of individual SMT components for either removal or reattachment. Custom optics allows the laser beam to be modulated into rectangular shapes of uniform intensity that match the dimensions of the target component. The resultant heating is intense and highly localized, minimizing the risks of solder reflow in neighboring components. After defective component removal and conventional site dress, replacement components are placed with a vacuum pick head followed by reflow attachment with the incident laser.
The APL ran instrumented rework trials for both perimeter and full array BGA components. Resultant solder joint quality was monitored along with careful inspection for damage to the underlying circuit board. A detailed summary has been prepared for AREA Consortium member companies. APL feedback will be the basis for further engineering enhancements before this laser tool becomes generally available.
APL recognized at Cornell University for Innovative Research
At the Annual MSE Awards Gala recently hosted by the Cornell University Materials Science Department our 2018 student intern was recognized for his innovative assembly research in the APL.
At the close of each academic year, the Cornell Materials Science and Engineering department (MSE) hosts an awards dinner, inviting a broad spectrum of its students who are actively involved in materials research to present summaries of their research to visiting industry representatives. Their research posters are judged by a team of Cornell MSE faculty and select industry professionals. Mukund Ayalasomayajula, a Master of Engineering student who served as an on-site graduate research assistant for the AREA Consortium was judged to receive the Master of Engineering Project Innovation Award. His thesis project, executed in the Universal Instruments Advanced Process Laboratory, was described in his poster entitled: Processing of Flexible Electronics using Asymmetric Heating. Under the mentorship of AREA staff researcher Peter McClure, Mukund devised methods to create flipchip solder connections to various flexible substrate materials that are incapable of tolerating conventional flipchip soldering without thermal damage. Viable manufacturing methods for low cost, low temperature polymer materials such as polyethylene terephthalate (PET) and thermoplastic polyurethane (TPU) are critical for enabling the rapidly growing flexible hybrid electronics market. This APL manufacturing research was done in collaboration with NextFlex, one of the federally funded National Network of Manufacturing Institutes tasked with promoting innovation for domestic manufacturing.
Key to the project success was the ability to define and accurately produce solder reflow profiles under controlled thermal gradients provided by the Fineplacer Pico bonder supplied to the APL by our industrial partner Finetech.
AREA Consortium Metallurgical Research featured at TMS 2019
Examples of AREA Consortium Pb-free solder research were featured at the world’s premier annual gathering of metallurgical expertise: TMS 2019. Detailed microstructural investigations are fundamental to all Consortium studies of solder interconnects. Decades of such work have contributed to an extensive metallurgical understanding of solder reliability behavior. Metallurgical observations from two recent consortium research projects were shared in papers presented in the ELECTRONIC MATERIALS track of the 148th annual meeting of TMS in San Antonio, TX.
Effect of Reflow Profile on Microstructure and Mechanical Properties of Low Melting Alloy (SAC/SnBi)
by Mohammed Genanu, et al
The Thermomechanical Reliability at High Temperatures of Pb-Free Solders
by Faramarz Hadian, Harry Schoeller, and Eric Cotts.
These papers were authored by two of the more experienced APL graduate research assistants from the Binghamton University Physics Department. The topics illustrate the full scope of APL assembly interest and expertise, from low temperature assembly processes designed to minimize package warpage to high temperature soldering processes designed to provide robust connections in elevated temperature applications.
Akrometrix upgrades APL Shadow Moiré Interferometry Capability
Akrometrix, a leading industry provider of warpage and strain metrology instruments, has partnered with the AREA Consortium to enhance the APL capability for full-field measurement of temperature induced distortion. The Akrometrix TherMoiré PS200 has been a long-time APL workhorse instrument for monitoring package warpage and other temperature induced board assembly distortions encountered in the course of consortium component assembly studies. Akrometrix recently came on-site in the APL to provide us a complete instrument overall, upgrading our capability to that of their latest TherMoiré PS200S model. This generous enhancement included a new camera, computer, monitor, and 200LPI diffraction grating along with a complete overhaul of the heating stage. Importantly, the upgrade also included installation of the latest Studio fringe analysis software with a full suite of analysis options.
Sintering Copper Interconnects in Formic Acid.
Recognizing the growing need for higher power capability device interconnects, high-end device manufacturers are actively exploring the possibility of all-copper package interconnects. Electromigration resistant copper interconnects can be made using a flipchip dipping process with a copper sintering paste. Subsequent copper sintering to the carrier pad requires a carefully controlled reducing atmosphere. Preparing for member driven evaluations of such copper sintering systems, the APL has constructed an experimental apparatus for the sintering of copper in a formic acid environment. It will be used for studies of copper sintering kinetics and interfacial bond integrity as a function of time, temperature and pressure.
The Advanced Process Lab goes back to School
Graduate student interns in the Advanced Process Laboratory are given a broad exposure to many timely topics in assembly materials, electronics manufacturing and interconnect reliability. More importantly, their individual research assignment provides them an in-depth understanding of some specific technology element. Our most recent intern, Mukund Ayalasomayajula, completed a yearlong assignment studying the properties and performance of various state of the art thermal interface materials used to attach and promote heat flow into heat sinks. Afterward, he returned to Cornell University to complete the required coursework for a Master of Engineering degree in Materials Science and Engineering. After presenting his APL research activities to AREA consortium member companies on several occasions, Mukund was well equipped to lecture his fellow students on key elements of thermal interface technology as well as his own research contributions: https://cornellmengineering.wordpress.com/2019/02/07/making-electronics-more-reliable/amp/An Electrovert Aquastorm 50 batch cleaner recently installed in the APL enables the use of water soluble solder paste formulations in your build requests. High voltage or high frequency applications can be intolerant of flux residues remaining on the assembled board surface and so will often be specified as water wash solder paste assemblies. Our Aquastorm 50 is most often configured for a deionized water wash process to clean such water soluble assemblies. This batch cleaner is however also capable of using various commercial cleaning formulations necessary for removing more tenacious No-clean paste residues.
Finetech Partners with AREA Consortium for Precision Assembly.
Aware of the scope of APL joining research for microelectronics packaging applications, Finetech has selected the FINEPLACER® Pico ma bonding system for installation in the UIC advanced process laboratory. The Pico is a versatile bonding platform suitable for a wide range of micro assembly applications such as high accuracy die attach or the assembly of components requiring novel bonding parameters. It provides a placement accuracy of 5 µm with a straightforward bonding profile definition and supports bonding forces up to 700N.
The versatility of the Pico bonding system has proven ideal for the full range of packaging assembly challenges routinely tackled in the APL. It is critical to the execution of numerous AREA Consortium research projects; including controlled silver sintering for power devices, low temperature joining for flexible hybrid electronics and precision thermo-compression bonding of fine pitch copper pillar interconnects with large die. Its precise control of heating rates and thermal gradients also make it valuable for careful investigations of joining material responses and defect formation mechanisms. It is available for demonstration to all AREA members and APL customers on request.
Engaging the Electronics Assembly Community.
AREA consortium assembly research is executed for the benefit of our member companies with all results and supporting data archived for on-demand access by the membership. Key observations are routinely selected from this growing archive for sharing with the industry at large. Recent examples include the following topics presented at the 2018 SMTA International conference:
Session HE1. Predicting Component Life for Harsh Environments
Pam Lembke: Testing and Mitigating Resistor Silver Sulfide Corrosion
Session APT4. Board Level Reliability
Reza Ghaffarian: Characterization of SiP Assembly and Reliability under Thermal Cycles
Session LF2. High Reliability Pb-free Alloys, SAC305 and Beyond
Lars Bruno: Effect of TIM Compression Load on BGA Reliability
Thank you to these APL industry collaborators for being the public face of our consortium and making these valued contributions to the industry literature.
BTU Pyramax ‘Vacuum’ installed in the APL.
BTU International installed the first of its Pyramax Vacuum reflow oven product line in the APL for solder reflow studies to be shared with AREA consortium members. This oven operates like a standard convection reflow oven but includes an automated vacuum chamber in the hot zone capable of evacuating the ambient pressure down to 1 Torr. Consortium sponsored reflow experiments include evaluations of vacuum level and vacuum hold time and determine how these parameters quantitatively affect solder joint voiding and defect generation in test components such as QFNs and CSPs of varying sizes. The vacuum process parameters required to achieve the desired void reduction varies significantly with package size and format.
Electronics Upgrade for APL Thermal Rod Tester.
A unique APL thermal rod tester is routinely used to measure unit area thermal resistance and thermal conductivity of various thermal interface materials (TIMs) for AREA consortium members. Sample TIM bondlines of accurately controlled thickness are fabricated between aluminum rods. A steady state heat flow is established through the TIM bondline by holding a fixed rod temperature above the bond and a 5°C reduced rod temperature below with a Peltier cooler. This workhorse instrument was recently upgraded with a new control computer, new digital source meters, and platinum resistance temperature detectors (RTDs). The newly refreshed apparatus provides a one sigma measurement uncertainty of 3% in the range of 30 to 130°Cmm2/W. Consortium member companies are welcome to suggest thermal interface materials for evaluation.
Fast and Local—Reflow Where You Need It.
A developmental laser selective reflow soldering tool is now operational in our assembly laboratory. In this custom tool, localized solder reflow is accomplished through the controlled impingement of a 980nm (IR) laser. Custom beam shaper optics redistribute the Gaussian spot beam to a user selected, uniform rectangular area beam. This selectable incident area ranges from 4x4mm to 100x200 mm. Beam power is controlled from 50 to 2000W. We will be exploring process capabilities of this technology within the 2017 consortium research portfolio. The tool is however also available for product specific assembly trials by our customer community. Suggestions for novel joining materials or processes enabled by this technology are welcome.
Constant Current Power Cycling On-line.
Our custom design power cycling system is now on-line and functioning. Sixty four channels of precision controlled constant current sources can be run with a user defined square wave to produce internally generated temperature cycles. All channels are monitored for electrical failures using event detection circuitry as well as analog recording of net resistance drift. MLF80 packages powered to 125C peak temperature have been chosen for the first power cycle reliability test.
Now Heating with Ten Zones.
The APL is the proud owner of a new BTU Pyramax 125N convection reflow oven. This unit was recently installed in our third SMT line. In addition to ten zones of temperature control it offers us a wide rail spacing for 18”x 24” server board reflow and 350C maximum temperature for high temperature electronic assembly. We can now apply some real heat to your toughest reflow jobs.
Defense Against Electronic Failures. The Department of Defense Executive Agent for Electronic Interconnect hosted a roundtable discussion immediately following the APEX equipment show in March.
A key objective of the meeting was to assess the potential contributions of various electronic industry consortia in addressing the reliability concerns of the DoD. Dr. Denis Barbini represented our own AREA Consortium in this venue, reporting back that the skills and tools we bring to bear on our member inspired research projects align quite well with the current DoD needs and challenges.
Paste Printing 101. We hosted our mid-year consortium project update meeting at the end of June. Attending members were treated to the usual progress updates for key research projects but this year’s agenda included a marked emphasis on paste printing studies. Most notably was a long-running APL study to determine dynamic feedback algorithms for manufacturing printer control. Other topics included reliability consequences of isolated underprints, aperture placement limits for stencil patches and new paste material evaluations. There was even some printing trials for automated assembly of sintered silver paste materials.
Feeling the Power. The design of our new power cycling test apparatus has progressed to the prototype stage. A simple two channel prototype board has demonstrated cyclic current induced heating of SMD 1206 resistors over an extended period. The circuit board design for the final power cycle apparatus is being routed now. It will boast eight test channels, each with cyclic control of a constant test net current, electrical event detection and circuit resistance logging.
You Can Observe a lot by Just Watching. Following some well-known advice from baseball sage Yogi Berra, we are now observing the dynamics of BGA solder joint formation using our new MetCal side view camera. This camera system is now operational on our OKi Scorpion hot gas rework tool. It can record soldering events with real time video as well as capture high magnification still photos of reflow events under the rework nozzle.
No Fly Zone for Pb-free Solder. We were invited to meeting #27 of the IPC PERM Council recently held in Phoenix, AZ. This distinguished group of military/avionics electronics experts was specifically interested in the scope of AREA Consortium research addressing the reliability of Pb-free solder assemblies. Highlights of the experimental approaches we use for evaluating Pb-free solder alloys in the APL were shared in the following talk:
“Evaluating Alternative Pb-free Solder Alloys”
by B. Arfaei and J. Wilcox
At our regular consortium meetings, our members routinely see all the data generated from these laboratory methods for many member proposed alternative alloy soldering systems.
Boards, Boards and more Boards! Some customization of our large Thermotron F110 environmental chamber was required to accommodate our ambitious 2016 alternate solder alloy evaluation project. The improved temperature uniformity from two added auxiliary heater units has increased the functional capacity of this chamber by 30%. This extensive alloy reliability project includes five new solder alloys along with the common alloys (SAC105, SAC305, SnPb eutectic) acting as controls. A massive wiring effort by our intrepid graduate student team prepped several hundred test boards for electrical monitoring.
More than 100 boards are now cycling in our newly enhanced F110 environmental chamber.
Solder Paste Inspection. Consortium member Koh Young Technology has graciously installed their latest Dual Projection SPI tool (model 8030-3) in the APL surface mount assembly line. We are planning a detailed look at the SPI data produced by this new tool. It will be used routinely for all future APL assembly runs and will also play a key role in solder paste printing projects planned for the consortium research portfolio.
Teaching the Next Generation. On December 4th, Universal hosted 75 undergraduate engineering students into the Advanced Process Laboratory for an interactive demonstration of surface mount assembly manufacturing. The students, from the Systems Science & Industrial Engineering department at Binghamton University, were offered live demonstrations of solder paste screen printing, automated component placement and convection reflow soldering. Key manufacturing inspection methods and analytical tools were also reviewed.