News
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.
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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.
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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.
- 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.
- 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.
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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.
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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.
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- 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.
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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.
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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.
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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.
- 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.
- 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
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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.
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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.
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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.
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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.
APL Eventsuic.aplab@gmail.com
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