Recent Publications
The intention of publications made by Atotech is to share the results of our extensive research and development on a non commercial basis. With these presentations we aim to provide in-depth process information and inform about the latest investigations and results in each technology field. It should enable the reader to gain a complete and comprehensive understanding of our process solution and of general phenomena encountered in the electroplating industry.
This segment presents the recent papers from the business technology team final finishing.
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Direct EP and Direct EPAG – Novel Surface Finishes for gold-, copper wire bonding and soldering applications
Mustafa Oezkoek, Atotech Deutschland GmbH, October 2012
The direct deposition of palladium on copper was first introduced to the market as a surface finish on copper by Atotech more than 10 years ago.
Market, technology and environmental requirements in the electronic industry have resulted in reconsidering the direct EP/EPAG finish process as a viable and cost-effective surface finish. This paper deals with soldering on various wire bond tests on the Direct EP and EPAG Finish as well as soldering test results. It shows that the pure EP finish, as environmentally "green" process, and the EPAG finish offer a measurable cost advantage over current standard surface finishes for copper wire bonding.
Download complete paper here: pdf file (File size 200 kB)
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Copper Wire Bonding on pure Palladium Surface Finishes - Eliminating the Gold Cost from the Electronic Package
Mustafa Özkök, Atotech Deutschland GmbH; Hugh Roberts, Atotech USA Inc.; Horst Clauberg, Kulicke and Soffa Industries, Inc. January 2011
During the past two years, fine pitch copper wire bonding has finally entered high volume production. It is estimated that nearly 15% of all wire bonders used in production are now equipped for copper wire bonding. Most of these are used exclusively for copper wire bonding. In terms of pitch, copper wire is only barely lagging behind the most advanced gold applications. The most commonly used copper wire is 20 µm in diameter and 18 µm copper wire is entering final qualification. Evaluations with even finer wire are underway.
Although some technical challenges remain, many years of research have now resolved most of the problems associated with copper wire bonding and attention is beginning to shift from merely ensuring reliable manufacturing processes to optimizing processes for efficiency and throughput. The most advanced wire bonders now have pre-configured processes specifically designed for copper. In addition to throughput optimization, further cost reductions are being sought. Among these is the desire to eliminate the high-cost gold not just from the wire, but also from the substrate.
Download complete paper here: pdf file (File size 200 kB)
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The Benefits of ENEPIG with pure PD for Gold Wire Bonding
Mustafa Oezkoek, Gustavo Ramos, Dieter Metzger, Atotech Deutschland GmbH; Hugh Roberts, Atotech USA Inc., August 2010
As a surface finish, electroless nickel / electroless palladium / immersion gold (ENEPIG) has received increased attention for both packaging/IC-substrate and PWB applications. With a lower gold thickness compared to conventional electroless nickel / immersion gold (ENIG) the ENEPIG finish offers the potential for higher reliability, better performance and reduced cost.
This paper shows the benefits of using a pure palladium layer in ENEPIG and ENEP (Electroless Nickel / Electroless Palladium) surface finishes in terms of physical properties and in terms of gold wire bonding test results.
Download complete paper here: pdf file (File size 370 kB)
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Resistance of common PWB Surface Finishes against Corrosion in Harsh Environments
Mustafa Özkök, Mario Gensicke, Guenter Heinz, Atotech Deutschland GmbH; Hugh Roberts, Joe McGurran, Atotech USA Inc. July 2010
Corrosion resistance is becoming one of the most important topics in the electronics industry. Corrosion results in field failures and huge losses, which annually total several billion U.S. dollars. The actual extent of losses caused by corrosion is not well documented in the industry. As such, corrosion is currently one of the most challenging topics and is acquiring more attention as a result of increased product warranties, new materials and process changes caused by recent legislation impacting the electronics industry.
Depending on the final application and the environment to which the product is exposed, the requirements for corrosion resistance can be significantly different. Products used in military, automotive and medical applications typically demand higher corrosion resistance than products for lower performance or lifetime expectations, such as consumer electronics or similar products used in nonaggressive environments. As a result, to avoid corrosion on electronic products each industry sector has essentially adopted its own reliability testing procedures and standards. These facts all lead to the question, "What is the right corrosion resistance level of the surface finish for a particular product?"
Download complete paper here: pdf file (File size 1000 kB)
Pure Palladium and Palladium Phosphorus Depositions Used in ENEPIG and ENEP Surface Finishes – Comparison of Physical Properties and Their Influence on Soldering and Au Wire Bonding
Mustafa Oezkoek, Atotech Deutschland GmbH; Hugh Roberts, Joe McGurran, Atotech USA Inc., October 2010
As a surface finish, electroless nickel / electroless palladium / immersion gold (ENEPIG) has received increased attention for both packaging/IC-substrate and PWB applications. With a lower gold thickness compared to conventional electroless nickel / immersion gold (ENIG) the ENEPIG finish offers the potential for higher reliability, better performance and reduced cost.
This paper shows the benefits of using a pure palladium layer in ENEPIG and ENEP (Electroless Nickel / Electroless Palladium) surface finishes in terms of physical properties and in terms of gold wire bonding and solder joint integrity.
Download complete paper here: pdf file (File size 466 kB)
Pure Palladium in ENEPIG Surface Finishes - Physical properties of the Pd deposition and their influence on soldering and wire bonding
Bill Kao, Atotech Taiwan Limited; Mustafa Oezkoek, Atotech Deutschland GmbH; Hugh Roberts, Atotech USA Inc., October 2010
As a surface finish, electroless nickel / electroless palladium / immersion gold (ENEPIG) has received increased attention for both packaging/IC-substrate and PWB applications. With a lower gold thickness compared to conventional (ENIG) the ENEPIG finish offers the potential for higher reliability, better performance and reduced cost.
This paper shows the benefits of using a pure palladium layer in ENEPIG and ENEP (Electroless Nickel / Electroless Palladium) surface finishes in terms of physical properties and in terms of gold wire bonding and solder joint integrity.
Download complete paper here: pdf file (File size 315 kB)
Benefits of Pure Palladium for ENEP and ENEPIG Surface Finishes
Mustafa Oezkoek, Gustavo Ramos, Dieter Metzger, Atotech Deutschland GmbH; Hugh Roberts, Atotech USA Inc., September 2010
As a surface finish, electroless nickel / electroless palladium / immersion gold (ENEPIG) has received increased attention for both packaging/IC-substrate and PWB applications. With a lower gold thickness than conventional electroless nickel / immersion gold (ENIG) the ENEPIG finish offers the potential for higher reliability, better performance and reduced cost. Similar advantages appear to be achievable through the use of the electroless nickel / electroless palladium process (ENEP).
Download complete paper here: pdf file (File size 315 kB)
Gold Wire Bonding Performance and Reliability of ENEPIG Surface Finishes
Kenneth Lee, Mustafa Özkök, Atotech Deutschland GmbH; Stefan Schmitz, Fraunhofer IZM Berlin, August 2010
The expression "multifunctional PCB", as a synonym for a PCB which is applicable with a variety of assembly techniques, is already established on the market. That means the PCB can be used for multiple reflow soldering and multiple assembly techniques like, Al-wire bonding, Au-wire bonding, conductive adhesives and other interconnection methods. In the mixed COB/SMT assembly, where mainly Al-wire bonding is used, the ENIG Surface finish with Ni thickness of 5-6 μm and Au thickness of 50 – 100 nm, is a well established surface finish.
But the ENIG surface finish can not be used for Au-wire bonding which is used mainly in the packaging industry. On ENIG sometimes bond Lift off´s were reported that are often caused by an exceeding amount of Ni oxides at the Au surface because of Ni diffusion. At the other side the surface finishes electrolytic Ni/Au or electroless Nickel with autocatalytic gold are working well with Au-wire bonding but because of the high Au thickness that hinders a Ni diffusion for a longer time period. In addition the solder joint integrity thick Au of the surface is not regarded as a reliable material combination because brittle AuSn4 phases are formed.
Download complete paper here: pdf file (File size 400 kB)
ENEP - A Cost-Effective Alternative for High Reliability Soldering Applications
Gustavo Ramos, Mustafa Özkök, Sven Lamprecht, Atotech Deutschland GmbH; Hugh Roberts, Atotech USA Inc., April 2010
Electroless nickel/immersion gold (ENIG) has been recognized within the electronics packaging industry as a reliable surface finish for soldering applications. Unlike surface finishes, such as OSP, immersion silver or immersion tin, which produce a Cu-Sn intermetallic upon soldering, the nickel layer of ENIG acts as a barrier to minimize copper dissolution during the soldering application. This function is especially important for assemblies that require multiple solder reflow steps. However, if not properly controlled, excessive corrosion of the nickel by the immersion gold step can also cause the well documented "black pad" effect, often resulting in solder joint reliability issues, including brittle fracture.
As an alternative to ENIG, an electroless pure palladium layer over the electroless nickel (ENEP) provides a solderable surface without the noted risk of damage to the underling nickel layer. By eliminating the corrosive attack of the gold bath, the final layer stack would be suitable for high reliability soldering involving both IC substrate and PWB applications. In addition, because of the current high price of gold, replacing it with a pure palladium deposit can offer measureable cost savings for the ENEP process in comparison to ENIG.
Download complete paper here: pdf file (File size 1000 kB)
Ageing Characteristics of Immersion Tin Surface Finishes
Sven Lamprecht, Dr. Hans-Jürgen Schreier, Dr. Roland Vogel, Atotech Deutschland GmbH, October 2000
The technology of surface finishes for printed circuit boards is seeing a dramatic shift from the Hot Air Solder Levelling (HASL) towards alternative finishes like electroless Nickel - immersion gold (ENIG), immersion tin, immersion silver and organic solder preservatives (OSP's).
This trend is mainly caused by the worldwide environmental pressure to ban the use of lead for electronic assemblies as well as the demands of modern assembly technology, which require a higher coplanarity of the surface finish for surface mount assembly.
This paper discusses the ageing characteristics of immersion tin surface finishes. Thermal ageing conditions are investigated and correlated with the reliability during soldering operations.
Download complete paper here: pdf file (File size 430 kB)
Immersion Tin and Tin Whisker Growth
Sven Lamprecht, Carl Hutchinson, Atotech Deutschland GmbH, September 2004
The kinetics of whisker growth on pure, electroplated tin layers is known since many years and common knowledge to industry. This whisker effect is being well described in literature and topics of several published papers.
In order to check reliability, in terms of whisker growth, special test methods have been used in industry (e.g. Bellcore – GR-78-CORE/R13.2.7, IPC TM 650 2.6.3.3 and IPC TM 650 2.3.14). Common for those tests are environments with increased temperature (40-85°C) to which the specimens are exposed. These common tests are state of the art and industrial standards.
This paper discusses investigations performed leading to better understanding of the kinetics of tin whisker growth. This whisker effect is being well described, as well as mitigation strategies.
Download complete paper here: pdf file (File size 365 kB)
Study of the mechanism responsible for "Black pad" defect on PWB's using electroless nickel / immersion gold as final finish
Kuldip Johal, Atotech USA Inc., Sven Lamprecht, Atotech Deutschland GmbH, March 2002
Over the past several years there has been consistent growth in the use of electroless nickel/immersion gold (ENIG) as a final finish. The finish is now frequently being used for PBGA, CSP, QFP and COB and more recently gathered considerable interest as a low cost under-bump metallurgy for flip chip bumping application.
The assembly industry over several years has experienced various defects associated with surface finishes. A defect known as "Black pad" has been reported. The exact definition of "black pad" varies from chemical vendor / board manufacturer / assembler and OEM. This adds to the confusion. The defect is quite often mistaken for other defects such as de-wetting due to contaminated ENIG surface, BGA interfacial fracture due to mismatch of thermal expansion coefficient differences between materials or associated with miss registration of soldermask, excessive gold thickness >5 microinches and insufficient or no under fill used. Due to the fact that both defects result in a failed or open solder joint, when the joint is de-soldered the underlying nickel appears black. The "black pad" defect is generally at very low ppm level, due to this low level and the number of variables involved, the root cause has been difficult to find.
In addition to the papers referenced several chemical manufactures / PWB fabricators / Contract manufactures / OEM's have investigated the defect, to give a possible insight to the mechanism.
Download complete paper here: pdf file (File size 440 kB)
Impacts of Bulk Phosphorous Content of Electroless Nickel Layers to Solder Joint Integrity and their Use as Gold- and Aluminum-Wire Bond Surfaces (Best International Paper Award, IPC Expo 2004.03)
Sven Lamprecht, Dr. Hans-Jürgen Schreier, Atotech Deutschland GmbH, Hugh Roberts, Kuldip Johal, Atotech USA, Inc., February 2004
The influence of co-deposited phosphorus within an electroless nickel layer (from low- to high-P) on the reliability of the solder joint integrity and aluminum-wire bond performance was investigated.
Download complete paper here: pdf file (File size 1120 kB)
Electroless Nickel / Immersion Gold Process Technology for Improved Ductility of Flex and Rigid-Flex Applications
Kuldip Johal, Hugh Roberts, Atotech USA Inc., Sven Lamprecht, Christian Wunderlich, Atotech Deutschland GmbH, January 2001
In particular, Young's Modulus (stress-to-strain ratio) is evaluated to show a direct relationship between the phosphorus content of the electroless nickel deposit and the ductility of the overall ENIG finish.
Download complete paper here: pdf file (File size 340 kB)
Electroless Nickel / Electroless Palladium / Immersion Gold Process For Multi-Purpose Assembly Technology
Kuldip Johal and Hugh Roberts, Atotech USA Inc. , Sven Lamprecht, Atotech Deutschland GmbH, September 2004
As the second part to the paper "Electroless Nickel / Electroless Palladium / Immersion Gold Plating Process for Gold and Aluminum-Wire Bonding Designed for High-Temperature Applications", this paper further summarizes the results from technical qualification of the ENEPIG process.
Download complete paper here: pdf file (File size 1440 kB)
Wetting Behavior of Pb-free Solder on Immersion Tin Surface Finishes in Different Reflow Atmospheres
Sven Lamprecht, Günter Heinz, Atotech Deutschland, Dr. Kenneth Lee, Atotech Asia Pacific, Bill Kao, Atotech Taiwan, October 2006
As remedy typically nitrogen atmosphere is used during reflow soldering. By this, the negative impacts of oxidation and tarnishing are minimized, ensuring proper wetting and avoiding discoloration of the surface. On the other hand, nitrogen consumption during reflow is an essential part of the overall cost of the product and a continuous target of cost saving efforts.
Download complete paper here: pdf file (File size 320 kB)
Alternative Nickel-based Surface Finishes for IC Substrate Applications in a Pb-free Environment
Hugh Roberts, Atotech USA, Inc, Sven Lamprecht, Christian Sebald, Atotech Deutschland, March 2008
When properly applied, the electroless nickel/immersion gold (ENIG) process has traditionally been proven to be a reliable finish for soldering applications. Long before the recent migration to Pb-free solders, nickel was recognized as an effective barrier layer to inhibit dissolution of copper during the soldering process. However, the immersion gold reaction can often excessively corrode the nickel layer, resulting in tendencies toward brittle failure in solder joints. In addition, with the inherent higher temperatures, Pb-free soldering on ENIG presents new challenges, such as controlling the growth of certain nickel-tin IMCs, which can further impact solder joint reliability. To address these concerns, recent investigations have been conducted to evaluate the performance of ENIG and ENEP (electroless nickel electroless palladium), both intended for IC substrate applications.
Download complete paper here: pdf file (File size 4.500 kB)
Effect of Process Variations on Solder Joint Reliability for Nickel-based Surface Finishes
Hugh Roberts, Atotech USA, Inc, Sven Lamprecht, Gustavo Ramos, Christian Sebald, Atotech Deutschland, April 2008
This paper summarizes the results of recent investigations to examine the effect of electroless nickel process variations with respect to Pb-free (Sn-3.0Ag-0.5Cu) solder connections. These investigations included both ENIG and ENEP (electroless nickel electroless palladium) as surface finishes intended for second level interconnects in BGA applications. Process variations that are suspected to weaken solder joint reliability, including treatment time and pH, were used to achieve differences in nickel layer composition. Immersion gold deposits were also varied, but were directly dependent upon the plated nickel characteristics. In contrast to gold, different electroless palladium thicknesses were independently achieved by treatment time adjustments.
Download complete paper here: pdf file (File size 4.500 kB)
Electroless Nickel / Electroless Palladium / Immersion Gold Plating Process for Gold and Aluminum-Wire Bonding Designed for High-Temperature Applications
Kuldip Johal, Hugh Roberts, Atotech USA, Inc, Sven Lamprecht, Atotech Deutschland, February 2004
This paper summarizes the results of qualification testing of the Electroless Nickel / Electroless Palladium / Immersion Gold (ENEPIG) process as it may be applied for use in high-temperature functional applications. The effects of exposure to heated, high humidity environments were also examined, in addition to the impact of extended thermal cycling.
Download complete paper here: pdf file (File size 260 kB)
High Phosphorus ENIG – Highest Resistance against Corrosive Environment
Sven Lamprecht, Petra Backus, Atotech Deutschland, April 2003
This paper describes the influence of co-deposited Phosphorus within the Nickel layer, regarding the influence to the ENIG process itself (especially the corrosive attack of the immersion gold reaction) and the survivability of PCBs in corrosive atmosphere. Within this paper, different test methods are described and discussed to check the protective performance of a high Phosphorus ENIG layer.
Download complete paper here: pdf file (File size 300 kB)
Nickel / Palladium / Gold – Chemisches Beschichten für Hoch-Temperatur Anwendungen
Sven Lamprecht, Atotech Deutschland, Kuldip Johal, Hugh Roberts, Atotech USA, Inc., December 2004
Diese Veröffentlichung umfasst Ergebnisse einer Qualifikationsuntersuchungen an einer chemisch Nickel / chemisch Palladium / Sudgold (Ni/Pd/Au) Endschicht, die im Hochtemperaturbereich eingesetzt wird. Während der Untersuchung wurde die Wirkung von ausgedehnten Temperaturwechseltests, als auch die Einflüsse trockner sowie feuchter Wärme untersucht.
Download complete paper here: pdf file (File size 280 kB), German language
Analysis of BGA Solder Joint Reliability for Selected Solder Alloy and Surface Finish Configurations
Hugh Roberts, Atotech USA, Inc, Sven Lamprecht, Christian Sebald, Atotech Deutschland, Mark Bachman, John Osenbach, Kishor Desai, LSI Corporation, Ron Huemoeller, YoonHa Jung, Robert Darveaux, Amkor Technology, March 2009
This presentation summarizes the findings from part of a major ongoing project to evaluate the performance of several combinations of surface finishes (ENEPIG vs. electrolytic NiAu) and solder ball alloys for wire-bond and flip chip BGA package applications, while focusing on the flip chip segment of those investigations.
Download complete paper here: pdf file (File size 2.100 kB)
Performance Evaluations of Surface Finish and Solder Alloy Configurations for BGA Solder Joint Reliability
Hugh Roberts, Atotech USA, Inc, Sven Lamprecht, Christian Sebald, Atotech Deutschland, Mark Bachman, John Osenbach, Kishor Desai, LSI Corporation, Ron Huemoeller, YoonHa Jung, Robert Darveaux, Amkor Technology, February 2009
The paper summarizes the findings from a major ongoing project to evaluate the performance of several combinations of surface finishes (electrolytic NiAu, ENEPIG, Imm. Sn, SOP) and solder ball alloys for wire-bond BGA package applications. In this phase of the evaluation, high-speed ball shear testing was used as the primary methodology for examining 2nd level solder joint reliability. The solder alloys tested included eutectic SnPb, SnAg and SAC305. The concept of "point of inflection" was used to determine the selected shear speeds for each solder alloy; dependent upon a failure analysis screening that was also performed. The evaluation included high-speed shear testing conducted after ball attach, as well as after extended high-temperature storage conditions.
Download complete paper here: pdf file (File size 2.750 kB)
Evaluation of Pb-free BGA Solder Joint Reliability on Ni-based Surface Finishes using Alternative Shear and Pull Metrologies
Kuldip Johal, Hugh Roberts, Atotech USA, Inc, Sven Lamprecht, Thomas Beck, Hans-Juergen Schreier, Christian Sebald, Atotech Deutschland, January 2007
This technical paper summarizes the findings and conclusions from a comprehensive examination of Pb-free solder ball bonding, comparing ball shear and cold ball pull testing results. The paper compares results obtained from conventional (slow) speed ball shear and cold ball pull testing with the results from newer high-speed test parameters. Relationships between ball shear and cold ball pull results are examined. Findings are also compared for two different PWB surface finishes: a process-of-record electroless nickel / immersion gold finish (ENIG), and an electroless nickel / electroless palladium / immersion gold finish (ENEPIG).
Download complete paper here: pdf file (File size 4.930 kB)
Immersion Tin as a Cost-effective and Reliable Surface Finish for Pb-free Automotive Electronics Applications – Phase II Investigations
Elaine Bevan, John Coates, Steve Prosser, TRW Automotive, United Kingdom, Hugh Roberts, Atotech USA, Inc, Sven Lamprecht, Atotech Deutschland, October 2007
This paper summarizes the results of the second phase of a comparative study of immersion tin and immersion silver as a Pb-free surface finish including the results of environmental testing performed under the supervision of the Tier 1 supplier.
Download complete paper here: pdf file (File size 2.830 kB)
Investigation of the Recommended Immersion Tin Thickness for Pb-free Soldering
Sven Lamprecht, Atotech Deutschland, April 2004
This paper describes the different thickness measurement techniques, enabling reliable thickness readings, and the determination of the recommended immersion Tin thickness for Pb-free soldering.
Download complete paper here: pdf file (File size 260 kB)
Performance and Reliability Evaluation of Alternative Surface Finishes For Wire Bond and Flip Chip BGA Applications
Kuldip Johal, Hugh Roberts, Atotech USA, Inc, Kishor Desai, Q.H. Low, LSI Logic, Milpitas, CA, USA, Ron Huemoeller, Amkor Technology, Inc., USA, February 2006
This report summarizes the findings and conclusions from the first phase of a joint project between Atotech, Amkor and LSI Logic. The overall objective of the project is to evaluate reliability of several different surface finishes for both wire bond and flip chip BGA applications with the intention of maintaining or improving performance while achieving manufacturing cost reductions. Because of functional requirements, reliability testing included wire pull testing, ball bond shear testing, solder ball shear testing and cold ball pull testing. Investigated surface finishes: ENEPIG, ENIG, electrolytic NiAu, SOP, electroless palladium, immersion tin, immersion silver, direct gold.
Download complete paper here: pdf file (File size 910 kB)
Properties of High P ENIG Process on Flexible Boards
Kuldip Johal, Hugh Roberts, Atotech USA, Inc, Sven Lamprecht, Christian Wunderlich, Guenter Heinz, Atotech Deutschland, April 2005
In this technical paper the reliability of ENIG with a high-phosphorous electroless nickel layer is compared to a medium-phosphorous electroless nickel deposit. It is looked at the mechanical strength of the solder joints at one hand by means of ball shear test and at the other hand at bending capabilities by using results of bending tests, hardness measurements and SEMs.
In particular Young's Modulus (stress-to-strain ratio) is evaluated to show a direct relationship between the phosphorus content of the electroless nickel deposit and the ductility of the overall ENIG finish. Electroless nickel deposits of varying phosphorous content and thickness were applied.
Download complete paper here: pdf file (File size 410 kB)