Examination of Solder Interconnects Formed on ENEPIG Finished Printed Wiring Boards Under Drop Loading Conditions

2013 ◽  
Author(s):  
Adam Pearl ◽  
Michael Osterman
Keyword(s):  
Failure Mode ◽  
Surface Finish ◽  
Electroless Nickel ◽  
Primary Role ◽  
Mechanical Shock ◽  
Printed Wiring Boards ◽  
Printed Wiring Board ◽  
Bga Packages ◽  
Immersion Silver ◽  
Component Interface

Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG), which has been used in component packaging, has been gaining attention as a surface finish for printed wiring boards. The primary role of a printed wiring board surface finish is to provide a solderable surface for assembly, creating a reliable solder interconnect. With regards to reliability, the increased use of mobile electronics has resulted in the need to consider the ability of interconnects to withstand repeated mechanical shocks. This paper examines the drop reliability of both SnPb and SAC305 interconnects formed on ENEPIG finished printed wiring boards. For comparison, the drop reliability test results for similar boards with Immersion Silver (ImAg) board finish are included. Test boards include BGA and resistor packages. The boards are dropped 500 times to achieve failure across the components. Failure analysis revealed that the dominant failure mode for BGA packages on the ENEPIG finish was cracking in the solder balls at the component interface, while for the ImAg finish the dominant failure mode was cratering in the board laminate below the solder pad. For the resistor packages, cracking through the solder joint at the component interface was the dominant failure mode for both the ENEPIG and ImAg finishes. The drop results indicate that both finishes are suitable for systems that could experience mechanical shock due to drop, with components soldered onto ENEPIG with a SAC 305 solder having the highest survivability. The combination of SnPb and ImAg was found to be superior to SAC 305 and ImAg.

Mechanical and Thermal Board Level Reliability Comparison Between Electroless Ni Im. Au and Solder on Pad Surface Finishes for Large Flip Chip BGA Packages

2006 ◽  
Author(s):  
Gnyaneshwar Ramakrishna ◽  
Donghyun Kim ◽  
Mudasir Ahamad ◽  
Lavanya Gopalakrishnan ◽  
Mason Hu ◽  
...  
Keyword(s):  
Surface Finish ◽  
Flip Chip ◽  
High Reliability ◽  
Electroless Nickel ◽  
Temperature Cycling ◽  
Design Parameters ◽  
Temperature Cycle ◽  
Bga Packages ◽  
Reliability And Robustness ◽  
Board Level

Large Flip Chip BGA (FCBGA) packages are needed in high pin out applications (>1800), e.g., ASIC's and are typically used in high reliability and robustness applications. Hence understanding the package reliability and robustness becomes one of paramount importance for efficient product design. There are various aspects to the package that need to be understood, to ensure an effective design. The focus of this paper is to understand the BGA reliability of the package with particular reference to comparison of the surface finish, vis-a`-vis, between Electroless Nickel Immersion Gold (ENIG) and Solder On Pad (SOP) on the substrate side of the package, which are the typical solutions for large plastic FC-BGA packages. Tests, which include board level temperature cycling, monotonic bend and shock testing have been conducted to compare the two surface finish options. The results of these tests demonstrate that the mechanical strength of the interface exceeds by a factor of two for the SOP surface finish, while BGA design parameters play a key role in ensuring comparative temperature cycle reliability in comparison with ENIG packages.

Reliability Analysis of Lead-Free Solder Joints with Solder Doping on Harsh Environment

2016 ◽  
Vol 2016 (1) ◽  
pp. 000117-000122 ◽  
Author(s):  
Cong Zhao ◽  
Thomas Sanders ◽  
Zhou Hai ◽  
Chaobo Shen ◽  
John L. Evans
Keyword(s):  
Surface Finish ◽  
Isothermal Aging ◽  
Electroless Nickel ◽  
Lead Free ◽  
Lead Free Solder ◽  
Solder Paste ◽  
Surface Mount ◽  
Surface Finishes ◽  
Free Solder ◽  
Immersion Silver

Abstract This paper investigates the effect of long term isothermal aging and thermal cycling on the reliability of lead-free solder mixes with different solder compositions, PCB surface finishes, and isothermal aging conditions. A variety of surface mount components are considered, including ball grid arrays (BGAs), quad flat no-lead packages (QFNs) and 2512 Surface Mount Resistors (SMRs). 12 lead-free solder pastes are tested; for BGA packages these are reflowed with lead-free solder spheres of SAC105, SAC305 and matched doped solder spheres (“matched” solder paste and sphere composition). Three surface finishes are tested: Organic Solderability Preservative (OSP), Immersion Silver (ImAg), and Electroless Nickel Immersion Gold (ENIG). All test components are subjected to isothermal aging at 125°C for 0 or 12 months, followed by accelerated thermal cycle testing from −40°C to 125°C. Data from the first 1500 cycles is presented here, with a focus on the effect of surface finish on package reliability. Current results demonstrate that the choice of surface finish has a strong effect on reliability. However, different solder materials appear to show different reliability trends with respect to the surface finishes, and the reliability trends of BGA and SMR packages also diverge.

Effect of ENEPIG Surface Finish on the Vibration Reliability of Solder Interconnects

2013 ◽  
Vol 2013 (1) ◽  
pp. 000115-000119 ◽  
Author(s):  
Sandeep Menon ◽  
Adam Pearl ◽  
Michael Osterman ◽  
Michael Pecht
Keyword(s):  
Electroless Nickel ◽  
Copper Metallization ◽  
Printed Wiring Boards ◽  
Solder Interconnects ◽  
Solder Interconnect ◽  
Failure Data ◽  
Surface Finishes ◽  
Interconnect Reliability ◽  
Immersion Silver ◽  
The Impact

Surface finishes are used to preserve and promote solderability of exposed copper metallization on printed wiring boards. While in the best of worlds, the solder used in assembly should dictate the solder interconnect reliability, surface finishes are known to have an effect. The effect of surface finishes on solder interconnect reliability can be particularly strong under high strain rate loading conditions. In this study, durability of solder interconnects formed between BGAs and electroless nickel, electroless palladium, immersion gold (ENEPIG) finished pads assembled using SnPb and SAC305 solders under harmonic vibration loading is examined. ENEPIG test specimens with two thicknesses of palladium were evaluated. Isothermal preconditioning levels at 100°C for 24 hrs and 500 hrs were included to evaluate the impact of intermetalic evolution on the durability of the soldered interconnects. For comparison, tests specimens created with immersion silver (ImAg) finished printed wiring boards were also included. The failure data obtained found the durability of interconnects formed with ENEPIG finish was comparable or better durability than the durability of interconnects formed with ImAg finish irrespective of the solder. The tests indicate that the use of a thicker palladium layer reduced the degradation in durability which occurred from isothermal aging.

The Effect of Bismuth on Intermetallics Growth between Lead-Free Solders and Electroless Nickel Immersion Silver (ENIMAG) Surface Finish

2019 ◽  
Vol 796 ◽  
pp. 183-188
Author(s):  
Jaidi Zolhafizi ◽  
Osman Saliza Azlina
Keyword(s):  
Grain Size ◽  
Intermetallic Compound ◽  
Surface Finish ◽  
Aging Treatment ◽  
Electroless Nickel ◽  
Optical Microscope ◽  
Circuit Board ◽  
Lead Free ◽  
Reflow Soldering ◽  
Immersion Silver

Surface finish is coating layer plated on a bare copper board of printed circuit board (PCB). Among PCB surface finishes, Electroless Nickel/Immersion Gold (ENIG) finish is a top choice among electronic packaging manufacturer due to its excellent properties for PCB. However, the use of gold element in ENIG is very high cost and the black pad issue have not been resolved. Thus, by introducing an Electroless Nickel/Immersion Silver (ENImAg) as alternative surface finish hopefully can reduce the cost and offer better properties. The aim of this study is to investigate the effect of bismuth on interfacial reaction during reflow soldering between Sn-2.5Ag (SA25), Sn-3.4Ag-4.8Bi (SAB3448) and ENIMAG surface finish. Solder balls with sizes of 500μm diameters were used. The characteristics of intermetallic compound (IMC) were analyzed by using scanning electron microscopy (SEM), optical microscope and energy dispersive x-ray (EDX). After reflow soldering, the result revealed that only the irregular circle-shape of (Cu,Ni)6Sn5IMC layer was formed at the interface and change to an irregular rod-like shape meanwhile the irregular needle-shape (Ni,Cu)3Sn4was appeared after aging treatment. The result also indicated that, the grain size and thickness of IMC for SAB3448 is smaller and thinner compared to the SA25. The IMC thickness is proportional to the aging duration and IMC morphology for both solder are became thicker, larger and coarser after isothermal aging. No bismuth particle has been detected on SAB3448 solder during top surface examination. In addition, the Bi has been observed can reduce the grain size and the growth rate of IMC. Keywords: ENIMAG, reflow soldering, lead-free solder, intermetallic compound, bismuth

Case Studies of Brittle Interfacial Failures in Area Array Solder Interconnects

2000 ◽  
Author(s):  
George M. Wenger ◽  
Richard J. Coyle ◽  
Patrick P. Solan ◽  
John K. Dorey ◽  
Courtney V. Dodd ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Case Studies ◽  
Failure Modes ◽  
Electroless Nickel ◽  
Electrical Performance ◽  
Printed Wiring Board ◽  
Solder Interconnects ◽  
Area Array ◽  
Surface Finishes ◽  
Soldering Reaction

Abstract A common pad finish on area array (BGA or CSP) packages and printed wiring board (PWB) substrates is Ni/Au, using either electrolytic or electroless deposition processes. Although both Ni/Au processes provide flat, solderable surface finishes, there are an increasing number of applications of the electroless nickel/immersion gold (ENi/IAu) surface finish in response to requirements for increased density and electrical performance. This increasing usage continues despite mounting evidence that Ni/Au causes or contributes to catastrophic, brittle, interfacial solder joint fractures. These brittle, interfacial fractures occur early in service or can be generated under a variety of laboratory testing conditions including thermal cycling (premature failures), isothermal aging (high temperature storage), and mechanical testing. There are major initiatives by electronics industry consortia as well as research by individual companies to eliminate these fracture phenomena. Despite these efforts, interfacial fractures associated with Ni/Au surface finishes continue to be reported and specific failure mechanisms and root cause of these failures remains under investigation. Failure analysis techniques and methodologies are crucial to advancing the understanding of these phenomena. In this study, the scope of the fracture problem is illustrated using three failure analysis case studies of brittle interfacial fractures in area array solder interconnects. Two distinct failure modes are associated with Ni/Au surface finishes. In both modes, the fracture surfaces appear to be relatively flat with little evidence of plastic deformation. Detailed metallography, scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), and an understanding of the metallurgy of the soldering reaction are required to avoid misinterpreting the failure modes.

Advances in Fine Pitch Off-Chip Interconnections Through the Use of a Novel Surface Finish

2015 ◽  
Vol 2015 (DPC) ◽  
pp. 001531-001563
Author(s):  
Arnd Kilian ◽  
Gustavo Ramos ◽  
Rick Nichols ◽  
Robin Taylor ◽  
Vanessa Smet ◽  
...  
Keyword(s):  
Low Temperature ◽  
Surface Finish ◽  
System Integration ◽  
High Performance ◽  
Semiconductor Industry ◽  
Electroless Nickel ◽  
Interfacial Stress ◽  
Copper Oxidation ◽  
Fine Pitch ◽  
Metallurgical Bond

One constant in electronic system integration is the continuous trend towards smaller devices with increased functionality, driven by emerging mobile and high-performance applications. This brings the need for higher bandwidth at lower power, translating into increased I/O density, to enable highly-integrated systems with form factor reduction. These requirements result in the necessity of interconnection pitch-scaling, below 30 μm in the near future, and substrates with high wiring densities, leading to routing with sub 5 μm L/S where standard surface finishes (ENIG, ENEPIG) are no longer applicable. Copper pillar with solder caps technology is currently the prevalent solution for off-chip interconnections at fine pitch, dominating the high performance and mobile market with pitches as low as 40 μm in production. However, this technology faces many fundamental limitations in pitch scaling below 30 μm, due to solder bridging, IMC-solder interfacial stress management, and poor power handling capability of solders. All-copper interconnections without solder are very sought after by the semiconductor industry and have been applied to 3D-IC stacking, however no cost effective, manufacturable and scalable solution has been proposed to date for HVM and application to non CTE matched package structures. The low temperature Cu-Cu interconnection technology without solder recently patented by Georgia Tech PRC is one of the most promising solutions to this problem. The main bottleneck of copper oxidation is dealt with by application of ENIG on the Cu bumps and pads, enabling formation of a reliable metallurgical bond by thermocompression bonding (TCB) at temperatures below 200°C, in air, with cycle-times compatible with HVM targets. However, to ensure a bump collapse of 3 μm to overcome non-coplanarities and warpage, a pressure of 300MPa is used in the Process-of-Record (PoR) conditions, limiting the scalability of this technology. This paper introduces a novel Electroless Palladium / Autocatalytic Gold (EPAG) surface finish process, to enable the next generation of high density substrates and interconnections. With circa 100nm-thin Pd and Au layers, the EPAG finish can be applied to fine L/S wiring, with no risk of bridging adjacent Cu traces, even with spacing below 5 μm. Further, the EPAG finish is compatible with current interconnection processes; such as wire bonding, and the Cu pillar and solder cap technology for fine-pitch applications. For further pitch reduction, the EPAG surface finish was coupled to GT PRC's low-temperature Cu-interconnections, in an effort to reduce the bonding load for enhanced manufacturability without degrading the metallurgical bond or reliability. This paper is the first demonstration of such interconnections. The effect of the surface finish thickness and composition on the bonding load, assembly yield, quality of the metallurgical bond was extensively evaluated based on analysis of the metal interface microstructures and the chemical composition of the joints. The current PoR using Electroless Nickel / Immersion Gold (ENIG) coated Cu pillars and pads was used as reference. A novel surface finish is introduced, which allows formation of Cu-Cu interconnections without solder at lower pressure, between a silicon die and glass, organic or silicon substrate at fine pitch, allowing the performance improvements demanded by the IC Packaging Industry.

Electroplating and Electroless Plating Process Development for DuPont™ GreenTape™ 9K7 LTCC

2013 ◽  
Vol 2013 (CICMT) ◽  
pp. 000283-000287
Author(s):  
Allan Beikmohamadi ◽  
Steve Stewart ◽  
Jim Parisi ◽  
Mark McCombs ◽  
Michael Smith ◽  
...  
Keyword(s):  
Thick Film ◽  
Surface Finish ◽  
Electroless Plating ◽  
Process Development ◽  
Cost Effective ◽  
Electroless Nickel ◽  
Free Atmosphere ◽  
Gold Plating ◽  
Cost Effective Approach ◽  
Easy Integration

Low Temperature Co-fired Ceramic (LTCC) technology provides an attractive packaging platform for microwave and millimeter wave circuits and systems due to its unique properties. Generally, thick film gold or silver conductors are used as metallizations on LTCC substrates along with occasional use of copper thick films. This paper reports methods and results of extensive process development experiments DuPont Microcircuit Materials has undertaken to establish a commercially viable plating process for the market leading DuPont™ GreenTape™ 9K7 LTCC system. Both Electroplating and Electroless plating processes are investigated in this work. These techniques provide certain advantages when used in isolation or in combination with standard thick film metallizations, helping to extend their applicability. Electroplating of copper on LTCC provides a means of using copper as the external conductor without having to use complicated firing processes in oxygen-free atmosphere as required for copper thick film. This approach leads to a much more cost effective approach if copper is required as the external metal. Electroless Nickel/Gold plating (ENIG) of both silver and copper (electroplated and/or thick film) provides an industry standard, highly reliable, robust surface finish. Such surface finish enables easy integration of both soldering and wire bonding processes.

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