Electronics Manufacturing Technical Articles

Ready to Start Measuring PCB Warpage during Reflow? Why and How to Use the New IPC-9641 Standard

Aug 19, 2014 | Ken Chiavone

Understanding warpage of package attach locations on PCBs under reflow temperature conditions is critical in surface mount technology. A new industry standard, IPC 9641, addresses this topic directly for the first time as an international standard.

This paper begins by summarizing the sections of the IPC 9641 standard, including, measurement equipment selection, test setup and methodology, and accuracy verification. The paper goes further to discuss practical implementation of the IPC 9641 standards. Key advantages and disadvantages between available warpage measurement methods are highlighted. Choosing the correct measurement technique depends on requirements for warpage resolution, data density, measurement volume, and data correlation. From industry experience, best practice recommendations are made on warpage management of PCB land areas, covering how to setup, run, analyze, and report on local area PCB warpage.

The release of IPC 9641 shows that flatness over temperature of the package land area on the PCB is critical to the SMT industry. Furthermore, compatibility of shapes between attaching surfaces in SMT, like a package and PCB, will be critical to product yield and quality in years to come....

Publisher: Akrometrix

Advanced Organic Substrate Technologies To Enable Extreme Electronics Miniaturization.

Aug 14, 2014 | Susan Bagen, Dave Alcoe, Kim Blackwell, Frank Egitto.

High reliability applications for high performance computing, military, medical and industrial applications are driving electronics packaging advancements toward increased functionality with decreasing degrees of size, weight and power (SWaP) The substrate technology selected for the electronics package is a key enabling technology towards achieving SWaP. Standard printed circuit boards (PWBs) utilize dielectric materials containing glass cloth, which can limit circuit density and performance, as well as inhibit the ability to achieve reliable assemblies with bare semiconductor die components. Ceramic substrates often used in lieu of PWBs for chip packaging have disadvantages of weight, marginal electrical performance and reliability as compared to organic technologies. Alternative materials including thin, particle-containing organic substrates, liquid crystal polymer (LCP) and microflex enable SWaP, while overcoming the limitations of PWBs and ceramic.

This paper will discuss the use of these alternative organic substrate materials to achieve extreme electronics miniaturization with outstanding electrical performance and high reliability. The effect of substrate type on chip-package interaction and resulting reliability will be discussed. Microflex assemblies to achieve extreme miniaturization and atypical form factors driven by implantable and in vivo medical applications are also shown....

Publisher: i3 Electronics

Gold Embrittlement In Lead-Free Solder.

Aug 07, 2014 | Craig Hillman, Nathan Blattau, Joelle Arnold, Thomas Johnston, Stephanie Gulbrandsen; DfR Solutions, Julie Silk, Alex Chiu; Agilent Technologies.

Gold embrittlement in SnPb solder is a well-known failure mechanism in electronic assembly. To avoid this issue, prior studies have indicated a maximum gold content of three weight percent. This study attempts to provide similar guidance for Pb-free (SAC305) solder. Standard surface mount devices were assembled with SnPb and SAC305 solder onto printed boards with various thicknesses of gold plating. The gold plating included electroless nickel immersion gold (ENIG) and electrolytic gold of 15, 25, 35, and 50 microinches over nickel. These gold thicknesses resulted in weight percentages between 0.4 to 7.0 weight percent....

Publisher: DfR Solutions (acquired by ANSYS Inc)

Electrostatic Theory of Metal Whiskers.

Jul 31, 2014 | V. G. Karpov, Department of Physics and Astronomy, University of Toledo.

Metal whiskers often grow across leads of electric equipment and electronic package causing current leakage or short circuits and raising significant reliability issues. The nature of metal whiskers remains a mystery after several decades of research. Here, the existence of metal whiskers is attributed to the energy gain due to electrostatic polarization of metal filaments in the electric field. The field is induced by surface imperfections: contaminations, oxide states, grain boundaries, etc. A proposed theory provides closed form expressions and quantitative estimates for the whisker nucleation and growth rates, explains the range of whisker parameters and effects of external biasing, and predicts statistical distribution of their lengths....

Publisher: University of Toledo

Copper Wire Bond Failure Mechanisms.

Jul 24, 2014 | Randy Schueller, Ph.D.

Wire bonding a die to a package has traditionally been performed using either aluminum or gold wire. Gold wire provides the ability to use a ball and stitch process. This technique provides more control over loop height and bond placement. The drawback has been the increasing cost of the gold wire. Lower cost Al wire has been used for wedge-wedge bonds but these are not as versatile for complex package assembly. The use of copper wire for ball-stitch bonding has been proposed and recently implemented in high volume to solve the cost issues with gold. As one would expect, bonding with copper is not as forgiving as with gold mainly due to oxide growth and hardness differences.

This paper will examine the common failure mechanisms that one might experience when implementing this new technology....

Publisher: DfR Solutions (acquired by ANSYS Inc)

Enhancing Thermal Performance in Embedded Computing for Ruggedized Military and Avionics Applications.

Jul 17, 2014 | Darren Campo, Jens Weyant, Bryan Muzyka

Embedded computing systems used in many military and avionics applications are trending toward higher heat fluxes, and as a result performance is being hindered by thermal limitations. This is intensified by the high ambient conditions experience by today’s modern warfighter. In many applications liquid cooling is replacing air flow through chassis for both thermal and environmental benefits(...)

This paper outlines a series of passive thermal improvements which are easily integrated into legacy, or existing, systems and can provide a 3-4x increase in dissipated power....

Publisher: Advanced Cooling Technologies

Fatigue Damage Behavior of a Surface-mount Electronic Package Under Different Cyclic Applied Loads.

Jul 10, 2014 | Ren Huai-Hui, Wang Xi-Shu

This paper studies and compares the effects of pull–pull and 3-point bending cyclic loadings on the mechanical fatigue damage behaviors of a solder joint in a surface-mount electronic package.

The comparisons are based on experimental investigations using scanning electron microscopy (SEM) in-situ technology and nonlinear finite element modeling, respectively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure....

Publisher: Tsinghua University

Effect of Cu–Sn intermetallic Compound Reactions on the Kirkendall Void Growth Characteristics in Cu/Sn/Cu Microbumps

Jul 02, 2014 | Jong-Myeong Park, Seung-Hyun Kim, Young-Bae Park - Andong National University, Myeong-Hyeok Jeong - NEPES Corporation.

Growth behaviors of intermetallic compounds (IMCs) and Kirkendall voids in Cu/Sn/Cu microbump were systematically investigated by an in-situ scanning electron microscope observation. Cu–Sn IMC total thickness increased linearly with the square root of the annealing time for 600 h at 150°C, which could be separated as first and second IMC growth steps. Our results showed that the growth behavior of the first void matched the growth behavior of second Cu6Sn5, and that the growth behavior of the second void matched that of the second Cu3Sn. It could be confirmed that double-layer Kirkendall voids growth kinetics were closely related to the Cu–Sn IMC growth mechanism in the Cu/Sn/Cu microbump, which could seriously deteriorate the mechanical and electrical reliabilities of the fine-pitch microbump systems...

Publisher: Nepes Corporation

Enhancing Mechanical Shock Performance Using Edgebond Technology

Jun 26, 2014 | Steven Perng, Tae-Kyu Lee, and Cherif Guirguis - Cisco Systems, Inc., Edward S. Ibe - Zymet, Inc.

Edgebond adhesives have been widely used by the industry for improving the shock performance of area array packages. Most of the studies focus on the impact of material properties, such as coefficient of thermal expansion (CTE) and glass transition temperature (Tg), on reliability at room temperature. However, the operating temperature of a component on the printed circuit board bonded with edgebond adhesive can be close to or exceed Tg of the adhesive, where the material properties may be very different than at room temperature....

Publisher: Cisco Systems, Inc.

OOOH Colors, It Must Be Lead Free

Jun 23, 2014 | John Maxwell, Director of Product Development, Johanson Dielectrics Inc.

It was unusual to see chip terminations change colors when tin lead solders were used but with the introduction of lead free reflow soldering and the corresponding increases in reflow temperatures terminations are now changing colors. Two conditions are present when reflow temperatures are increased for lead free solder alloys that leads to discoloration. Reflow temperatures are above the melting point of tin (Sn MP is 232oC). Air temperatures commonly used in forced convection reflow systems are high enough to both melt the tin plating on the termination allowing it to be pulled into the solder joint due to solder joint liquid solder surface tension leaving behind the exposed nickel barrier. Now those metal oxide colors will be visible due to high air temperatures during reflow....

Publisher: Johanson Dielectrics, Inc.