News

Ball Bumping

“Gold Bump Technologies: A Comparison of Serial Processing (Ball Bumping) and Batch Processing (Plating)”

Authors: Daniel Evans, Jr. and Mark S. Greenwell.

Abstract: Ball bumping can provide advantages over plated-up bumps for several reasons: ball bumps can be more cost effective; they can support multiple substrate attach technologies; single pass ball bump shapes are available without the planarization requirement; and ball bumping offers a technique for manufacturing unique thin flat pancake shaped bumps and other shapes. One novel flat shaped ball bump reviewed is created in a single pass without the need for secondary coining operations, thus reducing the handling and impact on the die pad. Ball bumps 68 µm diameter by 12 µm height are produced for limited applications. Many variations in shapes of ball bumps including the unique flat bump come from the same machine tooling. Each different shape has a best-fit application. For wafers with greater than 150,000 bump count and many wafers to bump, plating is likely the answer. (SMTAI, September 2005)

Components

“Powerchip: Integrated Power For Wireless Microsystems”

Authors: Jenniffer DeGreeff, Patrick Fleig and Charles Lakeman; jdegreeff@tplinc.com.

Abstract: By combining energy generation and energy storage, the PowerChip is a solution for power in inaccessible or remote microsystems. The energy generation units can convert ambient energy into electrical energy using proprietary conditioning circuitry and store it in a volumetric microbattery or micro-supercapacitor. Microsupercapacitors have a high power density and can withstand thousands of cycles. Micro-batteries can be used as a backup energy source in the absence of ambient energy. The control circuitry ensures efficient use of harvested energy and maintains the charge profiles required for batteries and supercapacitors while using a minimum amount of power. This paper also demonstrates the feasibility of a solar and a vibrational energy harvesting. (SMTAI, September 2005)

Dispensing

“Reducing Hand Fatigue and Variability in Benchtop Assembly Processes”

Author: EFD Inc., efd-inc.com/whitepapers/index.html

Abstract: Common problems with manual fluid application tools include hand fatigue related to repetitive motion and safety issues stemming from potential exposure to hazardous fumes and skin irritants. Also, manual systems are operator-dependent and thus prone to variation. Air-powered dispensers can reduce or resolve these problems.

Printing

“Study of Noise Factors in Solder Paste Printing”

Author: Aleksandra Djordjevic; aleksandra.djordjevic@delphi.com.

Abstract: The goal of this study was to optimize a typical printing process by adjusting parameters from the machine selection menu, and to study underlying noise factors and quantify their impacts on the process output. A Six Sigma structured approach was used to identify the greatest sources of variation of the solder paste printing process. (SMTAI, September 2005)

Surface Finishes

“Reliability of Tin Terminated Components in a Lead-Free System”

Authors: Jorge A. Manriquez, Ph.D., Oscar Molina, Juan C. Cardenas and Brian J. Toleno, Ph.D.; jmanriquez@itesm.mx.

Abstract: This experimental study evaluated the effects on solder joint reliability using Pb-free solders and Sn-finished components on boards with Pb-base metalizations. Variables in the study were solder chemistry (Sn63Pb37, Sn95.5Ag3.8Cu0.7, Sn96.3Ag2.5Cu0.7Sb0.5) and thickness of nickel barrier (50 µin, 30 µin) below the tin finish of 0603 BaTiO3 ceramic capacitors. Test vehicles were HASL-SnPb10 finished. SMT boards were assembled with printing parameters and reflow profiles optimized for each condition. Fillet formation was inspected according to J-STD-001B. The first portion of the study is an isothermal test at 125°C and 25V DC (MIL-STD-202G) to evaluate formations of CuSn and NiSn intermetallic compounds at solder-metal interfaces. Twenty-four boards with 20 capacitors each were evaluated. IMC thickness measurements were taken from samples after 0, 65, 130 and 264 hrs., using a SEM/EDX unit. Capacitance measurements were taken at the start and the end of the isothermal aging test. The second portion of the study used a thermal cycling stress condition (IPC-SM-785) using a +25/+100/+25°C cycle with 15 min. dwell time at each temperature extreme and a 15°C/min. heating/cooling step. Forty-two boards with 20 capacitors each were evaluated according to failing criteria by loss of electrical continuity and by maximum variation of capacitance. Growth of Cu3Sn and Ni3Sn IMCs along the solder-metal interfaces was very similar for all types of solder chemistries. All tested conditions produced assemblies that complied with expected reliability. Two capacitors presented a higher than 25% reduction in capacitance before 1000 hrs., both from the antimony containing Pb-free solder joints when capacitors had a 30 µin Ni barrier. The paper discusses results and proposes possible relationships between joint-level reliability and studied variables. (SMTAI, September 2005)

Circuits Assembly provides abstracts of papers from recent industry conferences and company white papers. With the amount of information increasing, our goal is to provide an added opportunity for readers to keep abreast of technology and business trends.