printed circuit board

Topics: Young's modulus, Finite element method, Materials science Pages: 6 (3161 words) Published: June 24, 2014
Thermoelastic Properties of Printed Circuit Boards: Effect of Copper Trace
Hu Guojun, Goh Kim Yong, Luan Jing-en, Lim Wee Chin and Xavier Baraton STMicroelectronics, 629 Lorong 4/6 Toa Payoh, Singapore 319521, Singapore Tel: +65 63897056. E-mail address: guojun.hu@st.com

Abstract
After encapsulation, thermo-mechanical deformation builds up within the electronic packages due to coefficient of thermal expansion (CTE) mismatch between the respective materials within the package as it cools to room temperature. Printed circuit boards (PCB) are designed and manufactured with a variety of polyamide materials such as solder mask, metallic material such as copper trace, composite materials such as prepreg and core material. Polyamide materials such as solder mask and composite materials such as prepreg play important factor on the total deformation of laminate package due to the large CTE. On the other hand, the patterning of the copper layers also exerts important influence to the thermal mechanical behavior of the substrate due to the consistent large Young’s modulus of copper at both room temperature and reflow temperature compared with the small Young’s modulus of polyamide materials. Some approximate methods based on rule of mixtures have been used for estimating material properties in layers of copper mixed with interlayer dielectric material. However, few techniques include the effect of copper trace pattern and copper percentage. The detailed comparison of different approximate methods has been done in this paper and a new methodology has been developed to include the effect of Poisson’s ratio, copper trace pattern and copper percentage. The equivalent properties of copper trace layer using the new methodology have been compared with the results using the detailed finite element simulation of the actual laminate substrates. The results show that the contribution of the copper trace on in-substrate-plane modulus becomes more and more important with the increase of copper percentage.

Key words: PCB, substrate, copper trace, FEA, Young’s modulus, CTE 1. Introduction
Warpage of IC packages after encapsulation
is a major concern in package development because
of the risk of die cracking if a tensile stress is built
up in the die particularly in thin packages [1]. Also
excess warpage can cause problems with mounting
the package onto a PCB or another package such as
package-on-package (PoP). Realistic modeling and
analysis of the mechanical performance and
reliability of electronic packages requires
sophisticated constitutive models for the many
complex, non-traditional engineering materials that
compose these intricate devices. The proper
modeling of the behavior of such plastic materials is
becoming important in the reliability studies of these
IC packages.
One challenge is the proper simulation of the
thermal mechanical properties of the copper trace
layer which consist of metallic material and
dielectric material. The dielectric material such as
solder mask and prepreg play important factor on the
total deformation of laminate package due to the
large CTE (see Table 1). On the other hand, the
metallic material such as the copper trace exerts
important influence to the thermal mechanical
behavior of the substrate due to its consistent large

Young’s modulus from room temperature to solder
reflow temperature. There are a few studies on the
approximation and computation methods of
equivalent laminate properties, but few techniques
include the effect of Poisson’s ratio, copper trace
pattern and copper percentage. The effective thermomechanical properties of the trace layer are dependent upon copper trace pattern, copper
percentage and properties of the constituent
materials. Some study uses one direction orthogonal
copper layout to equivalence the nearly symmetrical
copper trace pattern [2] which may overestimate the
orientation effect of copper trace pattern. On the
other hand, some...


References: Manufacturing Conference, Malaysia, pp. 1–7,
2008.
Reliability, Vol. 42, No. 6, pp. 943-949, 2002.
Conference (ECTC), Florida, USA, pp. 1582 –
1586, 2008.
York, 2006.
Pennsylvania, 1980.
USA, pp. 503–510, 1998.
Packaging, Vol. 131, No. 1, 011010 (6 pages),
2009.
Continue Reading

Please join StudyMode to read the full document

You May Also Find These Documents Helpful

  • Essay on home made circuit board
  • Circuit Board Case Study Research Paper
  • Circuit Board Fabricators, Inc. Case Analysis – Week 3 Essay
  • Circuit Board Corporation Essay
  • Essay on Printed Crt
  • Integrated Circuits Technology Research Paper
  • Business Report on Electronic Circuit Board Plc Essay
  • Thesis Advance Logic Circuits Essay

Become a StudyMode Member

Sign Up - It's Free