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Measurement and Modeling of In Situ Lead Stiffness of Surface Mounted Packages
Abstract
An approach to the experimental determination of in situ lead
stiffness has been used to measure selected surface mount component
(SMC) lead stiffness under simulated service conditions. Good agreement
was obtained between the experimental data and three-dimensional elastic
beam finite element analysis (FEA). The agreement was achieved through
the use of a stiffness matching point, which provided insight into the
level of constraint provided by the solder joint at the lead foot. When
adequate solder was available, the solder served as a built-in boundary.
When there was insufficient solder creep relaxation in the solder
because of the high level of stress in the joint permitted rotation of
the lead and the solder served as a pinned joint. Location of the
stiffness matching point was found to be approximately 0.08 mm (0.003
in) below the solder fillet on the lead for the lateral stiffness
component and about 0.15 mm (0.006 in) above the land for the transverse
stiffness component
... Stiffness measurement of tissues using dedicated probes and ultrasonic transducers is discussed in [2]. In [3], stiffness measurement in surface mount package is calculated by causing deformation and measuring it. Stiffness measurement using ultrasonic technique is discussed in [4]. ...
In this paper, we propose a scheme to measure the Elasticity Modulus of textile using image processing techniques, here the elasticity modulus is measured indirectly by measuring stiffness of the material. The material whose stiffness is to be measured is subjected to a known force, and the deformation caused in the material due to applied load is measured using image processing. The deformation caused depends on stiffness of the textile used, by making use of relation between stiffness and deformation we can calculate the stiffness. Using this stiffness, elasticity modulus is derived. Web camera is used for the purpose of capturing the image, which is then acquired on the LabVIEW platform for processing. The data is processed by image processing techniques to compute stiffness and elasticity. The system was subjected to test and results showed it had achieved desired objectives.
Reliability is the characteristic of an object that provides a required function whenever such a function is sought. Failure to provide the function is a lack of reliability. Today’s consumer of electronic goods expects to see a news report when he or she turns the TV power on; but it is not a tragedy if the television is unreliable. However, the electronic data-processing user has become much more dependent on the reliability of a system. Air-traffic control systems, medical diagnostic systems, factory production systems, and environmental control systems for high risk chemical industries are examples of some areas where system reliability is a must, and failure may be life threatening.
Solder Joints used in surface mount technology experience thermomechanical fatigue due to the mismatches in coefficients of thermal expansion of the electrical component, the printed circuit board, and the solder itself, which during thermal cycles causes the solder Joint to undergo shear strains. The purpose of this study was to examine and explain the thermomechanical fatigue damage mechanisms of various types of solder compositions. Shear, creep, low cycle fatigue, and thermomechanical fatigue tests were conducted in this research. The development of cracks through heterogeneously coarsened, Sn-enriched bands was observed in Sn-Pb eutectic and solid solution strengthened alloys failed in thermomechanical fatigue. The dominant damage mechanism for these alloys was determined to be dislocation climb. Dispersion strengthening inhibited heterogeneous coarsening, and resulted in solders with greater thermomechanical fatigue lifetimes.
The high temperature steady state deformation behaviour of PbSn eutectic alloy was investigated over wide ranges of grain size (9.7 – 32.0 μm), temperature (298 – 443 K) and strain rate (10−7 – 10−2 s−1), after stability of microstructure and strength had been achieved through prior tensile deformation. The σ-ϵ plots for these materials consisted of regions II and III. In region II the strain rate sensitivity index m is 0.6 ± 0.1 and the grain size exponent p is 3.34 ± 0.23. The activation energy Q in region II was found to depend on temperature with Q = 44.7 ± 1.1 kJ mol−1 below about 408 K and Q = 81.1 ± 3.9 kJ mol−1 above this temperature. These experimental parameters do not agree with any of the superplasticity models that have been proposed to date. However, in region III the parameters m = 0.09 ± 0.01, p = 1.00 ± 0.72 and Q = 100.0 ± 8.8 kJ mol−1 observed are in better agreement with the recovery creep model of Gifkins.
Equations for the directional spring constants for common compliant lead designs for surface-mounted (SM) components are given. The lead configurations include the straight J-lead, dimpled J-lead, gull-wing lead, butt-lead (I-lead), and S-bend lead. The updated lead geometries and analysis method represent an expanded treatment of previous lead compliance studies by the author. The present objectives are to demonstrate applications of the analytic tool developed and identify the directional stiffness parameters that should be considered when assessing the compliance of a specific lead design. Comparative lead compliance evaluation has been performed for different SM components tested using accelerated function cycling or circuit-board dynamic bending. The solder-joint cycles-to-failure data indicate that significant differences in attachment fatigue performance can be correlated with disparate lead compliance among the SM packages tested
A 12×12 stiffness matrix of the gull-wing lead and solder
joint in a plastic quad flat pack (PQFP) surface-mount assembly was
obtained by using a three-dimensional finite-element method. Deformation
of the composite structure for each imposed unit displacement (or
rotation) then obtained. The whole-field stress distributions in the
gull-wing and solder joint provide a better understanding of their
characteristics. The results presented herein can provide guidelines for
the design of PQFP gull-wing leads and solder-joint reliability
The objective of this work is to analyze stresses induced in the
solder joint and to minimize the risk of crack initiation at the
solder-joint level. Thermomechanical analysis of solder joints and
thermomechanical simulation have helped the authors to optimize the
process, to give recommendations for solder-joint inspection, and to put
in place new quality insurance procedures that take into account the
thermomechanical parameters of components and mounting processes.
Experimental results support these first simulation results.
Recommendations and proposals for new quality insurance procedures are
presented
A simplified analytical model of hybrid-integrated-circuit
(HIC)/printed-wire-board (PWB) assembly bowing is developed to explain a
paradoxical situation, observed by T. F. Marinis, R. C. Reinert and W.
M. Sherry (Proc. 34th Electronic Components Conference, 1984) during
testing of compliant-leaded HIC's: the bending moments applied to the
printed wiring board (PWB) and causing fracture of the hybrid integrated
circuit (HIC) turned out in some tests to be smaller when leads with
greater compliance were installed. It is shown that such a result is due
to the redistribution of the lead reactions at certain combinations of
the HIC length, HIC and PWB flexural rigidity, and lead spring-constant.
The analysis indicates that only sufficiently compliant leads can reduce
the stress in the HIC, while leads of moderate compliance can result in
even greater stresses than stiff leads. An easy-to-calculate governing
parameter that characterizes the mechanical behavior of HIC/PWB
assemblies with compliant leads is presented. The results can be of help
in physical design of compliant-leaded surface-mounted devices
A comparison was made of predicted and measured values of lead
stiffness for selected surface-mounted packages. Excellent agreement was
found in all cases: 68- and 44-lead plastic leaded chip carriers (PLCCs)
and cerquads (pressed ceramic quad flat pack); and 100-lead plastic quad
flat packs (PQFPs). Predictions were based on the 3D elastic beam
finite-element option of ANSYS, with lead geometries taken from design
drawings and lead elastic properties from material specifications.
Measured values were taken from straddle board test data. In these
tests, the board is straddled on both sides by packages surface mounted
by only their lateral or transverse leads so that lateral and transverse
bending effects can be measured independently. The results point out the
importance of low stiffness lead design in minimizing solder-joint
deformation
The stiffness of the "J" lead in plastic leaded chip carrier (PLCC) packages is calculated using simple beam bending theory. These results are compared with experimentally determined values and used to estimate shear stress amplitudes in the solder joint. Yielding loads in "J" leads of varying geometries are also determined.
The author provides equations for the directional spring constants
for common compliant lead designs on surface-mounted (SM) components.
The lead configurations include the straight J-lead, dimpled J-lead,
gull-wing lead, butt-lead, (I-lead), and S-bend lead designs. Elastic
strain energy methods were applied to determine the effective flexural
and torsional spring constants for each representative lead design. Lead
stiffness evaluation was performed for different SM components tested
using accelerated functional cycling and circuit-board dynamic bending.
Comparative compliance data are provided for the chip-carrier J-lead
designs in the Phase A IEEE Compliant Lead Task Force mechanical cycling
test program. The solder joint cycles-to-failure statistics indicate
that significant differences in attachment fatigue performance can be
correlated with disparate lead compliance between the tested SM
components. The structural models and strain energy formulation
presented provide a generalized method for quantifying the compliance of
common lead configurations. The resultant spring constants represent
mechanical properties of the particular lead design and are independent
of the SM package geometry and PCB (printed circuit board)
interconnection details
The reliability of the attachment of 100 I/O ceramic chip carriers
(CCs) surface mounted to FR-4 epoxy/glass circuit boards using
clip-leads has been investigated. Clip-leads, commercially available
from two vendors, of significantly different designs were utilized. The
accelerated tests involved the accurate reproduction of the thermal and
physical conditions-internal cyclic power dissipation, external thermal
cycling of forced air stream, thermal gradients, mounting hardware,
etc.-encountered by the product in use. The test acceleration (by
acceleration factors between 12 and 20 for mean time to failure) was
accomplished with shorter dwell times at the temperature extremes,
resulting in 96 accelerated fatigue cycles per day. The distinct
difference in lead compliancy between the two clip-lead designs is
clearly reflected in the results of the accelerated reliability tests.
The Type-A `J-lead design' clip-lead ( K =58 lb/in) CCs showed a
median life to failure of 12000 cycles, while the Type-B `hinged S-bend
design' clip-lead ( K =7.5 lb/in) CCs exhibited no failures when
the test was terminated at 100000 cycles. Failure mode analysis shows
that all Type-A clip-lead solder joints have failed after 48000
accelerated cycles due to the CC/substrate expansion mismatch: at 100000
accelerated cycles a significant number of clip joints showed cracks due
to the solder/ceramic CC material expansion differential
Life prediction of solder joints: Engineering mechan-ics methods Surface mount attachment reliability of clip-leaded ceramic chip carriers on FR-4 circuit boards
- B Sandor
B. 1. Sandor, " Life prediction of solder joints: Engineering mechan-ics methods, " in Solder Mechanics-A State of the Art Assess-ment, D. R. Frear, W. B. Jones and K. R. Kinsman, eds. TMS, W. Engelmaier, " Surface mount attachment reliability of clip-leaded ceramic chip carriers on FR-4 circuit boards, " in Proc. Nepcon Technical Program, Boston, MA, 1988, pp. 121-137.
Stiffness of PLCC 'J' lead and its effect on solder joint reliability
- J H Lau
J. H. Lau, " Stiffness of PLCC 'J' lead and its effect on solder joint reliability, " ASME Paper No. 87-WA/EEP, 12 pp.
Accelerated test methods for lead and solder joint integrity-An early assessment of three candidates Experimental constitutive relations for the high temperature deformation of a Pb-Sn eutectic alloy Comparison of predicted and measured lead stiffnesses of surface mounted packages
- W E Jahsman
- B Natarajan
- B P Kashyap
- G S Murty
- W E Jahsman
- P Jain
W. E. Jahsman and B. Natarajan, " Accelerated test methods for lead and solder joint integrity-An early assessment of three candidates, " Intel Rep., Oct. 1988. B. P. Kashyap and G. S. Murty, " Experimental constitutive relations for the high temperature deformation of a Pb-Sn eutectic alloy, " Mat. Sci. Eng., vol. 50, pp. 205-213, 1981. E. L. Crow, F. A. Davis, and M. W. Maxfield, Statistics Manual, New York: Dover, 1960. W. E. Jahsman and P. Jain, " Comparison of predicted and measured lead stiffnesses of surface mounted packages, " in Proc. 40th Com-ponents and Technology Conf., 1990, pp. 926-932.
Test method considerations for SMT solder joint reliability
- W Englemaier
Thermal, physical, electrical, mechanical and other properties of selected packaging materials
- P D Desai
- S K El-Rahaiby
- M S Deshpande
- R H Bogaard
- H H Li
- J F Chancy
- C Y Ho
Accelerated test methods for lead and solder joint integrityâAn early assessment of three candidates
- W E Jahsman
- B Natarajan
Load distribution analysis for plastic chip carriers under stress
- R C Landis
Mechanical characterization of J-bend leads and solder joints for surface mounted PLCCs
- W Huffman
- R Brownfield
- B Natarajan
Life prediction of solder joints: Engineering mechanics methods
- B I Sandor
- D R Frear
- W B Jones
- K R Kinsmanin
Chancy and C. Y. Ho Thermal, physical, electrical, mechanical and other properties of selected packaging materials
- P D Desai
- S K El-Rahaiby
- M S Deshpande
- R H Bogaard
- H H Li