Fig 1 - uploaded by B. Sammakia
Content may be subject to copyright.
Source publication
The Wafer Level-Chip-Scale Package (WLCSP) is designed to have external dimensions equal to that of the silicon device. This new package type is an extension of flip chip packaging technology to standard surface mount technology. The package has been targeted for low pin count (less than 30) and has high volume applications such as cellular phones,...
Contexts in source publication
Context 1
... due to elimination of lead frame and molding compound. 4) No underfill required and standard SMT assembly equip- ment and processing can be used. 5) High assembly yields can be realized from the self- aligning characteristic of the low mass die during solder attachment. A schematic of the cross section of a typical MicroCSP joint is shown in Fig. 1 after reflow ...
Context 2
... temperature range is changed from C to 125 C and 55 C to 150 C from 40 C to 125 C to study its effect on visco plastic strain energy density and solder fatigue life. The results are shown in Fig. 10. Ramp rate and dwell time are kept then same. As expected, the viscoplastic work increases as tem- perature range increases and thus the solder joint reliability de- creases. It is obvious that increasing the temperature range under practical test conditions is an effective way to reduce the time and cost of the reliability tests. The ...
Context 3
... [11]. Once the epoxy was cured, the sample and substrate were taken from the oven and the substrate was removed from the sample, leaving the grating attached to the sample. The sample then cooled to room temperature. An identical micro SMD sample was instrumented with a thermal couple and the cool down curve was recorded and is shown in Fig. ...
Context 4
... the part was cooled, it was placed into the interfer- ometer. After setup and calibration, the fringe shifting tech- nique was used to obtain a series of interference pattern images [10]. These were post-processed with the resulting computer en- hanced close-up of the fringe patterns shown in Fig. 13 repre- senting contours of horizontal displacement. Using the computer model to simulate the cool down from 100 C to room temperature (using the measured cool down curve shown in Fig. 12), the resulting relative horizontal dis- placement between top and bottom of the end-row solder joints was computed. For these packages, the ...
Context 5
... to obtain a series of interference pattern images [10]. These were post-processed with the resulting computer en- hanced close-up of the fringe patterns shown in Fig. 13 repre- senting contours of horizontal displacement. Using the computer model to simulate the cool down from 100 C to room temperature (using the measured cool down curve shown in Fig. 12), the resulting relative horizontal dis- placement between top and bottom of the end-row solder joints was computed. For these packages, the horizontal displacement (shear displacement) typically dominates the response and is a leading contributor to fatigue damage in the solder joint. This displacement is compared to that measured from ...
Context 6
... between top and bottom of the end-row solder joints was computed. For these packages, the horizontal displacement (shear displacement) typically dominates the response and is a leading contributor to fatigue damage in the solder joint. This displacement is compared to that measured from the moiré tech- nique. The end joint, shown circled above in Fig. 13, shows approximately five contours from the bottom to the top of the bump. Since each contour is 100.4 nm, the displacement of the end joint in horizontal direction is 502 nm. The quarter-sym- metric finite element model was built so that it had the same geometry as the cross-sectioned sample. The model was then loaded using the ...
Context 7
... five contours from the bottom to the top of the bump. Since each contour is 100.4 nm, the displacement of the end joint in horizontal direction is 502 nm. The quarter-sym- metric finite element model was built so that it had the same geometry as the cross-sectioned sample. The model was then loaded using the measured cool down curve of Fig. 11. The rela- tive displacement predicted by the model for the same bump was 552 nm. Comparing to the measured displacement, the model predicts a difference of approximately 10%. This is a satisfac- tory correlation and adds confidence in the solder constitutive ...
Citations
... For example, the materials and geometry, that define the package structure, have influence on the effective CTE of the package. Therefore, CTE is a function of the coefficients of thermal expansion of the materials, the thickness and the moduli of elasticity [11, 12]. As shown inFig. ...
The estimation of product reliability during the design is one of the key questions in microelectronics. The assembly lifetime is a function of such parameters as geometry, material properties and loads. All these influences exhibit systematic and stochastic variations. The effect of variability can be analysed by a probabilistic FE-simulation and statistical methods. This paper presents an approach for the prediction of thermal fatigue life of two CSP types, the μBGA and the QFN. Besides geometry parameters, also material properties and cycle temperatures are used as variable inputs. Based on a preliminary study the input parameters were defined as normal distributed. Sensitivities of the lifetime to the design parameters were computed and ranked after FE-simulations for both μBGA and QFN packages parameters had been performed. The fatigue life prediction of solder joints used in this work is based on a Coffin-Manson model and it was performed using the stress-strain data extracted from FE-simulations. As there exists a dependency on the solder deformation behaviour, the correct choice of the deformation model of lead-free solder alloys is an important aspect of this work. Summarising, in this work a probabilistic simulation method was developed to compute realistic failure distributions of two CSP types.
Solder reliability in LED assemblies is proven to be very critical for a reliable solid-state lighting system. Evaluation of the reliability in a fast way becomes a cutting edge of the industry, which can greatly diminish the design cycle and hence reduce the time to market. This chapter introduces two methodologies of doing fast reliability qualification of solder joint in LED assemblies: FEM-assisted lifetime estimation modeling and in situ high-precision fatigue damage-based lifetime prediction. These two methods can be also useful for RUL prognostic and quality screening test.
In this paper, the effects of newly defined solder geometric factors in a 2-pad LED lighting assembly on the reliability of Land Grid Array solder joints are investigated by adopting the methodology that we derived from our previous work. This has been done by conducting a series of FEM simulations to establish a response surface model for LED package geometric parameters to predict solder joint reliability. It shows that the LED carrier size (A) and solder coverage (SC) are the most influential factors. Decreasing the package size and increasing the solder coverage area can prolong the lifetime. Besides, it shows that the area ratio between two solder joints (AR) also affects the reliability greatly at large carrier size and solder coverage. It is found that in order to minimize the fatigue damage accumulation in the joints, a package design with a small carrier size, large solder coverage and equal pad size is preferable. Given the fact that the effect of SC is marginal in smaller packages, from a cost reduction point of view, intermediate solder coverage level is suggested.
The thermal cycling durability of large-area Pb-free (Sn3.5Ag) solder between silicon semiconductor and copper interconnects in photovoltaic (PV) cells is assessed and compared to benchmark results from Pb-based (Sn36Pb2Ag) PV cells. Accelerated thermal cycling tests have been conducted on PV cells of both solder compositions, and the increase in series resistance due to interconnect damage has been characterized using in situ dark I–V measurements. Both the Pb-free and Pb-based cells show a steep initial rise followed by a steady rate of increase in degradation histories, with the Pb-free cells showing a more pronounced ‘knee’ in the degradation curves. Extrapolation of the degradation data for both solders suggests that Pb-free cells are four times more durable than the Pb-based cells at the test condition. This superior thermal cycling fatigue durability of Pb-free cells was also confirmed with physics of failure (PoF) analysis, consisting of nonlinear finite element (FE) stress analysis and an energy-partitioning (E-P) solder fatigue model. FE models error-seeded with manufacturing voids in the solder interconnect predicted a significant reduction in the thermal cycling durability with increasing solder void density. However, even the most voided Pb-free cells modeled are predicted to be twice as durable as void-free Pb-based cells, under the accelerated temperature cycle used in the test. The acceleration factor (AF) predicted by the PoF analysis for a typical service environment is three times higher for Pb-free cells than that for Pb-based cells. Copyright © 2010 John Wiley & Sons, Ltd.
To increase miniaturization, CSWLP (chip size wafer level packaging) has been developed. However, the difficulty to get good solder joint reliability leads to manufacture only small CSWLP modules. Different underfill methods are evaluated here, by measurements and simulations: results prove that underfill is necessary, but a bad choice can also decrease the reliability. An original method called ldquore-enforcementrdquo improves the life time.
