Package Cracking Research Articles

Investigation on memory package crack and prevention under temperature cycling test

Memory package with multiple die stacking in one package faced package crack issue during package level temperature cycling test (TCT) and the failure cycle cannot meet reliability requirement. Failure analysis showed epoxy molding compound (EMC) cracking located at the center area of package surface. Finite element modeling and simulation was conducted to study package stress and failure mechanism under cyclic temperature loading condition. Simulation results showed that the center of package surface is subjected to higher stress and stress variation during stringent TCT test due to high and tight die stacking structure. Several parametric studies were conducted to further understand failure mechanism and provide solution for crack prevention. Design guideline was proposed to eliminate or reduce package crack risk for multi-chip package (MCP) in memory chip package.

Study of the Impact of Curing Condition on Flexural Strength of a Very Thin Semiconductor Package

Thinner semiconductor package is becoming popular especially in consumer electronics applications. As package becomes thinner, it is more vulnerable to package crack when subjected to external load. It is important to ensure that the package is strong enough to resist package cracking. This paper presents the study of package flexural strength under different epoxy mold compound curing condition. A 3-point bend test was done to characterize the breaking strength of the package that was subjected to post-mold curing. It was then compared to the strength of the package not subjected to post-mold curing (PMC). Results of the bend testing showed that the package flexural strength is much lower when the package is not subjected to post-mold curing. This study demonstrates that the measurement of flexural strength can be used to determine if the package has undergone post-mold curing or not. Performing the right post-mold curing of the thin molded package is required to ensure higher flexural strength.

Understanding Package Crack Signatures in a Leadframe Semiconductor Package

This paper presents the simulation approach used to understand package crack signatures of a leadframe package under different mechanical loading scenarios. Package crack is one of the common problems with semiconductor packages. A better understanding of the different crack signatures would help identify the root cause quickly and be able to find the correct solution. In this study, a high precision materials testing system was used to apply mechanical loading to the package simulating different scenarios that could produce the crack. Based on the testing results, cracks have distinct signatures depending on how the force is applied. With the different signatures identified, this approach makes it easy to find the root cause of the crack in actual applications or assembly processes and resolve the problem faster.

Stress Modeling Study on Package Crack Due to Debris

Very thin semiconductor package is very prone to package crack. This paper discusses the stress modeling study conducted to understand the package crack problem in a specific smart card package. Finite element analysis (FEA) was used to analyze the maximum package stress level and corresponding location to find out if the presence of debris during the package assembly punching process could cause such problem and how it would happen. Based on the stress results, it was confirmed that even with a 60μm-thick piece of debris under the package, crack at the top is possible due to package bending and mold stress exceeding the flexural strength of the package mold material. The stress increases as the debris location is moved closer to the area where force is applied during the punching process. The study shows that the presence of debris should not be taken for granted though how small the debris may seem because significantly high bending stress could still be induced especially for very thin packages. Eliminating any source of debris in the package assembly process.is very important to prevent package crack.

Nanotechnologies: Risk assessment model

The development and use of nanomaterials has grown widely in the last years. Hence, it is necessary to carry out a careful and aimed risk assessment for the safety of the workers.The objective of this research is a specific assessment model finalized to the workplaces where the personnel work manipulating nanoparticles. This model mainly takes into account the number of exposed workers, the dimensions of particles, the information found in the safety data sheets and the uncertainties about the danger level coming from the exposition to nanomaterials. The evaluation algorithm considers the normal work conditions, the abnormal (e.g. breakdown air filter) and emergency situations (e.g. package cracking). It has been necessary to define several risk conditions in order to quantify the risk by increasing levels ("low", "middle" and "high" level). Each level includes appropriate behavioural procedures. In particular for the high level, it is advisable that the user carries out urgent interventions finalized to reduce the risk level (e.g. the utilization of vacuum box for the manipulation, high efficiency protection PPE, etc). The model has been implemented in a research laboratory where titanium dioxide and carbon nanotubes are used. The outcomes taken out from such specific evaluation gave a risk level equal to middle.

Predicting the process induced warpage of electronic packages using the P– V– T– C equation and the Taguchi method

A critical issue in the manufacturing of electronic packages is the warpage induced during the molding process as a result of differences in the shrinkage of the constituent materials. Package warpage causes serious problems such as the quality degradation of devices and yield loss in manufacturing processes. Loss of lead coplanarity happens due to package warpage and causes difficulty in device testing and surface mount assembly. Internal stresses associated with package warpage can also cause device failures such as die cracking, broken circuits and package cracking. Warpage in IC package has drawn intensive attention in the past. Although the effects of thermal shrinkage were extensively investigated in the literatures, the influence of the cure shrinkage on package warpage had received less attention. Accordingly, this study develops a numerical approach for generating more accurate predictions of the package warpage by taking the effects of both thermal shrinkage and cure shrinkage into account. A three-dimensional finite element model of the small outline package (TSOP) DBS-27P is constructed and the proposed numerical approach, which is based on the P– V– T– C (pressure–volume–temperature–conversion) equation and the CTEs (coefficients of thermal expansion) of the package materials, is employed to predict the warpage at each of its corners under various packaging processing conditions. Using the Taguchi method, the relative influences of the transfer pressure, the packing pressure, the mold temperature and the curing time on the degree of package warpage are identified and the optimal processing conditions are established. A series of experimental packaging trials are performed using the optimal processing conditions. It is found that the warpage of the actual package is in good agreement with that predicted numerically. Therefore, the accuracy of the proposed numerical approach is confirmed. Moreover, the results also demonstrate the capability of the Taguchi method to identify the optimal packaging processing parameters on the basis of a limited number of simulation runs.

The effect of hygro-mechanical and thermo-mechanical stress on delamination of gold bump

The reliability of the FC–CSP (flip chip–chip scaled package) package with gold bump at the MRT (moisture resistance test) reflow temperature, was evaluated by using the finite element method. The moisture properties of EMC (epoxy molding compound) obtained from the test described in JEDEC standard, were used to characterize the local moisture concentration analysis by transient moisture diffusion, the hygro-mechanical analysis by CME, the vapor pressure analysis and the thermo-mechanical analysis by CTE mismatch. Also, after precondition, the package reliability under the reflow process was predicted, by comparing and integrating each factors, package swelling and stress due to by vapor pressure, as well as thermo-mechanical stress. Consequently, the result showed that the effects on hygro-mechanical stress and vapor pressure in a package could not be negligible, when it is compared with that of the thermo-mechanical stress by CTE mismatch, which is recognized as the main effect on the package crack under reflow temperature. The stress was concentrated at interface between gold bump and die, where most of delamination occurred.

The package CRACK for solving large overdetermined systems

The program CRACK is a computer algebra package written in REDUCE for the solution of over-determined systems of algebraic, ordinary or partial differential equations with at most polynomial non-linearity. It is available as part of version 3.8 of the REDUCE system (dated April 2004) and the latest development version can be downloaded from http://lie.math.brocku.ca/crack/. The purpose of this poster is to accompany a software demonstration of CRACK at ISSAC 2005. The poster is supposed to give a graphical overview of CRACK, emphasizing features which are special to the package. Those are • a rich interface, with visualization aids for inspecting large systems, including - for each equation its properties, history and investigations that have already been done with the equation, - the occurrence of all derivatives of selected functions in any equation, - a statistical overview of the system (number of equations and functions in dependence of number of independent variables), - a matrix display of occurrences of unknown constants/functions in all equations, - a count of the total number of appearances of each unknown, - the determination of not under-determined subsystems, - a listing of all sub- and sub-sub-.. cases investigated so far, with their assumptions, number of steps and number of solutions, - graphical displays of size related measures of the computation done so far; • a discussion of possibilities to trade interactively or automatically the speed of the solution process versus safety (avoidance of expression swell): - only length-reducing versus complete Gröbner basis computation steps. - substitutions in shorter equations only, i.e. only in a sub-system versus substitutions in the complete system, - growth bounded substitutions versus general substitutions, - case splittings (induced by factorizations, substitutions with potentially vanishing coefficients or adhoc case distinctions) versus Gröbner basis steps, - an investment in the length reduction of equations to reach sparse systems with multiple benefits; • algorithmic extensions which include - the ability to collect and apply syzygies which result as a by-product in the process of computing a differential Gröbner basis to integrate linear PDEs. - the treatment of inequalities: their usage, active collection and derivation, and their constant update in an ongoing reduction process based on newly derived equations. - the capability added by Winfried Neun (ZIB Berlin) to run in a truly parallel mode on a beowulf cluster, recently also ported to 64bit AMD processors. - post-computation procedures, especially the possibility to merge solutions of parametric linear algebraic systems and to automate the production of web-pages for solutions that are found. - the ability to separate expressions with respect to independent variables which occur polynomially but with variable exponents, leading to automatically investigated case distinctions of exponents being equal or not; • safety enhancing measures as - the ability to backup and re-load the whole session, - the automatic storing of the complete keyboard input during a session with the opportunity to feed this stored input into a new session, - the possibility to impose time restrictions of notoriously slow sub-steps, like factorizations and sometimes the computation and reduction of S-polynomials in a Gröbner basis computations, - a method to interrupt an ongoing automatic computation and change it to interactive mode The poster in landscape format will display the above four topics in boxes. For some of the sub-items above a screen output will give a visual impression, like the matrix indicating occurrences of unknowns in equations. In the following publications the solution of large overdetermined systems was a crucial ingredient: • the solution of large bi-linear algebraic systems and automatic merging of obtained solutions: - Wolf, T., Efimovskaya, O. V.: Classification of integrable quadratic Hamiltonians on e(3), Regular and Chaotic Dynamics, vol 8, no 2 (2003), p 155--162. - Sokolov, V. V., Wolf, T.: Classification of integrable polynomial vector evolution equations, J. Phys. A: Math. Gen. 34 (2001) 11139--11148. - Tsuchida, T. and Wolf, T.: Classification of integrable coupled systems with one scalar and one vector unknown, preprint nlin.SI/0412003 (2004) 60 pages, to appear in J. Phys. A: Math. Gen. - Sokolov, V. V. and Wolf, T.: Integrable quadratic Hamiltonians on <i>so</i>(4) and <i>so</i>(3, 1), preprint (2004) 16 pages, nlin.SI/0405066. - Kiselev, A. and Wolf, T.: New recursive chains of N=1 homogeneous superequations, to appear in proceedings of "Symmetry in Nonlinear Mathematical Physics", Kyiv 2005. • the solution of extensive overdetermined ODE/PDE-systems: - Anco, S. and Wolf, T.: Some symmetry classifications of hyperbolic vector evolution equations, nlin.SI/0412015, JNMP, Volume 12, Supplement 1 (2005), p 13--31.

Vapor Pressure and Residual Stress Effects on Mixed Mode Toughness of an Adhesive Film

Temperature- and moisture- induced delamination leading to popcorn package cracking is a major package reliability issue for surface-mount plastic encapsulated microcircuits (PEM). Crack propagation along one of the interfaces of a ductile adhesive joining two elastic substrates is modeled to study interface delamination and toughness of PEMs. The polymeric adhesive is stressed by remote loading and residual stress. Along the crack front, the film-substrate interface is modeled by a strip of cells that incorporates vapor pressure effects on void growth and coalescence through a Gurson porous material relation. Results show that under high levels of vapor pressure, increasing film thickness will produce smaller enhancement on the steady-state fracture resistance of the interface, also referred to as the joint toughness. Across all mode mixity levels, vapor pressure effects dominate over residual stress. The adverse effects of vapor pressure are greatest in highly porous adhesives subjected to a strong mode II component. The latter is representative of the likely state of loading in IC packages since residual stress, resulting from the film-substrate thermal mismatch, induces a predominantly mode II component.

Vapor pressure assisted crack growth at interfaces under mixed mode loading

Moisture diffuses into the numerous pores and cavities formed in polymeric molding compounds, at the filler particle–polymer matrix interfaces and at polymer–silicon interfaces of IC packages. During reflow soldering, the rapidly expanding moisture generates high internal pressures within the voids which are comparable to yield strengths of the molding compounds at glass transition temperatures. The combined action of thermal stresses and high vapor pressure accelerates void growth, and ultimately leads to interface delamination and package cracking. In this study, the molding compound is taken to be an elastic–plastic material while the silicon substrate is treated as an elastic material. The extended Gurson model which incorporates vapor pressure as an internal variable is used to characterize the void growth and coalescence process at the interface. When the mode II loading is dominant, high vapor pressure can cause several-fold reduction in the interface fracture toughness.

On the mode II popcorn effect in thin packages

Experiments were carried out using P-TQFP-176 packages to study the mode II popcorn effect in thin packages. The doming of the package backside was measured as a function of time and temperature. The measurements were performed using a line projection method. An accelerated increase in the doming was found to correlate with the onset of the package crack propagation. It was shown that when a constant critical doming angle is reached, package cracks begin to propagate toward the surface. This critical doming angle was found to be temperature independent between 170/spl deg/C and 215/spl deg/C. Furthermore the development of the package doming with time was described by a simple model based on the moisture diffusion from molding compound and die-attach material in combination with a bimaterial plate theory. The water content of the die-attach layer after preconditioning was calculated from the model and it was found to be in good agreement with the results of a three dimensional finite element simulation.

Reliability of plastic ball grid array package

The reliability of plastic ball grid array (PBGA) package is studied for different materials. The reliability of the PBGA packages using conventional Bismaleimide-Triazine type PWB and our original product PWB that is made of high Tg epoxy resin is evaluated. The PBGA package using our original PWB has a feature of lower warpage for the package, and has similar performance regarding the thermal cycling stability and the endurance during reflow soldering as compared with the PBGA using the conventional PWB. The endurance during reflow soldering for each PBGA is JEDEC STD Method A112 level 3. In order to improve the endurance during reflow soldering, not only PWB materials but also other factors are investigated. As a result, the molding compound with the property of low moisture absorption and the die attach material with the properties of high adhesion strength and fracture strength are effective to improve the endurance property during reflow soldering. The package crack mechanism during reflow soldering is briefly described as follows.

Thermal and vapor pressure effects on cavitation and void growth

Vapor pressure and thermal stress induced growth and coalsecence of microvoids near interfaces of die/die-attach and die-pad/moulding compound is recognised as the precursor to interface delamination and popcorn cracking of plastic electronic packages. When exposed to humid ambient conditions prior to reflow soldering, plastic electronic packages absorb moisture, which condenses within the numerous micropores in the substrate, die attach, moulding compounds and in the vicinity of interfaces joining the different material layers. During reflow soldering, moisture in these micropores is vaporized. A representative material cell containing a single microvoid is used to investigate void growth under combined vapor pressure and thermal stress. A critical surface traction, the sum of the internal vapor pressure and the externally applied stress, defines the onset of unstable void growth. Existence of “large” microvoids lowers significantly the critical stress levels for unstable void growth. These stress levels are consistent with generally accepted estimates of stress levels for popcorn cracking given in the literature. Vapor pressure effects can be incorporated into a continuum description of stresses and strains and the Gurson-Tvergaard void growth model providing a new capability for full-field analysis of popcorn cracking in electronic packages.

Effect of Thermal Stress on Cracking of IC Plastic Packages during Reflow Soldering.

Cracking mechanism in IC plastic packages during reflow soldering was analyzed considering both vapor pressure and thermal stress. The vapor pressure induced stress, which was considered as the dominant factor for the IC package cracking, strongly depends on the total amount of absorbed water. The IC package cracking was observed, even when the vapor pressure induced stress was much lower than the strength of the molding compound, which was almost constant at temperatures above 200°C. The cracking was found to occur when the total amount of the stress, which was caused not only by the vapor pressure but also by thermal stress, reached the strength of the moling compound. Therefore, thermal stress is also the important factor for IC package cracking during reflow soldering.

Properties of molding compounds to improve package reliability of SMDs

Package cracking during reflow soldering process is the great problem in the reliability of plastic packages. The technique of lowering the glass transition temperature (Tg) of a molding compound is very effective for improvement of the package cracking resistance because of the properties of low moisture absorption and high adhesion strength for a molding compound. But the package reliability except for the package cracking resistance is also important. In this study, the effects of the Tg for molding compounds on the package reliability was discussed. It was confirmed that decreasing the crosslinking density was an important factor to improve the package cracking resistance. There was no problem in thermal resistance, even if the molding compound has low Tg. However, decreasing the crosslinking density by the lowering of Tg may not satisfy humidity resistance in some cases. It was found to be important to decrease the crosslinking density of molding compounds without lowering Tg in order to improve both the package cracking resistance and the humidity resistance. It was also confirmed that the introduction of rigid structural segments into the matrix resin molecules of the molding compound was a useful technique for achieving excellent package reliability.

Investigation of stress singularity fields and stress intensity factors for cracks

The reliability of semiconductor devices and packages used in microelectronics is compromised by interfacial delamination and homogenous cracking that is initiated at the edge of the interface between dissimilar materials during processing and stress tests. These failures have certain characteristics in that they begin at the stress singularity point. The knowledge of interfacial fracture mechanics is very important to the design for reliability of these devices and packages. In this paper, a model of stress singularity is proposed and applications of the model for the characterization of interfaces are subsequently presented. Examples are integrated circuit (IC) device interfaces and plastic package interfaces. These interfaces were mainly characterized with the order of stress singularity. Furthermore, this study demonstrates applications of the stress intensity factors for the stress singularity fields. The stress intensity factors were obtained from a r– θ coordinate system, the order of stress singularity, the Dunders' parameters, and the extrapolation as a function of distance. The relationship between the stress intensity factors and the fracture toughness strength of molding compound as a function of mode mixed was also investigated for cracking at the edge of the interface. The proposed numerical scheme was verified by the experiments on the lead-on-chip (LOC) package crack under temperature cyclic loads.

Effect of geometric parameters on popcorn cracking in plastic packages during VPS process

Several thin quad flat packages (TQFPs) are analyzed for the evaluation of G, the energy release rate based on the interfacial fracture mechanics. The purposes of this study are; (i) to obtain the values of G as a function of the length of delamination (interfacial crack) and various geometric dimensions, (ii) to obtain the values of G for the package crack, which is believed to be the subsequent stage to the full delamination, and consequently (iii) to investigate quantitatively the effect of the various geometric dimensions on the popcorn cracking during vapor-phase soldering (VPS). Also the method to compute the phase angle (or mode mixity) for the interfacial crack is presented for several TQFPs. Due to the insufficient data for G c int, the question of whether the partial delamination for given a (delamination length or crack length) grows or not cannot be addressed. However, this can be used for the prediction of the popcorn cracking in the future study.

A study of soldering heat evaluation for SMDs

Environmental factors affecting package crack occurrence are: • -humid atmosphere and time; • -soldering heat method and the number of times; • -heating temperature and time, etc. As mounting styles have become diversified, the above environmental conditions have been included in customer's quality requirements. Therefore, reasonable soldering heat evaluation methods are required. This paper demonstrates that resistance to package crack of a package made of a highly adhesive mold resin can be explained in terms of the Interface moisture content and maximum temperature applied to the package only.

Analyses of Delamination Arrest Effect of Dimples on Interface in LSI Package

The delamination arrest between die pad and resin should be an efficient method to prevent resin cracking of LSI packages. In some LSI packages, dimples arranged on the die pad are effective for delamination arrest. In this study, the effects of dimples on delamination arrest are examined based on boundary element analyses of LSI packages under conditions of thermal and steam pressure loading. To evaluate this effect, the stress intensity factor, K i , for an interface crack was calculated using the contact between interface crack surfaces. The following main results were obtained. (1) The dimple decreases K i under both thermal and steam pressure load conditions. (2) The main reason for decreasing K i is to prevent shearing deformation between crack surfaces under thermal load conditions. Conversely, the reason for the decrease is the kinking of interface crack tips under steam pressure load conditions. (3 ) The effect of delamination arrest increases as the dimple depth increases.

Estimate of package crack reliabilities on the various parameters using taguchi's method

Package crack caused by the soldering process in the surface mounting plastic package is evaluated by applying the maximum energy release rate criterion. It could be shown that the crack propagation from the lower edge of the ie pad is easily occurred at the maximum temperature during the soldering process, where the pressure acting on the crack surface is assumed by the saturated vapor pressure at maximum temperature. The package crack formation depends on various parameters such as chip size, relative thickness, material properties, the moisture content and soldering temperature etc. The quantitative measure of the effects of the parameters could be easily obtained by using the taguchi's method which requires only a few kinds of combinations with such parameters. From the results, it could be obtained that the more significant parameters to effect the package reliability are the orders of Young's modulus, die pad size, down set, chip thickness and maximum soldering temperature.