Reflow Behavior and Board Level BGA Solder Joint Properties of Epoxy Curable No-clean SAC305 Solder Paste

Thin Small Outline Package (TSOP) are one of the most commonly used surface mount components due to its low overall cost. Traditionally leadframe packages such as TSOP or Quad Flat Package (QFP) are less of a concern (if assembled with SnPb eutectic solder paste) about their long term reliability and often exempted from board level qualification testing as the mechanical compliance of metal leads mitigate the stresses due to the Coefficient of Thermal Expansion (CTE) mismatch between the package and Print Circuit Board (PCB). Therefore more attention has been put on the solder joint reliability of Pb-free Ball Grid Array (BGA) packages over leadframe packages while the industry is moving away from SnPb eutectic solder materials to meet RoHS regulatory requirements. The authors have observed that TSOPs if assembled with Pb-free solder materials could fail at very early stages during qualification testing (in some case as early as 300 cycles under standard 0°C to 100°C thermal cycling). Since most Pb-free solder materials such as SnAgCu are mechanically more rigid than SnPb eutectic solder material, higher stresses are expected be induced in solder joints during temperature excursions. Pb-free solder materials’ wicking behavior may also contribute to the early failures. In this study, long term reliability of a flash memory TSOP has been investigated. These tested TSOPs, assembled on 93mil-thick PCBs with SAC305 paste, are of two configurations: one with single die and the other with stacked quadruple dies. Some test vehicles have been thermally aged under four different thermal aging conditions to study the aging effect on Pb-free solder joint life. Finite element analysis (FEA) modeling has also been employed to further investigate the impact of other parameters such as die size, package size, and the number of dies that being stacked inside one package.

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Controlling the Superior Reliability of Lead Free Assemblies With Short Standoff Height Through Design and Materials Selection

Volume 9: Micro- and Nano-Systems Engineering and Packaging, Parts A and B ◽

10.1115/imece2012-89584 ◽

2012 ◽

Cited By ~ 3

Author(s):

B. Arfaei ◽

L. Wentlent ◽

S. Joshi ◽

M. Anselm ◽

P. Borgesen

Keyword(s):

Solder Joint ◽

Electron Backscatter Diffraction ◽

Grain Morphology ◽

Superior Performance ◽

Solder Paste ◽

Materials Selection ◽

Sac305 Solder ◽

Solidification Temperature ◽

Snagcu Solder ◽

Systematic Effects

We have recently demonstrated a significantly longer life in accelerated thermal cycling for Land Grid Arrays (LGAs) assembled only with SAC305 solder paste than for the corresponding SAC305 based BGA assemblies. This superior performance was shown to be a direct effect of the solder microstructure. The final Sn solidification temperature strongly affects the initial microstructure of a SnAgCu solder joint, including the Sn grain morphology, and thus the thermomechanical behavior of the joint. Right after reflow, larger BGA joints of SnAgCu alloys, which solidify at higher temperature, reveal either a single β-Sn grain or three large grains with clearly defined boundaries formed by cyclic twinning. The orientations of the highly anisotropic Sn grains are not yet controllable in manufacturing, leading to substantial statistical scatter in the performance of the solder joints. Typical LGA solder joint dimensions, however, tend to facilitate greater undercooling and the formation of an alternative interlaced twinning microstructure. A systematic study was undertaken to identify the parameters that control the interlaced twinning microstructure. Sn grain structures were characterized by crossed polarizer microscopy and electron backscatter diffraction (EBSD). Precipitate sizes and distributions were measured using backscattered scanning electron microscopy and quantified using image analysis software. Systematic effects of solder alloy, dimensions and pad finishes were identified. Recommendations are made as to design and materials selection. The practicality of controlling the desired microstructure, as well as potential disadvantages for certain applications is discussed.

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Microstructural evolution and micromechanical properties of SAC305/CNT/CU solder joint under blast wave condition

Soldering & Surface Mount Technology ◽

10.1108/ssmt-11-2019-0035 ◽

2020 ◽

Vol 33 (1) ◽

pp. 47-56

Author(s):

Norliza Ismail ◽

Azman Jalar ◽

Maria Abu Bakar ◽

Nur Shafiqa Safee ◽

Wan Yusmawati Wan Yusoff ◽

...

Keyword(s):

Solder Joint ◽

Blast Wave ◽

Microstructural Evolution ◽

Circuit Board ◽

Solder Paste ◽

Sac305 Solder ◽

Wave Condition ◽

Content Type ◽

Micromechanical Properties ◽

Sac Solder

Purpose The purpose of this paper is to investigate the effect of carbon nanotube (CNT) addition on microstructure, interfacial intermetallic compound (IMC) layer and micromechanical properties of Sn-3.0Ag-0.5Cu (SAC305)/CNT/Cu solder joint under blast wave condition. This work is an extension from the previous study of microstructural evolution and hardness properties of Sn-Ag-Cu (SAC) solder under blast wave condition. Design/methodology/approach SAC/CNT solder pastes were manufactured by mixing of SAC solder powder, fluxes and CNT with 0.02 and 0.04 by weight percentage (Wt.%) separately. This solder paste then printed on the printed circuit board (PCB) with the copper surface finish. Printed samples underwent reflow soldering to form the solder joint. Soldered samples then exposed to the open field air blast test with different weight charges of explosives. Microstructure, interfacial IMC layer and micromechanical behavior of SAC/CNT solder joints after blast test were observed and analyzed via optical microscope, field emission scanning microscope and nanoindentation. Findings Exposure to the blast wave induced the microstructure instability of SAC305/Cu and SAC/CNT/Cu solder joint. Interfacial IMC layer thickness and hardness properties increases with increase in explosive weight. The existence of CNT in the SAC305 solder system is increasing the resistance of solder joint to the blast wave. Originality/value Response of micromechanical properties of SAC305/CNT/Cu solder joint has been identified and provided a fundamental understanding of reliability solder joint, especially in extreme conditions such as for military applications.

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Influence of Intermetallic Characteristics on the Solder Joint Strength of Halogen-Free Printed Circuit Board Assembly

Journal of Electronic Packaging ◽

10.1115/1.4003989 ◽

2011 ◽

Vol 133 (2) ◽

Cited By ~ 2

Author(s):

Hung-Jen Chang ◽

Jung-Hua Chou ◽

Tao-Chih Chang ◽

Chau-Jie Zhan ◽

Min-Hsiung Hon ◽

...

Keyword(s):

Solder Joint ◽

Printed Circuit Board ◽

Circuit Board ◽

Solder Paste ◽

Sac305 Solder ◽

Printed Circuit ◽

Pull Strength ◽

Free Solder ◽

Halogen Free ◽

Electroless Ni

Five halogen-free (HF) dummy plastic ball grid array (PBGA) components with daisy-chains and Sn4.0Ag0.5Cu (SAC405) Pb-free solder balls were assembled on a HF high density interconnection (HDI) printed circuit board (PCB) using Sn1.0Ag0.5Cu (SAC105) and Sn3.0Ag0.5Cu (SAC305) Pb-free solder pastes, respectively. The above compositions were in weight percent. The assemblies were then experienced to moisture sensitive level testing with three times reflow at a peak temperature of 260 °C; no delamination was found present in both the component and PCB laminates. The microstructure showed that the utilization of SAC105 solder paste was beneficial in refining the Ag3Sn intermetallic compound (IMC) within the solder joint and the intermetallic layers formed at various interfaces with different Ni contents and thicknesses due to different metal finishes. The IMC spalling was found at the BGA-side interface within the solder joints formed with SAC105 solder paste but not discovered within the ones made of SAC305 solder paste. The pull strength of the solder joint formed with SAC305 solder paste was always higher than that made from SAC105 no matter on Cu or electroless Ni. Moreover, the fracture was found at the interface between the Cu foil and epoxy in the halogen-free test device. Numerical analysis showed that the thickness of IMC layer dominated the pull strength of the solder joint because the Z-axial normal stress applied to the solder joints formed with Cu and electroless Ni were 752.0 and 816.6 MPa, respectively, and a thicker IMC layer was beneficial to provide a higher pull strength of solder joint.

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Reliability of PCB Solder Joints Assembled with SACm™ Solder Paste

International Symposium on Microelectronics ◽

10.4071/isom-tp65 ◽

2014 ◽

Vol 2014 (1) ◽

pp. 000367-000373 ◽

Cited By ~ 1

Author(s):

Arnab Dasgupta ◽

Fengying Zhou ◽

Christine LaBarbera ◽

Weiping Liu ◽

Paul Bachorik ◽

...

Keyword(s):

Solder Joint ◽

Thermal Aging ◽

Test Performance ◽

Solder Joints ◽

Ductile Failure ◽

Drop Test ◽

Bulk Property ◽

Solder Paste ◽

Fatigue Reliability ◽

Sac305 Solder

The solder alloy SACm™0510 has been reported to be a superior alloy when used as BGA balls, exhibiting not only an outstanding drop test performance when compared to SAC105, but also as having high thermal fatigue reliability when compared to high Ag SAC solders. In this study, SACm0510 solder was evaluated as a solder paste. The voiding behavior of SGA solder joints was comparable for SACm0510, SAC105, and SC305. When evaluating SGA assemblies on a customized drop test, SACm0510 outperformed SAC105 considerably, which in turn was much better than SAC305. The drop test performance was found to improve upon thermal aging at 150°C, and the difference between the alloys reduced significantly. This was explained by the speculated grain coarsening which resulted in a softened solder joint, and consequently, a shift of fracture mode from brittle failure toward ductile failure. This model was supported by the observation of the fractured surface moving away from the interface upon thermal aging. The improvement in drop test performance upon thermal aging can be further explained by the large solder joint size of the SGA employed in this study, where the bulk property of solder weighed more than a small solder joint. When the assembled chip resistors were evaluated with a −55°C/+125°C TCT test, no failure was observed after 369 cycles for all three alloys. SAC305 appeared to be the best in maintaining the integrity of the interfacial IMC layer. SACm0510 showed a few crack lines, but less than that of SAC105. SACm0510 solder paste was found to be very compatible with BGAs with SAC305 solder joints, and no abnormal microstructure was observed after thermal aging at 150°C for 1000 hours.

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Study on the Reliability of Sn–Bi Composite Solder Pastes with Thermosetting Epoxy under Thermal Cycling and Humidity Treatment

Crystals ◽

10.3390/cryst11070733 ◽

2021 ◽

Vol 11 (7) ◽

pp. 733

Author(s):

Lu Liu ◽

Songbai Xue ◽

Ruiyang Ni ◽

Peng Zhang ◽

Jie Wu

Keyword(s):

Solder Joint ◽

Thermal Cycling ◽

Composite Solder ◽

Solder Joints ◽

Solder Paste ◽

Epoxy System ◽

Mechanical Reinforcement ◽

Microstructure Observation ◽

Temperature And Humidity ◽

Thermosetting Epoxy

In this study, a Sn–Bi composite solder paste with thermosetting epoxy (TSEP Sn–Bi) was prepared by mixing Sn–Bi solder powder, flux, and epoxy system. The melting characteristics of the Sn–Bi solder alloy and the curing reaction of the epoxy system were measured by differential scanning calorimeter (DSC). A reflow profile was optimized based on the Sn–Bi reflow profile, and the Organic Solderability Preservative (OSP) Cu pad mounted 0603 chip resistor was chosen to reflow soldering and to prepare samples of the corresponding joint. The high temperature and humidity reliability of the solder joints at 85 °C/85% RH (Relative Humidity) for 1000 h and the thermal cycle reliability of the solder joints from −40 °C to 125 °C for 1000 cycles were investigated. Compared to the Sn–Bi solder joint, the TSEP Sn–Bi solder joints had increased reliability. The microstructure observation shows that the epoxy resin curing process did not affect the transformation of the microstructure. The shear force of the TSEP Sn–Bi solder joints after 1000 cycles of thermal cycling test was 1.23–1.35 times higher than the Sn–Bi solder joint and after 1000 h of temperature and humidity tests was 1.14–1.27 times higher than the Sn–Bi solder joint. The fracture analysis indicated that the cured cover layer could still have a mechanical reinforcement to the TSEP Sn–Bi solder joints after these reliability tests.

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Experimental Investigation by Speckle Interferometry of Solder Joint Failure Under Thermomechanical Load Aggravated by Boundary Conditions at Board Level

Journal of Electronic Packaging ◽

10.1115/1.4007812 ◽

2012 ◽

Vol 134 (4) ◽

Cited By ~ 5

Author(s):

D. N. Borza ◽

I. T. Nistea

Keyword(s):

Solder Joint ◽

Fundamental Frequency ◽

Printed Circuit Board ◽

Speckle Interferometry ◽

Circuit Board ◽

Joint Failure ◽

Printed Circuit ◽

Out Of Plane ◽

Fringe Patterns ◽

Board Level

Reliability of electronic assemblies at board level and solder joint integrity depend upon the stress applied to the assembly. The stress is often of thermomechanical or of vibrational nature. In both cases, the behavior of the assembly is strongly influenced by the mechanical boundary conditions created by the printed circuit board (PCB) to casing fasteners. In many previously published papers, the conditions imposed to the fasteners are mostly aiming at an increase of the fundamental frequency and a decrease of static or dynamic displacement values characterizing the deformation. These conditions aim at reducing the fatigue in different parts of these assemblies. In the photomechanics laboratory of INSA Rouen, the origins of solder joint failure have been investigated by means of full-field measurements of the flexure deformation induced by vibrations or by forced thermal convection. The measurements were done both at a global level for the whole printed circuit board assembly (PCBA) and at a local level at the solder joints where failure was reported. The experimental technique used was phase-stepped laser speckle interferometry. This technique has a submicrometer sensitivity with respect to out-of-plane deformations induced by bending and its use is completely nonintrusive. Some of the results were comforted by comparison with a numerical finite elements model. The experimental results are presented either as time-average holographic fringe patterns, as in the case of vibrations, or as wrapped phase patterns, as in the case of deformation under thermomechanical stress. Both types of fringe patterns may be processed so as to obtain the explicit out-of-plane static deformation (or vibration amplitude) maps. Experimental results show that the direct cause of solder joint failure may be a high local PCB curvature produced by a supplementary fastening screw intended to reduce displacements and increase fundamental frequency. The curvature is directly responsible for tensile stress appearing in the leads of a large quad flat pack (QFP) component and for shear in the corresponding solder joints. The general principle of increasing the fundamental frequency and decreasing the static or dynamic displacement values has to be checked against the consequences on the PCB curvature near large electronic devices having high stiffness.

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Use-Conditions-Based Board Level Shock Test Development for Handheld Components

Electronic and Photonic Packaging, Electrical Systems Design and Photonics, and Nanotechnology ◽

10.1115/imece2004-60121 ◽

2004 ◽

Author(s):

Shubhada Sahasrabudhe ◽

Vinayak Pandey ◽

Betty Phillips ◽

Kang Joon Lee ◽

Lei Mercado

Keyword(s):

Solder Joint ◽

Cell Phone ◽

Standardized Test ◽

Test Development ◽

Failure Mechanisms ◽

Reliability Test ◽

Shock Test ◽

Board Level ◽

Test Repeatability

For handheld electronic applications such as cell phones and Personal Digital Assistants (PDAs), drop/impact could result in considerable flexure of the printed circuit board (PCB) mounted inside the cell phone housing. The mechanical stresses may cause electrical failure of the components, with typical failure mechanisms of board trace cracking, solder joint fatigue, and solder pad cracking. A standardized test needs to be developed to assess reliability of handheld components subjected to impacts. The test should facilitate high volume testing, maximize margin for safety factors, and capture the failure mechanisms in the field environment. To develop the reliability test using use conditions based reliability methodology, comprehensive characterization of the mechanical field stresses during end use conditions is particularly essential. This paper discusses complete cell phone drop characterization along with the shock test developed to test the components subjected to such drops. Novel fixtures have been designed to simulate free fall of the cell phone in specific orientations. After the complete characterization of cell phone use conditions, board level shock test has been selected to assess component reliability. Test repeatability, number of components on the test board, and layout of the components are some of the factors considered during the board level shock test development. Several parameters like screw and washer designs, torque have been studied to yield excellent test repeatability. Nonlinear Dynamic Finite Element Simulation has been performed to provide more insight into the interaction of the bending modes and its impact on the solder joint failures. This paper demonstrates the process of understanding use conditions, developing reliability tests, validating test results and driving industry standards.

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Numerical Model to Simulate the Drop Test of Printed Circuit Board (PCB)

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.423.26 ◽

2011 ◽

Vol 423 ◽

pp. 26-30

Author(s):

S. Assif ◽

M. Agouzoul ◽

A. El Hami ◽

O. Bendaou ◽

Y. Gbati

Keyword(s):

Solder Joint ◽

Printed Circuit Board ◽

Drop Test ◽

Dynamic Responses ◽

Circuit Board ◽

Joint Stress ◽

Printed Circuit ◽

Increasing Demand ◽

Improved Model ◽

Board Level

Increasing demand for smaller consumer electronic devices with multi-function capabilities has driven the packaging architectures trends for the finer-pitch interconnects, thus increasing chances of their failures. A simulation of the Board Level Drop-Test according to JEDEC (Joint Electron Device Council) is performed to evaluate the solder joint reliability under drop impact test. After good insights to the physics of the problem, the results of the numerical analysis on a simple Euler-Bernoulli beam were validated against analytical analysis. Since the simulation has to be performed on ANSYS Mechanical which is an implicit software, two methods were proposed, the acceleration-input and the displacement-input. The results are the same for both methods. Therefore, the simulation is carried on the real standard model construction of the board package level2. Then a new improved model is proposed to satisfy shape regular element and accuracy. All the models are validated to show excellent first level correlation on the dynamic responses of Printed Circuit Board, and second level correlation on solder joint stress. Then a static model useful for quick design analysis and optimization’s works is proposed and validated. Finally, plasticity behavior is introduced on the solder ball and a non-linear analysis is performed.

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