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

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

Journal of the Microelectronics and Packaging Society ◽

10.6117/kmeps.2015.22.1.069 ◽

2015 ◽

Vol 22 (1) ◽

pp. 69-74

Author(s):

Han Choi ◽

So-Jeong Lee ◽

Yong-Ho Ko ◽

Jung-Hwan Bang ◽

Jun-Ki Kim

Keyword(s):

Solder Joint ◽

Solder Paste ◽

Sac305 Solder ◽

Joint Properties ◽

Board Level

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The Effect of Multiple Reflow Times on Lead-Free Solder Joint Microstructure

2003 International Electronic Packaging Technical Conference and Exhibition, Volume 2 ◽

10.1115/ipack2003-35150 ◽

2003 ◽

Author(s):

Sami T. Nurmi ◽

Janne J. Sundelin ◽

Eero O. Ristolainen ◽

Toivo K. Lepisto¨

Keyword(s):

Solder Joint ◽

Solder Joints ◽

Lead Free ◽

Lead Free Solder ◽

Solder Paste ◽

Snagcu Solder ◽

Silver Copper ◽

Free Solder ◽

Tin Silver Copper ◽

Lead Free Solders

As environmental issues are raising more interest and are becoming crucial factors in all parts of the world, more and more environmental-friendly electronics products are emerging. Usually this means the introduction of products with lead-free solders. However, the reliability of lead-free solders is still a serious concern despite the vast research done in this field. This paper will describe the interconnect reliability of three kinds of solder joints respectively prepared with lead-free solder paste and lead-free PBGA components, lead-free solder paste and tin-lead-silver PBGA components, and tin-lead solder paste and tin-lead-silver PBGA components. Lead-free and tin-lead solders were composed of eutectic tin-silver-copper and tin-lead, respectively. In addition, the study also presents the effect of multiple reflow times. The study focuses on the microstructures of different assemblies. The particular interest is on the assemblies soldered with lead-free solder paste and tin-lead-silver PBGA components, since the SnPbAg solder on the bumps of the PBGA components were exposed to the reflow profile meant for the lead-free SnAgCu solder. Thus, these SnPbAg solder bumps were in the molten state almost twice as long as the rest of the solders. This had a notable effect on the reliability of these solder joints as we will be showing later in this paper. The test boards were temperature-cycled for 2500 cycles between −40 and +125°C (a 30-minute cycle). PBGA solder joint failures were monitored with a real time monitoring system. Optical and scanning electron microscopy was used to inspect the broken solder joints and their microstructure. The results of tests indicate that the number of reflow times can significantly affect the lifetime of PBGA solder joints. The most notable changes can be seen in the solder joints made with tin-lead-silver PBGA components and tin-silver-copper solder paste soldered with a lead-free reflow profile. The general trend was that the reliability of the solder joints increased in proportion to the number of reflow times. Mainly two factors are believed to have the major effect on the reliability of PBGA solder joints, voids, and microstructural changes in solder.

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Investigation of the Lead-free Solder Joint Shear Performance

Journal of Microelectronics and Electronic Packaging ◽

10.4071/1551-4897-4.2.72 ◽

2007 ◽

Vol 4 (2) ◽

pp. 72-77 ◽

Cited By ~ 3

Author(s):

James Webster ◽

Jianbiao Pan ◽

Brian J. Toleno

Keyword(s):

Shear Strength ◽

Solder Joint ◽

Thermal Shock ◽

Liquidus Temperature ◽

Solder Joints ◽

Sac305 Solder ◽

Joint Shear Strength ◽

Snagcu Solder ◽

Shear Performance ◽

Joint Shear

Reflow profile has significant impact on solder joint performance because it influences wetting and microstructure of the solder joint. The purpose of this study is to investigate the effects of reflow profile and thermal shock on the shear performance of eutectic SnPb (SnPb) and Sn3.0Ag0.5Cu (SAC305) solder joints. Test boards were assembled with four different sized surface mount chip resistors (1206, 0805, 0603 and 0402). Nine reflow profiles for SAC 305 and nine reflow profiles for SnPb were developed with three levels of peak temperature (12°C, 22°C, and 32°C above solder liquidus temperature, or 230°C, 240°C, and 250°C for SAC 305; and 195°C, 205°C, and 215°C for SnPb) and three levels of time above solder liquidus temperature (30 sec., 60 sec., and 90 sec.). Half of the test vehicles were then subjected to air-to-air thermal shock conditioning from −40 to 125°C. The shear force data were analyzed using the Analysis of Variance (ANOVA). The fracture surfaces were studied using a Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). It was found that thermal shock degraded both SnPb and SnAgCu joints shear strength, and that the effect of thermal shock on solder joint shear strength is much more significant than that of reflow profile. The SnAgCu solder joints have weaker shear strength than the SnPb solders. The SnAgCu solder joint after thermal shock retains more of its shear strength than that of SnPb for small components and vice versa for larger components.

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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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