Effects of metallic nanoparticle doped flux on the interfacial intermetallic compounds between lead-free solder ball and copper substrate

doi:10.1016/j.matchar.2014.10.002

Materials Characterization

Volume 97, November 2014, Pages 199-209

https://doi.org/10.1016/j.matchar.2014.10.002 Get rights and content

Highlights

•
A novel nanodoped flux method has been developed to control the growth of IMCs.
•
Ni doped flux improves the wettability, but Co, Mo and Ti deteriorate it.
•
Ni and Co doped flux gives planer IMC morphology through in-situ alloying effect.
•
0.1 wt.% Ni and Co addition into flux gives the lowest interfacial IMC thickness.
•
Mo and Ti doped flux does not have any influence at the interfacial reaction.

Abstract

Lead free solders currently in use are prone to develop thick interfacial intermetallic compound layers with rough morphology which are detrimental to the long term solder joint reliability. A novel method has been developed to control the morphology and growth of intermetallic compound layers between lead-free Sn–3.0Ag–0.5Cu solder ball and copper substrate by doping a water soluble flux with metallic nanoparticles. Four types of metallic nanoparticles (nickel, cobalt, molybdenum and titanium) were used to investigate their effects on the wetting behavior and interfacial microstructural evaluations after reflow. Nanoparticles were dispersed manually with a water soluble flux and the resulting nanoparticle doped flux was placed on copper substrate. Lead-free Sn–3.0Ag–0.5Cu solder balls of diameter 0.45 mm were placed on top of the flux and were reflowed at a peak temperature of 240 °C for 45 s. Angle of contact, wetting area and interfacial microstructure were studied by optical microscopy, field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. It was observed that the angle of contact increased and wetting area decreased with the addition of cobalt, molybdenum and titanium nanoparticles to flux. On the other hand, wettability improved with the addition of nickel nanoparticles. Cross-sectional micrographs revealed that both nickel and cobalt nanoparticle doping transformed the morphology of Cu₆Sn₅ from a typical scallop type to a planer one and reduced the intermetallic compound thickness under optimum condition. These effects were suggested to be related to in-situ interfacial alloying at the interface during reflow. The minimum amount of nanoparticles required to produce the planer morphology was found to be 0.1 wt.% for both nickel and cobalt. Molybdenum and titanium nanoparticles neither appear to undergo alloying during reflow nor have any influence at the solder/substrate interfacial reaction. Thus, doping of flux with appropriate metallic nanoparticles can be successfully used to control the morphology and growth of intermetallic compound layers at the solder/substrate interface which is expected to lead to better reliability of electronic devices.

Introduction

Restrictions on the use of lead (Pb) based solder alloys in microelectronic assemblies because of the inherent toxicity of Pb pave the path to develop various tin based solder alloys. Among the lead-free solders, the ternary tin based tin–silver–copper (SAC) solder alloys are popular at present to replace the eutectic Sn–Pb solder due to their relatively low melting temperature (~ 217 °C–220 °C) compared to other Pb-free Sn based solder alloys, enhanced strength, improved creep and thermal fatigue characteristics and good compatibility with device components [1], [2].

Intermetallic compounds (IMCs) formed between solder and substrate play a vital role in determining the long term reliability of microelectronic packages. A thinner, planer and continuous intermetallic compound (IMC) layer is essential as it ameliorates a strong bonding at the interface. However, excessive IMC layer can degrade the mechanical properties of solder joints leading to a catastrophic failure [3], [4], [5], [6]. Tin based lead free solders developed so far are known to lead to the formation of thick interfacial intermetallic compound layers with rough morphologies. Thus, controlling the morphology and growth of interfacial IMC is important to ensure solder joint reliability.

Alloy addition to bulk of solder by conventional metallurgical processing is one of the ways of controlling the morphology and growth of IMC layer [4], [5], [7], [8], [9]. Reinforcement of lead-free solder alloys through the addition of nanoparticles leading to a nano-composite solder is another method to control the morphology and growth of IMC at the solder/substrate interface [10], [11], [12]. Reinforcement of lead-free solder alloys with metallic nanoparticles is being extensively investigated as these can control the IMC morphology and thickness through alloying effect [13], [14], [15], [16] or through pinning effect by adsorbing preferentially at solder/substrate interface [11] for the improvement of solder joint reliability.

Solder paste mixing method is a simple and direct approach to prepare nano-composite solder. So far, the influence of nanoparticles on the morphology and growth of interfacial IMCs has been studied by mixing them with solder paste. Recent studies suggest that doping various types of metallic nanoparticles such as Ni [13], Co [14], Mo [11] and Zn [15], [16] with SAC solder paste has a definite influence on the morphology and growth of interfacial IMCs. Thus, nanoparticle reinforcement through solder paste mixing can be considered as a suitable way to improve the solder joint reliability in surface mount technology (SMT).

In ball grid array (BGA) flip chip assemblies, a common method of preparing solder joint is the flux dipping method [17], [18], [19], [20]. In the flux dipping method, a commercially available flux is placed on top of the solder pads of printed circuit board (PCB). Then, the solder balls are placed on top of the flux and reflowed to prepare the BGA interconnections. It was reported by Wang et al. [17] that the flux dipping method showed better drop impact reliability of BGA assemblies due to having finer IMC grains at SAC105/Cu interface compared with conventional paste printing method. Although the flux dipping technique may yield a comparatively thinner IMC layer after reflow, a thick and rough interfacial IMC formation at the SAC solder/substrate interface compared with lead based counterparts still remains a concern for the long term solder joint reliability. Until now, no research work has been done investigating an easy way to engineer the interfacial IMCs in the flux dipped method.

In the present study, a novel nanodoped flux method has been developed by mixing metallic nanoparticles with a commercially available water soluble flux to control the morphology and growth of interfacial IMCs in the BGA and flip chip assemblies [21]. This paper investigates the effects of doping a water soluble flux with Ni, Co, Mo and Ti nanoparticles on the morphology and growth of interfacial intermetallic compounds (IMCs) between lead-free Sn–3.0Ag–0.5Cu solder and Cu substrate. Solder joints prepared with nanodoped flux are also investigated for comparison.

Section snippets

Experimental Procedures

Commercially available nickel, cobalt, molybdenum and titanium nanoparticles (Accumet Materials, Co., USA) were used in this study. The crystallite phases of each type of metallic nanoparticles were investigated by X-ray diffractometer (XRD-PANalytical). Field emission scanning electron microscopy (FESEM) was conducted to determine the nanoparticle size and morphology using an in-lens detector of 1 kV EHT voltage. For FESEM sample preparation, the nanoparticles were dispersed ultrasonically

Characterization of As-received Metallic Nanoparticles

Fig. 2 shows the X-ray diffraction patterns for the as-received metallic nanoparticles used in this study. In Fig. 2a, three dominant peaks at 44.69°, 52.05° and 76.51° belong to (111), (002) and (022) planes of metallic Ni. In addition, two evidential peaks of NiO appear at 37.37° and 62.96° represent (111) and (022) crystal planes. In Fig. 2b, three sharp peaks seen at 44.13°, 51.40° and 75.79° represent (111), (002) and (022) crystal planes of Co. Moreover, a single peak of Co₃O₄ appears at

Incorporation of Nanoparticles into Solder

Based on the results described above, the metallic nanoparticles used in the present study can be divided into two groups. The first group includes Ni and Co. These nanoparticles are seen to be incorporated into the solder. They enter into the interfacial Cu₆Sn₅ IMC layer. They are also found to be incorporated into the Cu₆Sn₅ particles situated in the matrix near the interface. It has been explained in earlier studies that nanoparticles of Ni [13], Co [14] and Zn [15], [16] undergo reactive

Conclusions

From this work, the following conclusions can be drawn:

01.
Doping of flux with metallic nanoparticles has been successful to impart their influence at the solder/substrate interface.
02.
Doping Ni nanoparticle to flux improves the wettability of the solder joint, while Co, Mo and Ti nanoparticles deteriorate the wettability of the solder joint.
03.
Interfacial morphology has been changed from a scallop to a planer type with Ni and Co addition through an in-situ alloying effect. This morphological change is

Acknowledgments

The authors acknowledge the financial support of the High Impact Research grant (UM.C/HIR/MOHE/ENG/26, Grant No. D000026-16001) and the University of Malaya Research grant (UMRG, Grant No. RP021-2012D).

References (41)

J.-M. Kim et al.
Effects of surface finishes and loading speeds on shear strength of Sn–3.0Ag–0.5Cu solder joints
Microelectron. Eng.
(2012)
Y. Zhang et al.
Low-temperature creep of SnPb and SnAgCu solder alloys and reliability prediction in electronic packaging modules
Scr. Mater.
(2013)
F. Sun et al.
Fracture morphology and mechanism of IMC in low-Ag SAC solder/UBM(Ni(P)–Au) for WLCSP
Microelectron. Reliab.
(2008)
C. Yang et al.
Impact of Ni concentration on the intermetallic compound formation and brittle fracture strength of Sn–Cu–Ni (SCN) lead-free solder joints
Microelectron. Reliab.
(2014)
A. Fawzy
Effect of Zn addition, strain rate and deformation temperature on the tensile properties of Sn–3.3 wt.% Ag solder alloy
Mater. Charact.
(2007)
J. Hu et al.
Depressing effect of 0.1 wt.% Cr addition into Sn–9Zn solder alloy on the intermetallic growth with Cu substrate during isothermal aging
Mater. Charact.
(2010)
U. Böyük et al.
Effect of solidification parameters on the microstructure of Sn–3.7Ag–0.9Zn solder
Mater. Charact.
(2010)
Y. Tang et al.
Influence of TiO₂ nanoparticles on IMC growth in Sn–3.0Ag–0.5Cu–xTiO₂ solder joints in reflow process
J. Alloys Compd.
(2013)
A.S.M.A. Haseeb et al.
Stability of Molybdenum nanoparticles in Sn–3.8Ag–0.7Cu solder during multiple reflow and their influence on interfacial intermetallic compounds
Mater. Charact.
(2012)
A.K. Gain et al.
The influence of addition of Al nano-particles on the microstructure and shear strength of eutectic Sn–Ag–Cu solder on Au/Ni metalized Cu pads
J. Alloys Compd.
(2010)

S.L. Tay et al.

Influence of Ni nanoparticles on the morphology and growth of interfacial compounds between Sn–3.8Ag–0.7Cu lead-free solder and copper substrate

Intermetallics

(2013)

A.S.M.A. Haseeb et al.

Effects of Co nanoparticle addition to Sn–3.8Ag–0.7Cu solder on interfacial structure after reflow and ageing

Intermetallics

(2011)

A.S.M.A. Haseeb et al.

In-situ alloying of Sn–3.5Ag solder during reflow through Zn nanoparticle addition and its effects on interfacial intermetallic layers

Intermetallics

(2014)

B. Wang et al.

Drop impact reliability of Sn–1.0Ag–0.5Cu BGA interconnects with different mounting methods

Microelectron. Reliab.

(2012)

T. Laurila et al.

Interfacial reactions between lead-free solders and common base materials

Mater. Sci. Eng. R

(2005)

F. Gao et al.

Effects of Co and Ni addition on reactive diffusion between Sn–3.5Ag solder and Cu during soldering and annealing

Mater. Sci. Eng. A

(2006)

M. Amagai

A study of nanoparticles in Sn–Ag based lead free solders

Microelectron. Reliab.

(2008)

L. Vitos et al.

The surface energy of metals

Surf. Sci.

(1998)

C. Yu et al.

First-principles investigation of the structural and electronic properties of Cu_6 − xNi_xSn₅ (x = 0, 1, 2) intermetallic compounds

Intermetallics

(2007)

G. Balasubramanian et al.

Shear viscosity enhancement in water–nanoparticle suspensions

Phys. Lett. A

(2012)

Cited by (46)

Interfacial reaction and shear strength of ultrasonically-assisted Sn-Ag-Cu solder joint using composite flux
2021, Journal of Manufacturing Processes
Citation Excerpt :
However, comparing to the Sn-Pb solders, the SAC solders still have a lot of problems, for instance, the wettability of SAC solder was worse than that of Sn-Pb solders [8]. More importantly, the formation of interfacial intermetallic compounds (IMCs) was detrimental to the reliability of solder joints [9,10], which challenged the long-term reliability of SAC solder joints, resulting in failure to meet the strict requirement of the miniaturization of solder joints. Hence, it was no surprise that the improvement on mechanical behaviours of solder joints by reducing the thickness of interfacial IMCs have attracted considerable focus.
Cu modified carbon nanotubes (Cu-CNTs) doped flux were prepared in this paper, the influence of the composite flux on the evolution of microstructure and shear strength of Sn-3.0Ag-0.5Cu (SAC305) solder joints were investigated, the ultrasonic vibration (USV) was applied for the solder joint during reflowing. Experiments were designed to modify the CNTs with Cu nanoparticles through electroless modification process. Transmission electron microscopy (TEM) was utilized to obtain the graph of modified CNTs. Using X-ray photoelectron spectroscopy (XPS) spectra to prove that the CNTs were successfully modified with Cu nanoparticles. Compared with the solder joint without USV, the application of USV on the solder joint would alter the morphologies of interfacial IMC layer and grains, reduce the IMC thickness and grain size by 16.6 % and 65.6 %, respectively. Reflow process was implemented to evaluate the microstructure evolution and interfacial reaction of SAC305 solder joint with different content of Cu-CNTs doped flux with USV. It was found that the presence of Cu-CNTs could reduce the thickness and grain size of interfacial intermetallic compound (IMC) within solder joint by 3.1 % and 5.25 %, respectively. After addition of the Cu-CNTs in the flux, the thickening of IMC layer and the coarsen of interfacial IMC grain were suppressed, the optimal inhibition effect was gained when the content of Cu-CNTs was 0.1 wt.%. The shear test was conducted for the Cu/SAC305/Cu solder joint with flux containing Cu-CNTs under different soldering condition, the results indicated that as the content of the Cu-CNTs in the flux increased, the shear strength was significantly enhanced by up to 16.8 %. Furthermore, the application of USV could enhance the shear strength by up to 14.2 % as well, The fracture type of solder joints without USV treatment also changed from ductile-brittle mixed type to ductile type as the content of Cu-CNTs in the flux increased. While, the fracture type of all the solder joints with USV treatment was ductile type.
Materials modification of the lead-free solders incorporated with micro/nano-sized particles: A review
2021, Materials and Design
Citation Excerpt :
Meanwhile, it was clear in Fig. 15 that Ni nanoparticles addition gave rise to the growth of (Cu, Ni)6Sn5 IMC, and doping Ni nanoparticles promoted the growth of (Cu, Ni)6Sn5 IMC grains and impeded that of Cu3Sn IMC grains. Sujan et al. [50], who found a novel method that Ni, Co, Mo and Ti four types of metallic nanoparticles were respectively introduced into flux via manual mixing, investigated the effects on the wettability, the microstructure and IMC layers growth that between the solder ball and Cu substrate after reflowing. As Fig. 16 demonstrated that the contact angle put up and the wetting area cut down with the increasing amount of nano-sized Co, Mo and Ti particles added to the flux while Ni nanoparticles showed the reverse trend.
As to promote the performance of the solder joints applied to electronics industry, the researchers take advantage of micro/nano-sized particles or another element coated on nanoparticles to be incorporated into the solder paste or flux and investigate their microstructure and properties. Based on refinement strengthening and dispersion strengthening theory, it was reported that introducing nanoparticles into the solder could significantly refine the matrix of the solder, improve the wetting ability and strengthen the mechanical performance of the solder joints. In this review, the influence and mechanism of varying sizes and contents of the metallic particles, intermetallic compound particles, metal oxide particles and carbon nanoparticles on the structure and performance of the solder is comprehensively summed up. Subsequently, the influence of nanoparticles on the melting temperature, wettability, microstructure, mechanical evolution, creep behaviors, electromigration properties and reliability of the solder has been summarized. Furthermore, the effect of micro-sized particles addition to solder alloy in 3D packaging also has been sketched out. Finally, the shortcomings of nanoparticle reinforced lead-free solder are put forward in order to provide a theoretical basis for the future development of particle-reinforced solder with excellent properties.
Effects of Ni modified MWCNTs on the microstructural evolution and shear strength of Sn-3.0Ag-0.5Cu composite solder joints
2020, Materials Characterization
A composite solder was prepared by adding different amount Ni modified multi-walled carbon nanotubes (MWCNTs) into the Sn-3.0Ag-0.5Cu (SAC305) solder. Experiments were conducted to investigate the thermal behavior, mechanical properties of composite solder alloys, shear fracture behavior of solder joints were evaluated as well. The modification process was carried out on the MWCNTs using electroless modification method to synthesis the Ni modified carbon nanotubes (Ni-CNTs), which was manually mixed into SAC305 solder powder with different amount. The melting point of the composite solder alloys was slightly increased with the increment of the amount of Ni-CNTs. The nanoindentation test results confirmed that the hardness and modulus of composite solder alloys were enhanced after the addition of Ni-CNTs. The aging experiment was implemented for the joints and the results indicated that the Ni-CNTs could effectively inhibit the growth of IMC layer as an additive in SAC305 solder. The shear strength of SAC305-xNi-CNTs/Cu (x = 0, 0.1 and 0.2 wt.%) joints was reinforced with the increment of Ni-CNTs amount. Furthermore, the SAC305-0Ni-CNTs/Cu and SAC305-0.1Ni-CNTs/Cu solder joints were broken partially between the solder and IMC, mostly between the solder matrix, and SAC305-0.2Ni-CNTs/Cu solder joint was broken completely inside solder matrix. It was suggested that the fracture mode of the solder joints changed from mix fracture mode to ductile fracture mode as the amount of Ni-CNTs increased.
Enhancement of hardness of bulk solder by doping Cu nanoparticles at the interface of Sn/Cu solder joint
2019, Microelectronic Engineering
Citation Excerpt :
Mohd Salleh et al. [6] have utilized TiO2 nanoparticles to suppress the IMC growth kinetics during multiple reflow and improve the shear strength of the formed solder joint. Co, Mo, Ni and Ti nanoparticles have been separately doped into the organic flux and SAC 305 and Cu joints were formed using the same doped flux in the works of Sujan et al. [7]. Another work by Haseeb et al. [8] utilizes Zn nanoparticles doped flux to form joint between Sn-3.5Ag solder and Cu substrate.
In this study, Cu NPs prepared by chemical reduction method,were doped into flux at weight proportions (0, 0.2, 0.5, 1 and 2 wt.%) and then reflow soldering was performed for the pure Sn solder (initial diameter = 1400 μm) with Cu substrate at 250 °C for 120 s. The presence of Cu nanoparticles (NPs) in soldering flux was observed to enhance the spreading of solder on Cu substrate. Solder with larger base spread area, characterized with faster diffusion of Cu from substrate attained quicker supersaturation during reflow and larger precipitation of primary Cu₆Sn₅ intermetallics (IMCs) upon air cooling. The solders containing greater area proportion of primary IMCs are characterized with enhanced effective elastic modulus. Experimentally, the solders prepared with Cu nanoparticles composed flux,were characterized with the increase in Vicker's microhardness. Solder processed with flux containing 2 wt.% Cu nanoparticles possessed Vicker's hardness of 18.6 HV, whereas solder prepared with undoped flux only had hardness of 13.8 HV. Numerical computation of the Cu diffusion and the elasticity have been done using finite element method.
Geometrical effects on growth kinetics of interfacial intermetallic compounds in Sn/Cu joints reflowed with Cu nanoparticles doped flux
2019, Thin Solid Films
In this study, Cu nanoparticles prepared by chemical reduction method, were doped into flux (0–2 wt%) and disseminated to the pure Sn solder ball at 250. The enhanced spreading rate due to use of nanoparticles, increased the base diameter (W) and decreased the height (H) of the solder at constant volume. The finite element analysis for Cu concentration, temperature and velocity; in relation to the magnitudes of W and H show that larger W is responsible for enhancement of supersaturation and radial thermal gradient, whereas smaller H is responsible for reduction in flow velocity. The growth kinetics of interfacial Cu ₆Sn ₅ film during isothermal reflow is proportional to W ^2/3 during isothermal reflow whereas linearly dependent on H during air cooling. As the ripening at isothermal stage and precipitation at cooling stage contribute to the gross growth behavior of Cu ₆Sn ₅ intermetallic compounds layer growth, the combined geometrical effect of base diameter and height of the solder specimen renders solder corresponding to flux with 2.0 wt% nanoparticles to have the overall thickest intermetallics.
Investigation on nano-reinforced solder paste after reflow soldering part 1: Effects of nano-reinforced solder paste on melting, hardness, spreading rate, and wetting quality
2018, Microelectronics Reliability
In this study, the effects of three distinctive contents of metal oxide [Iron Nickel Oxide (Fe₂NiO₄), Iron Oxide (Fe₂O₃), Nickel Oxide (NiO), and Indium Tin Oxide (ITO)] and carbon nanostructure [diamond (C)]-reinforced solder paste on melting behavior, hardness, spreading rate, and wetting angle after reflow soldering were differentiated. Each nanoparticle was mechanically mixed with SAC 305 solder paste to produce homogeneous nanocomposite solder alloys. Based on the results, the addition of nanoparticles slightly increased the melting point; except for the SAC 305-ITO and SAC 305-Diamond composite solder pastes. The SAC 305-ITO composite solder showed negligible effects, but the SAC 305-Diamond composite solder reduced the melting point. The SAC 305-Diamond composite solder exhibited a very high increment in solder hardness compared with other nanocomposite solder pastes. Reinforcement of 0.5 wt% diamond nanoparticles increased solder viscosity higher than other metal oxide nanoparticles. The flow rate of SAC 305-Diamond molten solder on Cu substrate decreased upon the nanoparticle addition during reflow soldering. The reduction in the spreading caused the enlargement in the wetting angle of solder paste. However, very low percentage of carbon nanostructure addition into molten solder alloys reduced the melting point and increased solder hardness with tolerable spreading rate and wetting quality, which enhanced solder reliability after reflow.

View all citing articles on Scopus

¹: Country of origin: Bangladesh.

²: Country of origin: Malaysia.

View full text

Effects of metallic nanoparticle doped flux on the interfacial intermetallic compounds between lead-free solder ball and copper substrate

Highlights

Abstract

Introduction

Section snippets

Experimental Procedures

Characterization of As-received Metallic Nanoparticles

Incorporation of Nanoparticles into Solder

Conclusions

Acknowledgments

Microelectron. Eng.

Scr. Mater.

Microelectron. Reliab.

Microelectron. Reliab.

Mater. Charact.

Mater. Charact.

Mater. Charact.

J. Alloys Compd.

Mater. Charact.

J. Alloys Compd.

Intermetallics

Intermetallics

Intermetallics

Microelectron. Reliab.

Mater. Sci. Eng. R

Mater. Sci. Eng. A

Microelectron. Reliab.

Surf. Sci.

Intermetallics

Phys. Lett. A