Distribution and Microstructure Analysis of Ceramic Particles in the Lead-Free Solder Matrix

The Sn-3.0Ag-0.5Cu solder alloy is a prominent candidate for the Pb-free solder, and SAC305 solder is generally employed in today’s electronic enterprise. In this study, the formation of intermetallic compounds (Cu6Sn5 and Ag3Sn) at the interface, average neighbour’s particle distance, and the morphological mosaic are examined by the addition of SiC and nickel-coated silicon carbide reinforcements within Sn-3.0Ag-0.5Cu solder. Results revealed that the addition of SiC and SiC(Ni) particles are associated with a small change to the average neighbor’s particle distance and a decrease of clustering rate to a certain limit of the Sn-3.0Ag-0.5Cu solder composites. Moreover, the development of the Cu6Sn5 and the structure of the Ag3Sn are improved with the addition of SiC and Ni coated SiC.

Particle Size and shape are critical quality and have a huge impact on the overall performance of downstream processes (such as powder treatment) and directly in uences the properties of the end products (e.g., uniformity, strength, and stability) [6,12]. Numerous off-line tools may be used to evaluate the particle size distribution (PSD) of particles produced during a crystallization technique. In-situ apparatus utilization is of speci c signi cance and Image analysis techniques can be used for evaluating size and shape data of particles dispersed in a composite [13].
Digital image processing was used to estimate the size and size distribution of round particles. The computer-based image processing technique is explored as an opportunity to provide solutions for practical measurement, identi cation, and analysis of particle distribution. Achieving similar results with a guided approach will be slow and meticulous [14]. After the particles were recognized, various methods of categorization were proposed. Chen et al. [15] have utilized wavelets for picture segmentation and the curvature of the items to distinguish circles. Larsen et al. [16] have used line tting to concentrate needlelike particles from uproarious pictures.
El Arnaout et al. [17] was managed for uneven (irregular) illumination of the image by rejecting or correcting non-focal particles by rolling background subtraction and sliding paraboloid of rotation.
Irregular illumination image was occurred due to objects out of focus, blurriness, and noise which was rejected or corrected. Sarkar et al. [18] and Zhou et al. [19] proposed object ltering methods to moderate partially distinguished objects utilizing morphological highlights and they evaluate the estimations utilizing physically clari ed particle masks.
The purpose of this investigation is to develop the SiC and SiC(Ni) reinforced Sn-3.0Ag-0.5Cu lead-free solder based composites using powder metallurgy technique to examine the microstructure, average neighbour's particle distance and morphological mosaic by the image analysis technique.

Materials And Experimental Procedures:
The base material, lead-free solder powder (SAC305) with an average particle diameter of 20-28 µm, was purchased from Cobar Europe B.V., Breda, Netherlands. The SiC provided by SIKA TECH. Switzerland with a size of 1-3 µm.
Several trials have shown that ceramic metal contact can be improved with an intermediate nickel coating. Coated ceramics production is reasonable for the PM procedure. SiC particles were coated independently with nickel via an electroless technique [20,21]. Table 1 shows the process of Ni-coating on silicon carbide particles. Operating condition: T = 85 0 C, Time (t) = 60 minutes (magnetic steering), pH = 6.5 SAC305 lead-free solder powder is mixed with three different percentages (0.5, 1.0, and 1.5wt.%) with micron-sized SiC and nickel-coated SiC by powder metallurgy route. In this examination, the SAC305 powders (average particle size of 20-28 µm) and silicon carbide (SiC) and nickel-coated silicon carbide (SiC-Ni) powders were used as the preliminary materials. As a rst strategy, the powders were mixed by the extents of SAC305-SiC and SAC305-SiC(Ni) (0.5, 1.0, and 1.5 wt%) and afterward ball milled for 1 h with ceramic balls in a ball miller.
The argon gas was used to anticipate conceivable oxidation of the new surfaces of lead-free solder particles. Each solder mixture was compressed at 200 MPa at room temperature in a cylindrical tool of 12 mm diameter to produce a cylindrical compacted sample by using a single action press. Sintering became performed at 200 0 C for 3 h under argon atmosphere. The surfaces of sintered samples were ground and polished to expel any irregularity [12].
More than 100 pictures were taken by FIB-SEM (Focus Ion Beam Scanning Electron Microscope) for inspection. The pictures have a brightening view problem, the focal point of convergence of the right is more suitable. In this way, the adaptive automatic segmentation algorithm is chosen. The particles in the segmented binary image are labeled, and the grouping of particles is examined. The Brensen calculation gave the best outcome with 31pixel window size and 85 threshold value. The particles inside the segmented binary image are labeled, and the clustering of the particles is inspected.
3. Results And Discussion:

Microstructure of solder composites:
According to FIB-SEM (Focus Beam Scanning Electron Microscope) examination in Fig. 2a, β-Sn appears directly across the entire SEM micrograph of the SAC305-SiC and SAC305-SiC(Ni)composite solder. A cross-section view of the micrograph was taken after standard metallographic polishing. Figure [7,22]. Figure 3 shows the cross-section view FIB-SEM micrograph of SAC305-SiC solder composite which contains IMCs, SiC, β-Sn, cracks, and pore along with the reinforcement.
Similar to SAC305-SiC, the matrix contains primary β-Sn particles and the IMCs (Ag 3 Sn and Cu 6 Sn 5 ) were dispersed in the matrix. Figure 4a-d demonstrates that the inclusion of a modest quantity of SiC(Ni) to SAC305 solder alloy could change the microstructure of the SAC305 solder matrix. The distribution of SiC (Ni) particles in the matrix is uniform and the better tendency to be distributed along the boundary of the β-Sn particles (Fig. 4a). Figure 4a-c additionally demonstrates that the SAC305 solder contains a lot of ne IMC particles. FIB-SEM analysis of Cu 6 Sn 5 and Ag 3 Sn IMCs shows that size and distribution have changed signi cantly between SAC305-SiC and SAC305-Si(Ni) composites. It indicates that the weight percentage of reinforcing particles is su cient to signi cantly in uence on the growth dynamics of Cu 6 Sn 5 and Ag 3 Sn in nickel-coated silicon carbide composite solder. The comparable phenomenon became also determined by Tsao [11,23], who reported that the eminent impact of TiO 2 and Al 2 O 3 particles on Pb-free solder composite solder to re ne the microstructure.
3.2 Average neighbour's particle distance: The average neighbour's particle distance, d mn , is characterized as the distance between the center of gravity between one particle and its neighbour's particles. This distance is not proportional to the mean free path between the particles and the closest neighbour distance. The distribution of SiC and SiC(Ni) particles in the SAC305 matrix are estimated to examine the impact on the matrix. Figure 5a and b demonstrate a schematic outline of estimating the average neighbour's particle distance and average neighbour's particle distance image generated by software (Cprob). If the average interparticle distance is high (distribution of the particles inside the matrix is good), the mechanical properties might be affected. Figure 6b shows the quadrat analysis of the lead-free solder composites is given as a skewness diagram of the number of SiC and SiC(Ni) particles per quadrat, N q .
Skewness diagram reveals that the overall shape of the N q distribution varies signi cantly with the degree of clustering. Indeed, an increase in the amount of reinforcement particle clusters caused the observed N q distribution to be-come less symmetric; comparison of the average neighboring particle distances of SiC According to the skewness diagram (Fig. 6b), an increase in β indicates an increase in SiC and SiC(Ni) clustering. Figure 6b shows the variation in β with the weight fraction of SiC and SiC(Ni) respectively. The skewness (β) ranges are 1.3-0.91 for SAC305/SiC and SAC305/SiC(Ni) is 1.08-0.7. The skewness range is lower for SAC305/SiC(Ni) composites than SAC305/SiC, so these outcomes are in great concurrence with the dissemination of reinforcement particles in lead-free solder. The quadrant method is a productive technique for recognizing variations in the distribution of reinforcement particles in MMCs. Furthermore, the results from the quadrat analysis can also be utilized for cluster distributions de ned by exact statistical relation. The analysis of clustered distribution is an important factor because it can improve the dispersion of reinforcement particles in the MMCs. In both reinforcements, it is small changes in skewness i.e. impact of Ni coated SiC is more than SiC.

Morphological analysis:
A mosaic picture is a segment of the plane. Each class of the segment has a mark. Such a segment is produced, speci cally, when utilizing object-oriented image coding. The image is portioned into homogeneous zones. The present examination presents an interpolation method for mosaic pictures. The examination of the size appropriation of the cells from the mosaic can demonstrate the clustering of the items. The segmented binary picture was investigated. Another technique is the examination of the morphological mosaic. Here rises the issue of the characteristic point, and this approach overlooks the form of the object. With a constant dilatation of the objects, the tessellation may be made, which is delicate to the size and the state of the object. This technique is the morphological mosaic technique. The investigation of the size carrying of the cell from the mosaic can show the clustering of the objects.
FIB-SEM micrographs are taken from the polished samples of the inspected tests of SAC305 + SiC/SiC(Ni). SiC particles in the blue form are visible in the micrograph. In Fig. 7a and b, the distribution of the SiC particles are in cells. It can be seen as larger and smaller cells in the mosaic structure. In this manner, the size (region) dissemination of the cells is considered. Therefore, the size (area) distribution of the cells is studied. A larger effect can be seen in the SAC305/SiC(Ni) solder composite (Fig. 8a). Figure 8a shows the average cell area of both composites and the cell area of Ni coated SiC composite is increased at different weight fractions i.e. particles are uniformly distributed. Figure 8b shows the skewness variation of both composites and SiC(Ni) reinforced composite skewness is much lower than SiC composites i.e. Ni is very effective in the distribution of the particles in the SAC305 solder matrix.

Conclusions
This current study investigates the impact of small quantity SiC and nickel-coated SiC microparticles addition on microstructure, average neighbour's particle distance, and morphological mosaic behaviors of Pb-free Sn-3.0Ag-0.5Cu alloy.  Schematic diagram of reinforcement and matrix powder (modi ed): (a) before milling (zero-hour milling) and (b) after milling (homogeneous distribution). Adapted from Ref. [5].