Low Melting Temperature Solder Materials for Use in Flexible Microelectronic Packaging Applications

The increasing application of heat-sensitive microelectronic components such as a multitude of transistors, polymer-based microchips, and so on, and flexible polymer substrates including polyethylene terephthalate (PET) and polyimide (PI), among others, for use in wearable devices has led to the development of more advanced, low melting temperature solders (<150°C) for interconnecting components in various applications. However, the current low melting temperature solders face several key challenges, which include more intermetallic compound formation (thus become more brittle), cost issues according to the addition of supplementary elements to decrease the melting point temperature, an increase in the possibility of thermal or popcorn cracking (reliability problems), and so on. Furthermore, the low melting temperature solders are still required to possess rapid electronic/electrical transport ability (high electrical conductivity and current density) and accompany strong mechanical strength sustaining the heavy-uploaded microelectronic devices on the plastic substrates, which are at least those of the conventional melting temperature solders (180–230°C). Thus, the pursuit of more advanced low melting temperature solders for interconnections is timely. This review is devoted to the research on three methods to improve the current properties (i.e., electrical and thermomechanical properties) of low melting temperature solders: (i) doping with a small amount of certain additives, (ii) alloying with a large amount of certain additives, and (iii) reinforcing with metal, carbon, or ceramic materials. In this review, we also summarize the overall recent progress in low melting temperature solders and present a critical overview of the basis of microscopic analysis with regard to grain size and solid solutions, electrical conductivity by supplementation with conductive additives, thermal behavior (melting point and melting range) according to surface oxidation and intermetallic compound formation, and various mechanical properties

TỔNG HỢP NANO BẠC BẰNG PHƯƠNG PHÁP NỔ

The technology of wire explosion has been used to produce nanopowders [1, 4, 5, 8, 9]. A new concept was proposed to produce nanosized powder, which is wire explosion in liquid media. We have exploded the Ag wires with 0.1 to 0.3 mm diameter, in the de-ionized water. Electrical energy of 1.1 kJ was stored in a 10-uF capacitor and released to the wires through a triggered spark gap switch. As a consequence, there were no micrometer size particles in the powder, which is attributed to the complete vaporization of the wire. It is considered that the wire explosion in liquid medium meets three conditions to form smaller particles, namely, higher energy deposition in the wire, sufficient expansion volume, and quick cooling of the particles

Laser deposition additive manufacturing of 17-4PH stainless steel on Ti-6Al-4V using V interlayer

For the first time, additive manufacturing was used to obtain a strong joint (bonding strength >200 MPa) between stainless steel and Ti-6Al-4V using a V interlayer. The V interlayer applied via solid-state joining prevented the formation of brittle intermetallic phases more effectively than a V interlayer deposited by a liquid-state process. The microstructure and strength of the joint interface depended on the laser power and scan speed. The joint strength decreased with increasing annealing time, especially after 4 and 24 h, demonstrating the presence of the Fe-V-Cr σ-phase

Comparison of Nano-Mechanical Behavior between Selective Laser Melted SKD61 and H13 Tool Steels

Using nanoindentation under various strain rates, the mechanical properties of a laser powder bed fusion (PBF) SKD61 at the 800 mm/s scan speed were investigated and compared to PBF H13. No obvious pile-up due to the ratio of the residual depth (hf) and the maximum depth (hmax) being lower than 0.7 and no cracking were observed on any of the indenter surfaces. The nanoindentation strain-rate sensitivity (m) of PBF SKD61 was found to be 0.034, with hardness increasing from 8.65 GPa to 9.93 GPa as the strain rate increased between 0.002 s&#8722;1 and 0.1 s&#8722;1. At the same scan speed, the m value of PBF H13 (m = 0.028) was lower than that of PBF SKD61, indicating that the mechanical behavior of PBF SKD61 was more critically affected by the strain rate compared to PBF H13. PBF processing for SKD61 therefore shows higher potential for advanced tool design than for H13

Densifying method in additive manufacturing process of H13 tool steel: Laser re-melting

AISIH13 tool steel structures were fabricated by selective laser melting which is one of the metal additive manufacturing process. Scanning speed of laser was controlled in the ranging of 100-1000 mm/s to optimize the process parameter to fabricate the highly densified structure. Laser power, hatch space and layer thickness were fixed at 90 W, 80 urn and 25 urn. Under 200 mm/s, spherical shape pores were observed and irregular shape pores were observed in over 400 mm/s samples. Residual pores were not easily removed by changing laser scanning speed alone and laser re-melting technique was applied to solve the pore problem. Each layers were exposed twice to laser with various scanning speed before re-coating the powder for next layer. Spherical shape pores were observed from all of the specimen exposed under 200 mm/s irrespective of another exposed laser speed. While re-melting over scanning speed of 800 mm/s did not showed effect on the densification, the combination of first scanning speed (400 mm/s) and second scanning speed (600 mm/s) showed the significant reduction of pores. Copyright ?? 2018 by Nanyang Technological Universit

DUAL SPEED LASER RE-MELTING FOR HIGH DENSIFICATION IN H13 TOOL STEEL METAL 3D PRINTING

The densification behavior of H13 tool steel powder by dual speed laser scanning strategy have been characterized for selective laser melting process, one of powder bed fusion based metal 3d printing. Under limited given laser power, the laser re-melting increases the relative density and hardness of H13 tool steel with closing pores. The single melt-pool analysis shows that the pores are located on top area of melt pool when the scanning speed is over 400 mm/s while the low scanning speed of 200 mm/s generates pores beneath the melt pool in the form of keyhole mode with the high energy input from the laser. With the second laser scanning, the pores on top area of melt pools are efficiently closed with proper dual combination of scan speed. However pores located beneath the melt pools could not be removed by second laser scanning. When each layer of 3d printing are re-melted, the relative density and hardness are improved for most dual combination of scanning. Among the scan speed combination, the 600 mm/s by 400 mm/s leads to the highest relative density, 99.94 % with hardness of 53.5 HRC. This densification characterization with H13 tool steel laser re-melting can be efficiently applied for tool steel component manufacturing via metal 3d printing