Mi Jin Kim, Y. (Norman) Zhou and Jae Pil Jung
This paper seeks to decrease the soldering temperature of capacitors using Sn‐Bi plated Sn‐3.5 wt%Ag solder.
Abstract
Purpose
This paper seeks to decrease the soldering temperature of capacitors using Sn‐Bi plated Sn‐3.5 wt%Ag solder.
Design/methodology/approach
Sn‐Bi layers were electroplated on Sn‐3.5 wt%Ag solder. As soldering examples, type 1608 capacitors electroplated with Sn, and printed circuit boards (PCBs) with a surface coating of electroless‐plated Ni/Au, were selected. Sn‐3.5Ag foil coupons plated with Sn‐95.7 wt%Bi were inserted as solder between the capacitors and the lands on the PCBs. The samples were reflowed at 220°C, which is below the normal reflow temperatures of around 240 ∼ 250°C used with Pb‐free solders. During heating, Bi in the plated layer diffuses into the Sn‐3.5Ag core solder resulting in a transient decrease in soldering temperature based on the concept of transient liquid phase bonding.
Findings
The joints made with the Sn‐95.7%Bi plated Sn‐3.5Ag solder at 220°C showed good appearance, and evidence of significant Bi segregation was absent in the microstructure. The shear strengths of the capacitor joints bonded with Sn‐95.7%Bi plated Sn‐3.5%Ag solder were approximately 5,000‐6,000 gf. After 1,000 thermal cycles between −40 and +125°C, the shear strengths of the joints decreased approximately 5‐10 percent from the strengths in the as‐reflowed state for all plated solders. This confirmed that the soldered joints were stable and not significantly degraded by thermal cycles.
Originality/value
Reduced temperature soldering using Sn‐Bi plated Sn‐3.5%Ag solder was applied to attach capacitors to PCBs. In a production application, the foil coupons could be replaced by pre‐solder on the PCB pads.
Details
Keywords
Joon Kwon Moon, Y. Zhou and Jae Pil Jung
To investigate fluxless plasma ball bumping and effect of under bump metallization (UBM) thickness on joint properties using lead‐free solders.
Abstract
Purpose
To investigate fluxless plasma ball bumping and effect of under bump metallization (UBM) thickness on joint properties using lead‐free solders.
Design/methodology/approach
A fluxless soldering process was investigated in this study using Ar‐10 percent H2 plasma reflow. Balls made from two lead‐free solders (Sn‐3.5 weight percent Ag and Sn‐3.5 weight percent Ag‐0.7 weight percent Cu) were reflowed and, also Sn‐37 weight percent Pb as a reference. In particular, the effects of the UBM thickness on the interfacial metallurgical bonding and joint strength were studied. The UBM (Au/Cu/Ni/Al layers) thicknesses were 20 nm/0.3 μm/0.4 μm/0.4 μm and 20 nm/4 μm/4 μm/0.4 μm, respectively.
Findings
The experimental results showed that in the case of a thin UBM the shear strengths of the soldered joints were relatively low (about 19‐27 MPa) due to cracks observed along the bond interfaces. The thick UBM improved joint strength to 32‐42 MPa as the consumption of the Cu and Ni layers by reaction with the solder was reduced and hence the interfacial cracks were avoided. To provide a benchmark, reflow of the solders in air using flux was also carried out.
Originality/value
This paper provides information about the effect of UBM thickness on joint strength for plasma fluxless soldering to researchers and engineers.
Details
Keywords
Hyeon Hwang, Soon‐Min Hong, Jae‐Pil Jung and Choon‐Sik Kang
Sn‐Pb and Sn‐Ag bumps (130 μm diameter, 250 μm pitch) made using an electroplating process were studied. As a preliminary experiment, the effects of current density and plating…
Abstract
Sn‐Pb and Sn‐Ag bumps (130 μm diameter, 250 μm pitch) made using an electroplating process were studied. As a preliminary experiment, the effects of current density and plating time on the Sn‐Pb and Sn‐Ag deposits were investigated. The morphology and composition of the plated surface were examined using scanning electron microscopy. The shape and thickness of the solder bumps were also compared. Bump shear testing was performed to measure the adhesion strength between the solder bumps and the under bump metallurgy. In electroplating, the Sn‐Ag plating thickness was proportional to the current density, while plated Sn‐Pb thickness saturated above the limiting current density. The optimal conditions for solder bump fabrication were found at 6 A/dm2 for 3 h in the case of Sn‐Pb bump plating and 6 A/dm2 for 1 h for the Sn‐Ag bump plating. The bump shear strength for Sn‐Ag was found to be higher than that of Sn‐Pb.
Details
Keywords
Kyoo‐Seok Kim, Jae‐Pil Jung and Y. Norman Zhou
The aim of the paper is to study the feasibility of direct ultrasonic bonding between contact pad arrays on flexible printed circuit boards (FPCB) and rigid printed circuit boards…
Abstract
Purpose
The aim of the paper is to study the feasibility of direct ultrasonic bonding between contact pad arrays on flexible printed circuit boards (FPCB) and rigid printed circuit boards (RPCB) at ambient temperature.
Design/methodology/approach
Metallization layers on the RPCB comprised Sn on Cu while the pads on the FPCB consisted of Au/Ni/Cu. Prepared RPCB and FPCB were bonded by ultrasound at ambient temperature using an ultrasonic frequency of 20 kHz, a power of 1,400 W, and 0.62 MPa of bonding pressure. The bonded samples were cross‐sectioned and the joints and microstructures were observed by Field Emission Scanning Electron Microscopy (FE‐SEM) and Energy Dispersive Spectroscopy (EDS). The soundness of the joints was evaluated by pull testing.
Findings
Robust bonding between FPCB and RPCB was obtained by bonding for 1.0 and 1.5 s. This result has confirmed that direct room temperature ultrasonic bonding of Au and Sn is feasible. At a longer bonding time of 3.0 s, cracks and voids were found in the joints due to excessive ultrasonic energy. The IMC (intermetallic compound) between the Sn layer and pads of the RPCB was confirmed as Cu6Sn5. On the FPCB side, Cu6Sn5 and Ni3Sn4 were formed by contact with the facing Sn coating, and mechanically alloyed Cu0.81Ni0.19 was found within the pads. Meanwhile, the strength of bonded joints between FPCB and RPCB increased with bonding time up to 1.5 s and the maximum value reached 12.48 N. At 3.0 s bonding time, the strength decreased drastically, and showed 5.75 N. Footprints from the fracture surfaces showed that bonding started from the edges of the metal pads, and extended to the pad centers as ultrasonic bonding time was increased.
Originality/value
Direct ultrasonic bonding with transverse vibration at ambient temperature between the surface layers of the pads of FPCB and RPCB has been confirmed to be feasible.
Details
Keywords
The purpose of this paper is to examine regional voting patterns in South Korea using the results from six presidential elections since the 1990s.
Abstract
Purpose
The purpose of this paper is to examine regional voting patterns in South Korea using the results from six presidential elections since the 1990s.
Design/methodology/approach
A χ2 test was used to determine the municipalities where a regional voting pattern emerged, and λ correlation coefficients were calculated to examine changes in the regional voting patterns.
Findings
The analyses lead to three key findings. First, voting patterns differ in Yeongnam and Honam: regional voting in Yeongnam is getting weaker, it remains strong in Honam. Second, the tendency to vote along regional lines decreased significantly in the election in which the Honam party fielded a candidate with a Yeongnam appeared identity. Third, regional voting patterns declined but then stabilized at a constant level, regardless of the candidates’ local identity, which was confirmed in “Bu-Ul-Gyeong.”
Originality/value
This paper can empirically verify the manifestation of regional voting pattern and confirm the trend. It is possible to derive a condition for suppressing the regional voting pattern.
Details
Keywords
Seong-Gyu Jeon and Yong Jin Kim
The weapon system of The Navy is the small quantity producing system on multiple kinds. It is consisted of various equipment and the subordinate parts of those which can repair…
Abstract
The weapon system of The Navy is the small quantity producing system on multiple kinds. It is consisted of various equipment and the subordinate parts of those which can repair the damaged part. The operating procedure concerning warship's repair parts managed under these systems is as follows. Firstly, if demand of repair parts occurs from warship which is the operating unit of weapon, then the Fleet(the repair & supply support battalion) is in charge of dealing with these requests. If certain request from warship is beyond the battalion's capability, it is delivered directly to the Logistic Command. In short, the repair and supply support system of repair parts can be described as the multi-level support system. The various theoretical researches on inventory management of Navy's repair parts and simulation study that reflects reality in detail have been carried out simultaneously. However, the majority of existing research has been conducted on aircraft and tank's repairable items, in that, the studies is woefully deficient in the area concerning Navy's inventory management. For that reason, this paper firstly constructs the model of consumable items that is frequently damaged reflecting characteristics of navy's repair parts inventory management using ARENA simulation. After that, this paper is trying to propose methodology to analyze optimal inventory level of each supply unit through OptQuest, the optimization program of ARENA simulation.