Effect of heat shield locations on rework-induced thermal management in ball grid array solder joint

This study investigated the effectiveness of heat shield placement locations during the rework process to avoid thermal and mechanical damage to adjacent ball grid array components and their solder joints on double-sided printed circuit board assembly. Three types of heat shield placement locations were used: sample X, individual heat shield placement on adjacent components of the rework location; sample Y, a U-shaped, and sample Z, a square-shaped heat shield placed respectively at the heat source location. The dye and pull test results, infrared thermography, and temperature measurements were analysed to understand the relationship between the location of the heat shield and solder joint damage during rework. Heat shield placement at the heat source location on the reworked component can reduce the peak temperatures on the adjacent rework component locations by up to 8.18%. The peak temperatures of the centre and corner of the BGA component can be maintained below 195 °C and 210 °C, respectively to improve the adjacent rework component locations' solder joint quality by reducing solder joint damage by more than 50% solder cracks. This is useful for thermal management during rework involving high-density ball grid array component placements on double-sided printed circuit board assembly.

Kesan Rawatan Termomekanik dengan Mampatan Tunggal terhadap Mikrostruktur dan Sifat Mikromekanik Aloi Pateri Sn-0.7Cu

Aloi pateri bebas plumbum telah digunakan secara meluas sebagai bahan antarasambungan bagi peranti elektronik yang memberikan sambungan elektrik bagi kebolehfungsian dan sokongan mekanik bagi integriti struktur. Rawatan termomekanik merupakan proses metalurgi yang melibatkan gabungan rawatan terma dan pembebanan mekanik. Kajian ini bertujuan untuk mengkaji kesan rawatan termomekanik dengan mampatan tunggal ke atas perubahan mikrostruktur dan sifat mikromekanik aloi pateri Sn-0.7Cu. Aloi pateri Sn-0.7Cu berbentuk bar dipotong kepada lapan sampel berbentuk kiub dengan ukuran 6 mm (p) × 6 mm (l) × 10 mm (t). Empat sampel yang pertama menjalani rawatan haba pada suhu 30 ℃, 60 ℃, 90 ℃ dan 120 ℃ selama 20 minit, diikuti dengan proses mampatan tunggal sebanyak 20% dan pelindapan di dalam medium air. Empat sampel yang berikutnya hanya didedahkan pada rawatan haba sahaja, diikuti pelindapan di dalam medium air digunakan sebagai sampel kawalan. Cerapan mikrostruktur menunjukkan butiran yang kecil dan seragam aloi pateri Sn-0.7Cu terbentuk dengan rawatan termomekanik mampatan tunggal pada suhu 120 °C akibat daripada penghabluran semula butiran. Keputusan kekerasan bagi aloi pateri Sn-0.7Cu selepas rawatan termomekanik mampatan tunggal pada suhu 120 °C telah menunjukkan perubahan yang sedikit iaitu sebanyak 19% berbanding sampel rawatan haba sebanyak 64%. Keputusan modulus terkurang juga menunjukkan tren yang sama iaitu perubahan yang lebih rendah bagi sampel dengan rawatan termomekanik mampatan tunggal pada suhu 120 °C sebanyak 52% manakala sampel rawatan haba sebanyak 69%. Penemuan kajian ini menunjukkan bahawa kesan suhu dalam rawatan termomekanik mampatan tunggal berupaya untuk mengubah suai mikrostruktur dan memberikan kestabilan sifat mikromekanik aloi pateri Sn-0.7Cu berbanding dengan rawatan haba.

Effect of Isothermal Aging and Copper Substrate Roughness on the SAC305 Solder Joint Intermetallic Layer Growth of High Temperature Storage (HTS)

This study aims to evaluate the effect of copper (Cu) substrate surface roughness on the intermetallic compound (IMC) growth and interfacial reaction of SAC305 lead-free solder joint after undergone an aging process. Aging process was conducted using high temperature storage (HTS) at temperature of 150 °C and aging times of 200, 400, 600, 800, and 1000 h. IMC morphology and growth were examined using infinite focus microscope (IFM). Then, the SAC305 solder joint IMC growth kinetic was measured based on power law relationship and diffusion coefficient formula. It was noted that the morphology of IMC for the rougher Cu substrate has scallop-shaped and uniform layer as compared to that of smoother Cu substrate for the initial exposure to the HTS. In addition, Cu substrate with Ra of 579 nm is the turning point for the creation of Cu6Sn5 towards more Cu3Sn of IMC. In addition, Cu substrate with Ra of 579 nm also acts as the turning point for the IMC growth of SAC305 solder joint on Cu substrate for the solid-state diffusion to be happened during 150 °C of aging from grain boundary dominant toward volume diffusion dominant.

Effect of Shock Wave on Constant Load Behaviour of Pb-Free/Cnt Solder Joint

The constant load behaviour of SAC305 solder joint with addition of carbon nanotube (CNT), exposed to shock wave condition was investigated. Formulated SAC305-CNT solder pastes with 0.04 wt. % CNT were manually printed to the printed circuit board (PCB) with copper surface finish to form solder joint. The solder joint was exposed to the shock wave condition via open field blast air test using Trinitrotoluene (TNT) explosive. Nanoindentation approach was used to determine the constant load behavior of the SAC305-CNT solder joint under shock wave condition. The results showed that addition of CNT reduced the indentation depth of SAC305 solder joint at 10 mN peak load for blast test sample and control sample. Indentation depth displacement of SAC305-CNT solder joint for blast test sample and control sample were reduced about ~ 42 and ~56%, respectively, if compared to the SAC305 solder joint for blast test sample and control sample. SAC305-CNT solder joint was experienced minimal changes of stress exponent when exposed to the shock wave. The existence of CNT in the solder joint slows down the depth displacement due to constant load.

Wettability of CNT-Doped Solder under Isothermal Aging

Wettability for lead free solder 99.0Sn-0.3Ag-0.7Cu (SAC237) with addition of different weight percentage carbon nanotube after thermal treatment was investigated. SAC 237 solder powder with flux was mixed with 0.01%, 0.02%, 0.03% and 0.04% carbon nanotubes (CNTs) to form SAC-CNTs solder paste. Printed solder paste on test board with Cu surface finish was then reflow under 270°C temperature and isothermal aging at 150°C for 0,200 and 400 hours. Wettability of SAC-CNT solder was determined by measuring contact angle using optical microscope and image analyzer. As a result, from reflow process right through 400 hours of thermal aging, SAC237 with 0.04% CNT has the lowest contact angle as compared to other SAC-CNTs and SAC237 solder. As a conclusion, addition of carbon nanotubes into solder SAC237 improved their wettability on Cu substrate, especially at 0.04% of CNTs.

Effect of geometric parameters on the performance of p-type junctionless lateral gate transistors

This paper examines the impact of two important geometrical parameters, namely the thickness and source/drain extensions on the performance of low doped p-type double lateral gate junctionless transistors (DGJLTs). The three dimensional Technology Computer-Aided Design simulation is implemented to calculate the characteristics of the devices with different thickness and source/drain extension and based on that, the parameters such as threshold voltage, transconductance and resistance in saturation region are analyzed. In addition, simulation results provide a physical explanation for the variation of device characteristics given by the variation of geometric parameters, mainly based on investigation of the electric field components and the carries density variation. It is shown that, the variation of the carrier density is the main factor which affects the characteristics of the device when the device's thickness is varied. However, the electric field is mainly responsible for variation of the characteristics when the source/drain extension is changed.

Effect of Ca Content on Mechanical Properties of 4N Gold Wire for Quad Flat Nolead (QFN) Stacked Die Package

This paper discusses the effect of two similar gold wire (wire A and wire B) used mainly as a wire bonding material for Quad Flat Nolead (QFN) package. Both wires with diameter of 25.4 μm were bonded using automatic wire bonder by maintaining the temperature at 200°C. The effect of trace elements on the mechanical properties of 4N gold wire has not been widely investigated for some years despite the important of wire-bonding and the move towards fine pitch applications. Due to the element analysis, atomic percentage of Ca in wire B is higher than wire A. Pull strength increase with the increasing of the trace element. The higher pull strength of wire B could improve the yield strength, elastic modulus and recrytallization temperature.

Growth Behaviour of ZnO on Si (100) and Platinum Coated Glass Substrate from Aqueous Solution

Zinc oxide nanorods were grown on Si (100) and Platinum coated glass substrate by the aqueous chemical growth (ACG) in aqueous solution that contained zinc nitrate hexahydrate (Zn(NO3)2•6H20) and hexamethylenetetramine (C6H12N4). The obtained ZnO nanorods are uniformly distributed on the Platinum coated glass substrate surface from 1.5 h to 3 h growth time. Branched hexagonal rods were also found growth on these uniform nanorods. Branched hexagonal rods were found on Si (100) from 2 h to 3 h growth time. A small number of flower-like structures compared to the majority oval type structure suggest that secondary nucleation had occurred during the process of growth. All of the high intensity peaks, including the strong (101) peak, are assigned to wurtzite ZnO hexagonal indicating that the product is pure ZnO. The results found in this study revealed that the type substrate plays a role in determining the surface morphology of ZnO growth.

Microstructure of Solder Joint Interconnect in Used Mobile Phone

A tin-lead solder is generally used to mount an electronic package on to a printed circuit board (PCB) of an electronic devices. In this study, we investigated the microstructure of the solder joint from a four years old used mobile phone. Microstructure and morphology of the joint was obtained using optical and scanning electron microscopy (OM and SEM) respectively. Cracks and voids can clearly be seen in the solder area for the most of the sample observed. Crack up to 10 μm wide appeared to be propagating along the solder line between Cu lead and Cu substrate. Energy dispersive X-ray (EDX) analysis revealed that cracks occurred at the richer tin content. It was not clear the exact mechanism that leads to the existence of the crack. However we believe that thermomechanical cause such as thermal fatigue, void formation and the thicker layer of intermetallic compound contributed to the failure of the solder joint.