Study of immersion silver and tin printed-circuit-board surface finishes in lead-free solder applications

The wetting of I-Ag (immersion silver) and I-Sn (immersion tin) printed-circuit-board (PCB) finishes by Sn/Ag/Cu and eutectic Sn/Pb solders was studied in this work with Ni/Au (electroless nickel/immersion gold) and organic solderability preservative (OSP) finishes as baselines. Wetting tests were performed on fresh boards and boards subjected to different preconditioning treatments that simulated the effects of aging, storage, and multiple reflow cycles. When the boards are fresh, the wetting of the I-Sn and Ni/Au finishes is better than that on the I-Ag and OSP finishes. However, after the preconditioning treatments, the wetting of the I-Sn finish degrades the fastest, whereas the wetting of the I-Ag and OSP finishes degrade less through the different preconditioning treatments. The wetting of the Ni/Au finish remains excellent through all the preconditioning treatments. The chemical and microstructural changes in the finishes during aging treatments were evaluated using electron spectroscopy chemical analysis (ESCA), x-ray diffractometry (XRD), and cross-sectioning followed by scanning electron microscopy (SEM). The results indicate that a single lead-free reflow cycle consumes the I-Sn layer faster than a Sn/Pb reflow cycle because of the formation of the Sn/Cu intermetallic compound (IMC). Consequently, I-Sn finished boards having an original Sn thickness of ∼1 μm will not withstand multiple lead-free reflow cycles without significant degradation in wetting but up to two Sn/Pb reflow cycles are still feasible. The minimum thickness of I-Sn required for adequate wetting was evaluated by comparing the wetting after different aging treatments. The exposure of I-Sn samples to 85°C/85% relative humidity (RH) conditions increases the thickness of the Sn-oxide layer, which, above a certain thickness, can degrade wetting. Oxidized copper areas formed on top of the I-Ag surface after exposure to 85°C/85% RH treatment, and this was considered a major factor influencing wetting. The formation of sulfides on I-Ag was detected, but their overall quantity remained too small to have a detectable impact on the wetting.     

表面镀覆层与焊料的界面反应对可靠性的影响

通过对SBGA器件与不同表面镀覆层(OSP,ENIG,HASL和Im-Ag)的PCB板互连形成的SnAgCu焊点在温度循环条件下的可靠性进行研究,对比SnPb焊膏,结合有限元仿真进行分析.结果表明:使用ENIG镀覆层的可靠性最好,SnPb样品的焊点失效率为0.98%,SnAgCu样品只有0.68%.温度循环后SnAgC...     

有机可焊性保护剂的现状与未来

文章概述了无铅化焊接用的五类表面涂（镀）覆材料应用情况,从总体的发展趋势上看,主要是HT—OSP取代HASL的问题。由于PCB高密度化的发展,HASL已经由高峰期走向衰老期,而高温型的HT-OSP开始由发展期走向高峰时期。     

The influence of indium tin oxide deposition on the transport properties at InP junctions

The influence of the deposition of indium tin oxide (ITO) on the electrical properties at n- and p-InP junctions have been investigated by current-voltage-temperature and capacitance-voltage measurements. It was found that the formation of the ITO layer on n-type InP substrates causes the reduction of the barrier height and subsequently forms an ohmic contact. The ITO layer on p-type substrates increases the barrier height by 200–300 meV, and causes a defect-assisted tunneling at low forward bias. The results, therefore, can be explained by the introduction of process induced donor-like defects, with the formation of a thin n⁺-layer in the near-surface, decreasing the barrier height for n-substrates and increasing the barrier height for p-substrates. These results support the buried n⁺/p-junction model for ITO/p-InP solar cell structures.     

The influence of indium tin oxide deposition on the transport properties at InP junctions

The influence of the deposition of indium tin oxide (ITO) on the electrical properties at n- and p-InP junctions have been investigated by current-voltage-temperature and capacitance-voltage measurements. It was found that the formation of the ITO layer on n-type InP substrates causes the reduction of the barrier height and subsequently forms an ohmic contact. The ITO layer on p-type substrates increases the barrier height by 200–300 meV, and causes a defect-assisted tunneling at low forward bias. The results, therefore, can be explained by the introduction of process induced donor-like defects, with the formation of a thin n⁺-layer in the near-surface, decreasing the barrier height for n-substrates and increasing the barrier height for p-substrates. These results support the buried n⁺/p-junction model for ITO/p-InP solar cell structures.     

Effects of different printed-circuit-board surface finishes on the formation and growth of intermetallics at thermomechanically fatigued,small outline J leads/Sn-Ag-Cu interfaces

The effects of printed-circuit-board (PCB) surface finish and thermomechanical fatigue (TMF) on the formation and growth of intermetallic compounds (IMCs) between small outline J (SOJ) leads and Sn-3.0Ag-0.5Cu solder were investigated. The thickness of the IMC layer formed initially at the as-soldered SOJ/Sn-Ag-Cu interface over a Ni/Au PCB surface finish was about 1.7 times of that over the organic solderability preservative (OSP) PCB surface finish. The parabolic TMF-cycle dependence clearly suggests that the growth processes are controlled primarily by solid-state diffusion. The diffusion coefficient for the growth of the total IMC layer at the SOJ/Sn-Ag-Cu interface over the Ni/Au PCB surface finish is the same as that over the OSP PCB surface finish, and thus, the total IMC layer at the SOJ/Sn-Ag-Cu interface over the Ni/Au PCB surface finish is thicker than that over the OSP PCB surface finish. Using the Cu-Ni-Sn ternary isotherm, the anomalous phenomenon that the presence of Ni retards the growth of the Cu₃Sn layer while increasing the initial growth of the Cu₆Sn₅ layer can be addressed.     

Texture of electrodeposited tin layers and its influence on their corrosion behavior

Differences in the degree of corrosion of pure thin tin films electrodeposited on copper substrates were investigated in dependence on the layer thickness and the texture of the tin layers. The change of the preferred orientation of the tin layer deposited by applying different current densities was analyzed using X-ray diffraction. A graphical evaluation was used to determine the degree of corrosion after sample exposition to NaCl contaminations and humidity. Results show that a preferred orientation along the lattice planes (3 2 1) and (2 2 0) enhances the corrosion resistance of the tin layer by about one order of magnitude compared to a non-textured sample based on the corroded area. In contrast, a texture along (1 0 1) and (1 1 2) accelerates the oxidation of tin by a factor of about three to four compared with a randomly orientated specimen. The corrosion dependence on the preferred orientation decreases with increasing layer thickness. Moreover, scanning electron micrographs show no effect to the size of the tin grains on variations of the current density. In summary, changes in the process parameters of the electrodeposition lead to a variation of texture and thus modify the chemical and corrosion properties of the resulting tin layers. Consequently reliability properties like solderability or whisker growth in further applications depend on these parameters.     

多芯片PCB板热布局优化试验研究及数值模拟

应用红外热成像技术,对PCB板芯片组布局优化前后的表面温度进行试验测定,同时利用ICEPAK对PCB板表面温度场进行数值模拟,探索预测芯片组热布局效果的可行途径。试验结果表明布局优化后芯片组表面最高温度较随机布局从151.43℃降低至141℃,降幅为6.89%,布局优化降温效果明显。数值仿真发现PCB板导热系数、发射率、建模方式等因素对结果的准确性影响程度不同: 发射率总体影响较小,而导热系数的影响较为显著,建模时应尽量减少对元件结构的简化。采用改进后的仿真模型对芯片组布局进行计算,结果显示芯片表面温度计算值相对误差最小为0.33%,最大为5.99%,布局优化前后最高温度降低5.61%。仿真值与实验结果符合较好,说明合理运用数值模拟技术可以替代试验对电子元件进行热布局分析。     

The mutual influence of surface energy and substrate temperature on the saturation mobility in organic semiconductors

We report on a mutual correlation between the substrate temperature during semiconductor deposition and the surface energy of the gate dielectric on the charge carrier mobility in bottom gate top contact organic field effect transistors (OFETs) with N,N′-diphenyl-3,4,9,10-perylene tetracarboxylic diimide (DP-PDI) as organic semiconductor.     

Substrate temperature effect on the photophysical and microstructural properties of fluorine-doped tin oxide nanoparticles

Transparent conducting oxide of fluorine-doped tin oxide (FTO) thin films was deposited from chemical solutions of tin chloride and ammonium fluoride using streaming process for electroless and electrochemical deposition (SPEED) at substrate temperature 450, 500, and 530 ℃ respectively. The effect of substrate temperatures on the microstructural properties such as crystallite size, dislocation density, micro strain, volume of the unit cell, volume of the nanoparticles, number of the unit cell, bond length and the lattice constants were examined using XRD technique. Only reflections from (110) and (200) planes of tetragonal SnO₂ crystal structure were obvious. The peaks are relatively weak indicating that the deposited materials constitute grains in the nano dimension. Hall measurements, which were done using van der Pauw technique, showed that the FTO films are n-type semiconductors. The most favorable electrical values were achieved for the film grown at 530 ℃ with low resistivity of 7.64×10^-4Ω·cm and Hall mobility of -9.92 cm²/(V·s).     

PCB技术的革新与进步

文章概述了近几年来在PCB工业中生产技术的革新与进步情况,特别是直流电镀(镀层均匀性、填孔镀等)、表面涂(镀)覆(化学镀镍/钯浸金和直接浸金等)技术的革新与进步,推动了PCB工艺技术的发展。     

Testing the effects of temperature and humidity on printed passive UHF RFID tags on paper substrate

This article is an interesting substrate material for environmental-friendly printable electronics. In this study, screen-printed RFID tags on paper substrate are examined. Their reliability was tested with low temperature, high temperature, slow temperature cycling, high temperature and high humidity and water dipping test. Environmental stresses affect the tag antenna impedance, losses and radiation characteristics due to their impact on the ink film and paper substrate. Low temperature, temperature cycling and high humidity did not have a radical effect on the measured parameters: threshold power, backscattered signal power or read range of the tags. However, the frequency response and the losses of the tags were slightly affected. Exposure to high temperature was found to even improve the tag performance due to the positive effect of high temperature on the ink film. The combined high humidity and high temperature had the most severe effect on the tag performance. The threshold power increased, backscattered power decreased and the read range was shortened. On the whole, the results showed that field use of these tags in high, low and changing temperature conditions and high humidity conditions is possible. Use of these tags in combined high-humidity and high-temperature conditions should be carefully considered.     

浸没膜厚度对固体浸没透镜系统分辨力的影响

考虑了光在固体浸没透镜(SIL)和观测样品之间的薄膜的厚度效应,应用矢量衍射理论研究了半球形SIL系统的光场分布.分析和计算指出,光斑的强度、边瓣强度和光斑大小随薄膜的厚度发生振荡.当厚度一定时,在样品内表面附近,随着离开界面的距离的增加,光斑大小和边瓣强度基本不变,但光强先增大后减小,焦点略微向样品内迁移.薄膜材料的折射率与SIL的折射率相匹配时成像效果较好、分辨率较高.     

Adhesion and Reliability of Anisotropic Conductive Films (ACFs) Joints on Organic Solderability Preservatives (OSPs) Metal Surface Finish

The effect of final metal finishes of Cu electrodes on the adhesion and reliability of anisotropic conductive film (ACF) joints was investigated. Two different metal surface finishes, electroless Ni/immersion Au (ENIG) and organic solderability preservatives (OSPs) coated on Cu, were selected in this study for ACF bonding. The adhesion strength of ACF/OSP joints was higher than that of ACF/bare Cu and ACF/ENIG joints. The fracture sites of the ACF/bare Cu and ACF/ENIG joints were ACF/metal interfaces, while those of ACF/OSP joints were inside the ACF. Transmission electron microscope (TEM) and Fourier-transform infrared (FT-IR) analyses showed that the OSP coating layer on the Cu electrodes reacted with the epoxy resin of the ACFs but still remained at the bonding interface. According to the in-depth X-ray photoelectron spectroscopy (XPS) analysis, additional C-N bonds formed after the OSP-epoxy reaction and the outermost nitrogen of the OSP layer participated in curing of the epoxy resin of the ACF. Therefore, the OSP layer acted as an adhesion promoter to ACFs. Furthermore, this role of the OSP layer enhanced the reliability of the ACF/OSP joints under high temperature and humid environments, as compared to the ACF/ENIG joints.     

激光激发源对声表面波的影响

利用激光激发声表面波及光差分技术研究激光源对声表面波的影响。实验中利用了Nd∶YAG脉冲激光器激发超声,采用632nm的He-Ne激光器基于光束偏转法的光差分检测系统,测量了铝样品表面的声表面波,获得了很好的信号。在此基础上研究了激发源的形状和能量对激发的声表面波幅度的影响。同时从热弹和融蚀机制下讨论激光声表面波的产生。在这两种机制下,声表面波的幅度发生了很大的变化。随着激光能量密度的增加,声表面波的幅度由线性变化转换为非线性变化。这一结果对激光激发声表面波理论研究有一定的指导意义。     

The effects of CO,water vapor and surface temperature on the conductivity of a SnO2 gas sensor

It is shown that the conductivity of a SnO₂ gas sensor depends on the concentration of CO and H₂O in the atmosphere n which it is placed. The experimental data can be explained in a consistent manner by hypothesizing that 1) adsorbed oxygen depletes the surface electron concentration and therefore decreases the conductivity; 2) adsorbed water causes electrons to accumulate at the surface and therefore increases the conductivity; 3) CO increases the conductivity by removing adsorbed oxygen by reacting with it to form CO₂; and 4) adsorbed water catalyzes the CO to CO₂ reaction.     

Photo-degradation of the indium tin oxide (ITO)/organic interface in organic optoelectronic devices and a new outlook on the role of ITO surface treatments and interfacial layers in improving device stability

This work focuses on the effect of light exposure on ITO/organic interface in organic optoelectronic devices, including organic light emitting devices (OLEDs), organic photo-detectors (OPDs) and organic solar cells (OSCs). The results show that irradiation by light in the visible and UV range leads to a gradual deterioration in charge injection and extraction across the interface. A correlation between the performance stability of the devices and the photo-stability of the ITO/organic contacts is established. Studies also show that this photo-induced degradation can be significantly reduced by means of ITO surface treatment or through the insertion of interfacial layers between ITO and the organic layers. X-ray Photoelectron Spectroscopy (XPS) measurements reveal detectable changes in the interface characteristics after irradiation, indicating that the photo-degradation of the ITO/organic contacts is chemical in nature. Changes in XPS characteristics after irradiation suggest a possible reduction in bonds between ITO and its adjacent organic layer. The results shed light on a new material degradation mechanism that appears to have a wide presence in ITO/organic contacts in general, and which may play a key role in limiting the stability of various organic optoelectronic devices such as OLEDs, OSCs and OPDs.     

铁掺杂对氮化镓外延材料表面形貌的影响与改善

铁掺杂是获得高阻氮化镓外延材料的有效方法,但是在某些情况下,铁掺杂会导致材料的表面形貌恶化进而影响高电子迁移率晶体管中二维电子气的电学特性。本文主要研究铁掺杂对氮化镓外延材料表面形貌的影响。相关实验结果表面通过提高氮化镓材料的生长速率可以有效改善其表面形貌,而且电阻率也相应提高,获得了铁掺杂浓度为9×1019cm-3且表面形貌良好的氮化镓外延片,电阻率可以达到1×109Ω.cm。     

化学镍/化学钯/浸金的表面涂覆层的可焊性和可靠性

概述了化学镍/化学钯/浸金(ENEPIG)表面涂(镀)覆层的优点。它比化学镍/浸金(ENIG)有更好的可焊接性和焊接可靠性。化学镍/化学钯/浸金表面涂(镀)覆层应该是有发展前景的。     

The influence of vapor phase cleaning on the composition and the surface roughness of rapid thermal oxides and nitrided oxides

In this paper, the influence of various pre-oxidation cleanings on the Si/SiO₂ interface and the oxide surface roughness is investigated. Different types of Vapor Phase Cleanings (VPC) are performed in an integrated STEAG AST cluster module and are compared to a standard wet cleaning process. The VPC uses Anhydrous Hydrogen Fluoride (AHF) and additional ozone cleaning. Directly after the cleaning, oxidation in pure oxygen (O₂) is carried out in an integrated STEAG AST Rapid Thermal Processing (RTP) cluster module. Nitrided oxides are formed by annealing in pure nitric oxide (NO) gas directly after the oxidation. The nitrogen incorporation and distribution in the oxide is investigated using secondary ion mass spectroscopy (SIMS). The nitrogen concentration at the Si/SiO₂ interface depends on the time and/or temperature of the NO annealing. For a 900°C annealing, the nitrogen incorporation varies from 0.5 at.% for a 5 s anneal to 2.5 at.% for a 60 s anneal. The nitrogen concentration of the oxides can be correlated with the different types of precleaning sequences which seems to be an effect of the different fluorine contents obtained after various cleaning procedures. The surface roughness of oxide layers formed after different pre-cleaning sequences is analyzed by Atomic Force Microscopy (AFM). A decrease in surface roughness is measured for oxidation performed at higher temperature. and for rapid thermal oxides produced after a cleaning procedure using AHF and ozone.