PCB表面涂覆用的浸镀银现状

概述了浸镀银作为PCB的最终表面精饰的现状和浸银的诸特性（焊接性、线粘结性、迁移性、电池腐蚀、蠕变腐蚀）。     

适应无铅化的水溶性预涂焊剂

概述了下一代水溶性预涂焊剂的开发和特点,使用于无铅焊接用PCB表面预涂处理。     

光学表面光洁度评述

本文叙述了光学表面光洁度概念、重要性、评定规范、检测方法和仪器装置,以使有关人员对表面质量评定问题引起足够重视,并对出口的光学零件严格检验,以使我们的产品质量得到保证而尽快参与国际竞争,出国创汇或承接国外加工订货。文中还介绍了有关国家标准和美国MIL-0-13830A规范。     

LTCC基板共烧平整度工艺研究

LTCC共烧工艺是基板加工的重要环节,有很多因素会影响产品加工进程。一般来说,从设计上要预先充分考虑,以避免负面因素影响基板共烧效果。介绍了LTCC基板/低温共烧陶瓷基板技术及共烧致密化技术的机理,阐述了LTCC平整度重要性及改善基板表面平整度工艺的优化过程。通过综合比较版图优化前后的内层金属含量、不同尺寸样品加工、结构设计等因素,经过多重试验验证,结果表明,版图优化措施切实可行,可有效提高LTCC基板共烧平整度。     

无铅化热风整平的焊料与选择

文章概述了无铅化热风整平的焊料及其选择。在Sn—Cu中加入少量的Ni（或Co）是无铅化热风整平的焊料的有利选择。     

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...     

提高和改善“无铅化”多层板层间的结合力

文章概述了无铅化多层板的层间结合力问题。依靠传统的粗糙度方法已经受到了挑战,而采用化学结合力应是发展的方向。     

Evaluation of Electrochemical Migration on Flexible Printed Circuit Boards with Different Surface Finishes

This study investigated the influence of three parameters, the distance between electrodes, bias voltage, and surface finish material, on the electrochemical migration (ECM) in flexible printed circuit boards (FPCBs) during water drop testing. The ECM rate increased when the distance between electrodes of opposite polarity was decreased and the bias voltage was increased. Irrespective of the distance between the electrodes and the bias voltage, the growth rate of dendrites from the cathode to the anode decreased with the following order of surface finish material: Cu, electroless Ni, and electroless nickel-immersion gold. The order of the corrosion rate in distilled water with pH 6.5 was the same. Therefore, the ECM rate on the FPCB increased with increasing corrosion rate of the FPCB surface finish material.     

Wetting Kinetics of Eutectic Lead and Lead-Free Solders: Spreading over the Cu Surface

Wetting kinetics of Sn, eutectic Sn-Ag, eutectic Sn-Cu, and eutectic Pb-Sn was studied using real-time in situ monitoring of the triple-line movement, facilitated by a hot-stage microscopy system under a controlled atmosphere. Significantly different kinetics of lead versus lead-free solders is documented. In case of the eutectic lead solder, four characteristic spreading stages were identified. Spreading of lead-free solders features two stages with a sharp change of the spreading rate at the early stages of rather insignificant spreading. Scanning electron microscopy and energy-dispersive x-ray spectroscopy analysis of the resolidified solder surface within a halo region is discussed.     

Creep Life Assessment of Tin-Based Lead-Free Solders Based on Imaginary Initial Strain Rate

The creep properties of tin-based, lead-free solders, Sn-3.0Ag-0.5Cu and Sn-7.5Zn-3.0Bi, were investigated for the temperature range from 298 K to 398 K. The creep rupture time decreases with increasing initial stress and temperature. The Omega method is applied to the analysis of the solder creep curves. The creep rate is expressed by the following formula: , where and Ω are experimentally determined. The parameter , the imaginary initial strain rate, increases with increasing initial stress and temperature. The parameter Ω is temperature dependent, but less dependent on the initial stress. The apparent activation energy for is 108 kJ/mol in Sn-3.0Ag-0.5Cu and 83 kJ/mol in Sn-7.5Zn-3.0Bi. These values are close to the activation energy for the lattice diffusion of tin. The creep rupture time is calculated using the parameters and Ω. The calculated creep rupture time is in good agreement with the measured creep rupture time.     

Effect of Cu concentration on the reactions between Sn-Ag-Cu solders and Ni

The reaction between the Sn-Ag-Cu solders and Ni at 250°C for 10 min and 25 h was studied. Nine different Sn-Ag-Cu solders, with the Ag concentration fixed at 3.9 wt.% and Cu concentrations varied between 0.0–3.0 wt.%, were used. When the reaction time was 10 min, the reactions strongly depended on the Cu concentration. At low-Cu concentrations (≦0.2 wt.%), only a continuous (Ni_1−xCu_x)₃Sn₄ layer formed at the interface. When the Cu concentration increased to 0.4 wt.%, a continuous (Ni_1−xCu_x)₃Sn₄ layer and a small amount of discontinuous (Cu_1−yNi_y)₆Sn₅ particles formed at the interface. When the Cu concentration increased to 0.5 wt.%, the amount of (Cu_1−yNi_y)₆Sn₅ increased and (Cu_1−yNi₆)₆Sn₅ became a continuous layer. Beneath this (Cu_1−yNi_y)₆Sn₅ layer was a very thin but continuous layer of (Ni_1−xCu_x)₃Sn₄. At higher Cu concentrations (0.6–3.0 wt.%), (Ni_1−xCu_x)₃Sn₄ disappeared, and only (Cu_1−yNi_y)₆Sn₅ was present. The reactions at 25 h also depended strongly on the Cu concentration, proving that the strong concentration dependence was not a transient phenomenon limited to a short reaction time. The findings of this study were rationalized using the Cu-Ni-Sn isotherm. This study shows that precise control over the Cu concentration in solders is needed to produce consistent results.     

浅谈电子丝网印刷中PCB的印制技术

丝网印刷在印制电路板(PCB)上具有得天独厚的优势,文中通过分析丝网印刷和电路板印制的特点,介绍电路板丝网印刷各工序的技术要点,以及电路板丝网印刷常用的几种油墨的应用方法。     

A study on the reaction between Cu and Sn3.5Ag solder doped with small amounts of Ni

The reaction between Cu and the Sn-Ag solders doped with different amounts of Ni is studied. Four different solders with the Ag concentration fixed at 3.5 wt.% and Ni concentrations varied between 0.0 wt.% and 1.0 wt.% are used. In contrast to the reaction between Ni and the Sn-Ag solders doped with different amounts of Cu, the type of intermetallic compound formed does not depend on the Ni concentration. The compound Cu₆Sn₅ forms for all the Ni concentrations used. For the Ni-doped solders, the Cu₆Sn₅ phase contains a small amount of Ni. The compound Cu₃Sn appears subsequently between Cu₆Sn₅ and Cu as the reaction time increases. The addition of Ni has the effect of substantially increasing the amount of intermetallic compound at the interface. The addition of Ni also produces two distinct Cu₆Sn₅ regions at the interface. The outer region contains more Ni, and the inner region contains less Ni. This study also finds that, during solid-state aging, the growth of Cu₃Sn becomes slower when Ni is added to the solder. The findings of this study are rationalized using the Cu-Ni-Sn isotherm.     

以钯作扩散阻挡层——一种多功能线路板表面处理方法

电子工业不断的小型化,数种不同互联技术于线路板上电子零件连接及电接点被应用范畴不断增加。基于此用途,线路板组装垫位需被一层最后表面处理保护,如这最后表面处理层可用于不同互联技术,可被称为多功能表面层。钯是一个艮好的镍扩散阻挡层,故此层膜能抵受如焊接及键接之严酷老化测试条件。其两大优点为具有良好热超声波键接性及于无铅焊料之非常优艮焊接性。从预镀导线架过往多年经验已知即使很薄贵金属钯层及金层已可有保证可靠的金线键接性。从这一知识,沉镍浸钯浸金层膜系统（ENIPIG）被研发出来。此崭新表面处理ENIPIG三种金属镀液需互相配合才能于线路板工艺上达成理想多功能层膜。因着其薄贵金属层膜,相对于其他表面处理,可节省颇大的成本。     

基于声表面波微流转换微器件研究

提出了压电基片上液滴转换为微通道内微流体的方法。在128°YX-LiNbO3基片上采用微电子工艺制作两叉指换能器,软光刻工艺制作聚二甲基硅氧烷(PDMS)微通道,镂空印刷电路板,内嵌压电子器件和微通道。两叉指换能器激发声表面波控制液滴与带细孔钢针的接触时间,实现一定量的微流转换。当两叉指换能器上电信号切换时间为9.667s,水微流体输运速度为0.365μL/s时,微流转换量为3.525μL。     

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。     

Sn-Cu、Sn-Ag-Cu系无铅钎料的钎焊特性研究

制备了Sn-0.7Cu、Sn-3.5Ag-0.6Cu钎料,用润湿平衡法测量了钎料对铜的润湿曲线,研究了温度、钎剂活性、钎焊时间对润湿行为的影响,并与Sn-37Pb钎料进行了比较。结果表明:升高温度能显著改善无铅钎料对铜的钎焊性。当温度<270℃时,Sn-0.7Cu的钎焊性明显低于Sn-3.5Ag-0.6Cu钎料;而当温度≥270℃时,两种钎料对铜都会显示较好的润湿性,而Sn-0.7Cu略优于Sn-3.5Ag-0.6Cu钎料。提高钎剂活性能显著增强钎料对铜的润湿性,其卤素离子的最佳质量分数均为0.4%左右。随着浸渍时间的延长,熔融钎料与铜的界面间产生失润现象。无铅钎料的熔点和表面张力较高,是钎焊性较差的根本原因。     

丝网印刷银线路中电化学迁移的电化学阻抗评价

概述了采用电化学阻抗光谱研究丝网印刷银线路电极上的电化学迁移过程。     

表面贴装技术

在介绍表面贴装技术（SMT）TL其流程的基础上,阐述焊接过程中回流焊炉的回流焊原理及回流焊温度曲线,并将实际生产中某印制电路板的实际回流焊温度曲线标准回流焊温度曲线与相对比,结果表明：只要满足实际回流焊温度区域在标准温度范围内,就能满足贴装元器件的性能指标。