基于STC89C52单片机的温度检测系统设计

为了检测现场温度,并直观反映其变化趋势,设计了基于STC89C52单片机的温度检测系统。利用数字温度传感器DS18B20采集温度信号,该信号送入STC89C52单片机处理,后由液晶显示器LCD12864（ST7920）显示温度值,并绘制出温度变化曲线。实测结果表明,系统可靠性、测试精度及温度趋势曲线绘制达到设计要求。     

网络式温度检测系统

由单片机、模数传感器、传感器组成数据采集系统，经总线传输给微机，由微机分析处理，从而达到检测温度、湿度的目的。     

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。     

表面贴装技术

在介绍表面贴装技术(SMT)及其流程的基础上,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.     

智能化电声器件电声参数测试仪研制成功

南京大学研制成功电声器件电声参数测试仪,该仪器由微机、检测、打印、显示等部分组成,在微机的控制下,一台仪器可替代信号发生器、测量放大器、电平记录仪和滤波器等多台电声测试仪器,可在消声环境下工作,也可在线     

基于零中频正交解调的频率特性测试仪设计

阐述一款零中频正交解调的频率特性测试仪的设计，包括STM32单片机为硬件平台，采用AD9854，被测网络采用RLC串联谐振电路，测试范围为1～40MHz、最小步进100kHz，经单片机进行数据处理，得到信号的相位和幅度，通过液晶显示幅频特性和相频特性曲线。经过测试，该设备能按要求正确绘制被测网络的幅频特性曲线和相频特性曲线，中心频率的相对误差小于0.1%，有载品质因数相对误差小于2%。     

单插杆式烟叶水分速测仪的研制

介绍一种用于烟包水分检测的低功耗插杆式智能测试仪器,论述了测试仪的工作机理、结构和功能特点。测试仪利用低功耗单片机实现智能化快速测试,采用液晶数字显示,可以很直观地检测出烟叶仓库中的烟包温度与水分含量,便于携带、一键式操作,极大地方便了工作人员对烟叶自然发酵过程中的质量管理。     

回流焊炉温曲线的管控分析

回流焊温度曲线记录印刷电路板元件焊接过程的温度变化,是元件焊接质量的主要影响因素。针对用测温板获取回流焊温度曲线的影响因素,对测温流程进行潜在失效效应分析,发现利用测温板频繁进行炉温测试具有较高的风险系数。但通过对回焊炉各温区温度的监控与分析,发现回焊炉的制程能力处于优良状态,潜在失效效应的风险系数较低。研究表明,在获取可靠的炉温曲线后,只需要加强炉温监控即可保证焊接质量。     

基于DDS模块的简易数字频率特性测试仪设计

本文基于DDS技术设计了一套简易数字频率特性测试仪.本系统由DDS模块、单片机、液晶显示屏、键盘、模数转换电路和信号调理电路组成.单片机控制DDS模块产生特定频率的正弦信号,经信号调理电路缓冲、放大后送入被测网络,再经采样保持电路调理后送人ADC采样,最终经单片机处理数据后在液晶屏上显示特性曲线并给出特征信息.经实物测试,本系统设计有人机交互友好、频率测试范围广、硬件易实现等特点,具有较高的应用价值.     

基于AT89C51的数字集成电路测试仪的设计

以单片机AT89C51为核心,通过串口与下位机通信,设计了一种通过电脑操作,单片机控制的数字集成芯片测试仪,该系统能对常用的20种74系列数字集成电路作出准确快速的功能检查。系统主要由控制及测试、上位机通信两部分组成。控制及测试部分以单片机AT89C51为核心组成,上位机通信部分由Vb编写的可视化用户界面和电平转换电路MAX232组成。     

A comparison of PWB warpage due to simulated infrared and wavesoldering processes

Two types of bare, four layer printed wiring board (PWB) test vehicles were designed and fabricated to replicate simplified versions of typical boards produced by PWB manufacturers. The boards were subjected to simulated infrared and wave soldering reflow processes in a small lab-scale oven integrated with a shadow Moire out-of-plane displacement measurement system. The measured warpages were qualitatively and quantitatively analyzed at selected temperatures during the reflow profiles. The results presented compare and contrast the effects that simulated wave and infrared reflow soldering processes have on the warpage of two different PWB designs     

氮气对无铅回流焊温度的影响

氮气属于惰性气体,在焊接中能够提高元件和印制板焊接面的润湿能力,减少氧化程度,加快焊接反应速度.与空气环境中的焊接相比,在氮气环境中焊接,理论上能够降低所需的焊接温度,并维持或提高焊点的质量和可靠性.首先对回流炉内氧气含量进行了标定,进而对氮气环境下焊接温度曲线在焊料液相线上热容量值降低20%时的回流焊接进行了验证,依然达到甚至超过空气焊接下的焊点质量及可靠性指标.     

冷却速率对无铅再流焊焊点质量的影响（待续）

无铅再流焊中冷却速率影响焊点力学性能及可靠性。快速冷却可以细化组织,间接控制金属间化合物厚度和形态,影响焊点断裂模式,提高焊点综合性能。但是由于元件与PCB等材料的热不匹配性而造成的较大应力,易造成元件或焊点失效等。通过对文献中研究结果的总结,设计了炉冷、空冷和水冷等几种再流焊冷却方式,并对焊点进行了强度测试和组织成分...     

冷却速率对无铅再流焊焊点质量的影响(待续)

无铅再流焊中冷却速率影响焊点力学性能及可靠性。快速冷却可以细化组织,间接控制金属间化合物厚度和形态,影响焊点断裂模式,提高焊点综合性能。但是由于元件与PCB等材料的热不匹配性而造成的较大应力,易造成元件或焊点失效等。通过对文献中研究结果的总结,设计了炉冷、空冷和水冷等几种再流焊冷却方式,并对焊点进行了强度测试和组织成分分析,建议工业用最佳冷却斜率控制在3℃/s～6℃/s。     

冷却速率对无铅再流焊焊点质量的影响（续完）

无铅再流焊中冷却速率影响焊点力学性能及可靠性。快速冷却可以细化组织,间接控制金属间化合物厚度和形态,影响焊点断裂模式,提高焊点综合性能。但是由于元件与PCB等材料的热不匹配性而造成的较大应力,易造成元件或焊点失效等。通过对文献中研究结果的总结,设计了炉冷、空冷和水冷等几种再流焊冷却方式,并对焊点进行了强度测试和组织成分分析,建议工业用最佳冷却斜率控制在3℃/s～6℃/s。     

现有封装生产线的改造问题

根据无铅回流焊的工艺特点,论述了对回流炉加热、冷却、助焊剂管理和氮气保护各系统的改造原则和方案,给出了氮气保护系统的评价标准,对罐装氮气和氮气发生器两种供应系统进行了成本估算和对比。     

Optimization modeling of the cooling stage of reflow soldering process for ball grid array package using the gray-based Taguchi method

The current paper introduces an effective numerical technique for optimization of the cooling stage of reflow soldering process. The study aims to optimize the thermal stress of a solder joint and cooling rate of a ball grid array package using the gray-based Taguchi method. The current methodology comprised numerical techniques for computational fluid modeling of the internal flow in the reflow oven coupled with the structural heat modeling at the board and package levels. The Multi-physics Code Coupling Interface (MpCCI) was used as the coupling software. Various parameters, such as printed circuit board density, cooling temperature, inlet velocity, and conveyor speed, were considered. Nine simulated experiment runs based on Taguchi L₉ orthogonal arrays were performed. The optimal parameter settings for multiple performance characteristics were determined and compared with the single performance characteristic. From the analysis of variance (ANOVA) result, the most influential factor for the multiple performance characteristics was found to be the inlet velocity. Simulated experiment results showed that the performance characteristics during the cooling stage in the reflow oven obviously improved. The new approach greatly helps in reducing soldering defects and enhances solutions to lead-free reliability issues.     

回焊炉内氧气体积分数对焊接可靠性的影响

SMT(表面贴装技术)回焊炉工作时,炉中氧气体积分数的差异很大,从100×10–6至10000×10–6不等,在已验证氧气体积分数[(O2)]超过4000×10–6会造成产品不良的前提下,针对500×10–6,1000×10–6,3000×10–6以及4000×10–6这四种不同的氧气体积分数,分别对回焊炉焊接的铜片上的锡焊点进行润湿角、EDS分析,对组装印制电路板(PCBA)上的锡焊点进行X射线、推力、通孔填充量等测试。结果显示,(O2)在4000×10–6以下,元件的焊接可靠性并无明显差异。选择(O2)=4000×10–6可降低回焊炉的氮气用量,节约成本。     

3D thermal model to investigate component displacement phenomenon during reflow soldering

This paper reports the development of a 3D component-level thermal model to investigate the displacement of the components during the reflow soldering process. One of the root causes of displacement is the temperature deviation between the contact surfaces of the components. Therefore, our model examines the temperature distribution at the level of discrete components and not at the level of whole assembly as is the case of general models used in reflow soldering [Whalley DC. A simplified reflow soldering process model. J Mater Process Technol 2004;150:134-44; Sarvar F, Conway PP. Effective modelling of the reflow soldering process: basis construction and operation of a process model. IEEE Trans Compon Pack Manuf Technol C: Manuf 1998;21(2):126-33; Inoue M, Koyanagawa T. Thermal simulation for predicting substrate temperature during reflow soldering process. In: IEEE Proceeding of the 55th ECTC; 2005. p. 1021-6].Our model is based on the thermal or central node theory. This means that the investigated area is divided into thermal cells representing the thermal behaviour of the given material. During the model discretization a nonuniform cuboid cell grid is used, with this the resolution of the model can be refined to focus on areas of interest (e.g. the soldering pads) whilst reducing the involvement with the less important areas (such as the epoxy body of a component). This approach therefore allows to achieve a significant increase of spatial resolution of the calculated temperature distribution in some distinct areas with only a little increase of model complexity. The model is described by common heat conduction and convection equations and these are solved by the finite difference method in order to achieve high calculation speeds and easy implementation. The ability of our single purpose model is then compared with a general purpose FEM analyzer. It results that the calculation accuracy of our model is comparable with more detailed models. Also, its calculation speed and application is much faster and easier.     

再流焊工艺技术的研究

随着表面贴装技术的发展,再流焊越来越受到人们的重视。文中介绍了再流焊的一般技术要求,并给出了典型温度曲线以及温度曲线上主要控制点的工艺参数。同时还介绍了再流焊中常见的质量缺陷,并粗浅地讨论了其产生的原因及其相应对策。