线路板级测试指南

《线路板级测试指南》由会员分享，可在线阅读，更多相关《线路板级测试指南（4页珍藏版）》请在装配图网上搜索。

1、板级测试指南 英Printed-circuit boards used to be works of art, and the PCB designer was an artist as well as a technician. Components had many different shapes, sizes, and colors, and the traces connecting them were graceful arcs in beautiful patterns. 在过去，一块印刷电路板就是一份艺术品，印刷电路板的设计人员不仅仅是一名技术人员还是一位艺术家。器件有不同的形

2、状、大小和颜色，而且连接器件的导线形式优美。Todays boards, by contrast, are boring. On a typical modern digital PCB assembly, for example, the parts are all squat rectangular components, and the traces are laid out with a precision only a computer could love. 相比之下，现在的电路板令人厌烦。例如，在一块标准的数字印刷电路板上，所有的器件都是有棱有角的，布线的精度也只有计算机才可以完

3、成。Test methods for PCB assemblies have changed as well. In the past, nearly all testing was functional testing, and it was performed with bench top instruments or a custom tester. Today, the test engineer has many more options, including in-circuit testers, manufacturing defects analyzers, and sever

4、al types of functional testers. 对印刷电路板装配的测试方法也已经改变了。以前，几乎所有的测试都是功能性测试，使用传统的测试仪器或台式设备就可以完成。今天，测试工程师有很多选择，包括在线测试设备，制造缺陷分析设备和一些功能测试设备。The first choice for many test engineers is the in-circuit tester. This tester gets its name because it tests components that are part of a board assembly; that is, the

5、components under test are in a circuit.测试工程师的第一个选择就是在线测试设备，之所以称之为在线测试仪器是因为它所测试的器件是电路板装配的一部分，也就是受测设备是“在电路中”。Shorts-and-Opens Test短路、开路测试The first test an in-circuit tester performs is a shorts-and-opens test. Solder shorts are a common manufacturing defect, and you must find them before proceeding wi

6、th the component tests. Shorts may cause a PCB to fail other tests and may damage the tester or the board under test if you must apply power to the board. 在线测试完成的第一项测试任务就是短路、开路测试。焊接导致短路是很普遍的制造缺陷，必须在器件测试开始之前发现这一问题。短路可能导致印刷电路板不能通过其它测试，在对电路板上电后，会损坏测试设备或电路板。After performing the shorts and opens test, th

7、e in-circuit tester tests each component on a PCB assembly one at a time. Usually, the test program will first test the passive components, such as resistors, capacitors, and inductors. If none of the passive-component tests fail, the tester will then test active components, such as transistors and

8、ICs. 短路、开路测试完成以后，在线测试仪需要在同一时间对印刷电路板上的每一个器件进行测试。通常，首先对无源器件测试，如电阻、电容和电感。如果所有的无源器件都通过测试，然后对有源器件测试，如晶体管和集成电路。To test passive components, the tester places a test voltage across the component under test and measures the current. For resistors, this is a DC voltage; for capacitors and inductors, its an AC

9、 voltage. To measure component values accurately, most testers can make two-wire, three-wire, or four-wire measurements. 在测试无源器件时，测试设备对被测试的器件施加一个测试电压后，测量电流。对于电阻来说，这个电压是直流的，对于电容和电感来说，这个电压是交流的。为了使测试更加精确，很多测试设备可以构成两线、三线或四线测量。An in-circuit tester tests a digital IC using the ICs truth table. The tester

10、sets the inputs to all combinations of 1s and 0s and looks for the correct logic values on the outputs. The tester does this with a process called back driving, in which it applies a high-current pulse for a short period that overrides the logic value on the input. During that short period, the test

11、er must also capture the output value of the IC.在线测试设备采用真值表来测试数字集成电路。测试设备对输入设置连续的1和0，检测输出端的正确逻辑值。这一过程被称为反向驱动。在这个过程中，对输入端施加一个短时的比逻辑值高的电流，同时测试仪器要捕捉到集成电路的输出值。To perform an in-circuit test, you need a test fixture that connects the circuit nodes on the board under test to the tester. Most in-circuit tes

12、t fixtures use spring-loaded probes and are vacuum actuated. Wires running from the tester interface to the probes carry test signals back and forth. A technician places the board under test on the fixture and activates the vacuum, which pulls the board down onto the pins. Test engineers refer to sp

13、ring-loaded probes as nails and refer to a fixture using spring-loaded probes as a bed-of-nails fixture. 为了完成在线测试，你需要一个测试固定装置，它可以将被测电路板上的节点连接到测试设备上。很多在线测试固定装置是带有弹簧的探针或者采用真空启动的。连接测试设备和探针的导线来回的传递测试信号。技术人员将受测设备放到固定装置上并启动真空装置，这样，电路板就被固定了。测试工程师把带有弹簧的探针当作“钉子”，把带有这种探针的固定装置当作“针床”。 To keep up with changing P

14、CB technology, manufacturers of in-circuit testers have added features in recent years. Many in-circuit testers now have boundary-scan test capability. With boundary-scan testing, you can test interconnections on PCBs without using a probe on each node. 为了跟上变化的印刷电路板技术，近些年来，在线测试设备已经增加很多功能。很多测试设备具有分界扫

15、描的功能，这样，测试人员就可以直接测试印刷电路板上的互连，而没用必要使用探针去测试每一个节点了。In-circuit testers can now also test for solder opens on surface-mounted devices (SMDs), a common manufacturing defect on boards with SMDs. To perform this test, you need a fixture that positions a metal plate over the circuit under test. The tester me

16、asures the capacitance between the plate and each lead of the circuit under test. Since open leads will have a lower capacitance than connected leads, the tester can tell which leads are soldered correctly and which leads are open. 对于表面安装设备来说，焊接开路是一个很普遍的制造缺陷，在线测试设备可以将其测试出来。为了完成这项测试，你需要将一个金属板放置到被测电路的

17、上面。测试设备测量金属板和受测电路的每一条导线。由于开路的导线比连接线的电容要低，所以测试仪器可以检测出哪条导线连接正常，哪条导线是开路。Other Test Options其它测试项目An alternative to the in-circuit tester is the manufacturing defects analyzer (MDA). MDAs detect manufacturing defects, such as shorts and missing components, but they cant test digital ICs. Like in-circuit

18、testers, MDAs use a bed-of-nails fixture to connect a board under test to the tester. 在线测试的另一个任务是生产缺陷分析，包括短路和元器件丢失，但是不能测试数字集成电路。和在线测试一样，生产缺陷分析通过针床将受测设备和测试设备连接起来。MDA manufacturers feel that their testers offer a cost-effective test strategy. These testers cost less than in-circuit testers, and some m

19、anufacturers claim that tests run faster on MDAs. Because most of the faults found at board test are manufacturing defects, fault coverage for MDA tests is nearly as good as fault coverage for in-circuit tests. And, when coupled with functional testing, the fault coverage for the entire process is a

20、s good as or better than in-circuit testing alone. 生产缺陷分析制造商觉得他们的测试设备提供经济有效的测试战略。这些测试设备所需要的费用要比在线测试设备少，而且有些制造商还宣称在生产缺陷分析设备上，测试速度进行的更快。因为在板级测试中发现的大部分故障都是生产缺陷，生产缺陷分析测试到的故障几乎都可以覆盖在线测试所发现的问题。加上功能测试，这个过程中检测到的故障率要比单独进行在线测试故障发现率大。Whats the Problem? 问题是什么？Because in-circuit testers and MDAs test components

21、individually, a PCB assembly can pass an in-circuit or MDA test and still not function properly. The problem might be an interaction between components or an IC that fails when run at normal operating clock rates. For simple assemblies, the number of boards with these problems is small, so many comp

22、anies pass the boards on to final assembly without a functional test. Finding these problems at final assembly costs less than performing a functional test on each board. 在线测试和生产故障发现测试都是对器件单独进行测试，一块印刷电路板可以通过在线测试或生产缺陷测试，但是功能上还可能不是很完全。问题可能出在器件的互连或工作在正常的时钟频率时集成电路就不能正常的运行了。对于简单的装配而言，电路板虽然存在这样的问题，但是数量少，所

23、以很多公司在最后的装配过程中没有对电路板进行功能测试。在最后的装配过程中发现这些问题要比对每一块板进行功能测试所花费的费用少。For complex boards or boards that arent tested with an in-circuit tester, most companies perform a functional test before final assembly. As the name implies, a functional test simulates an operating environment and tests a board against

24、 its functional specification. There are many types of functional testers. 对于复杂的电路板或者没有经过在线测试的电路板而言，很多公司在最后装配之前进行功能测试。正如名字所暗示的那样，功能测试模拟运行环境，与它的功能说明相对比来测试。功能测试设备的类型有很多种。For microprocessor-based boards or boards that fit into a standard bus, such as the PC bus or VME bus, an emulation tester might be

25、a good choice. Emulation testers work by emulating a microprocessor or computer bus to control the circuitry on a board under testOn microprocessor boards, the emulator takes the place of the microprocessor and places the appropriate data, address, and control signals on the microprocessor pins. Bec

26、ause the emulator works exactly like the microprocessor, you write test programs in the assembly language of the microprocessor or in a language that can be compiled to run on the microprocessor. 对于基于微处理器的电路板和配有标准总线，如PC总线或VME总线，仿真测试可能是一个比较好的选择。仿真测试的工作机理就是通过模拟微处理器或计算机总线来控制受测电路板上的电路。对于一个含有微处理器的电路板来说，仿

27、真器代替了微处理器，在微处理器的管脚设置适当的数据、地址和控制信号。因为仿真器的工作完全仿照微处理器，你可以用微处理器的装配语言或可以在微处理器上运行的语言来编写测试程序。For analog or mixed-signal boards, many engineers design and build custom testers. They select a set of instruments to provide test signals and make measurements and then bolt the instruments into a standard, 19-in

28、. rack. Test engineers call these test systems rack-and-stack because of the way they look. If the instruments have a GPIB or serial interface, you can control them with a computer equipped with a similar interface. 对于混合信号的电路板，很多设计者设计和传统的测试设备。他们选择一套设备来提供测试信号和度量，然后将这套设备固定在一个19英寸的架子上。测试工程师将这套设备称之为“堆架式

29、”。如果设备具有通用接口总线或串行接口，你可以通过一个带有相似界面的计算机来控制。Rack-and-stack systems can be large if the test requires many different instruments. These systems can also be slow, because the instruments are only loosely coupled to the computer. To shrink such systems, and improve their performance, many test engineers n

30、ow design test systems using VXIbus instruments. 如果测试需要很多不同的设备，堆架式系统可以做的很大。这一系统也比较慢，因为设备都是简单的连接到计算机上的。为了压缩系统，同时改进系统的性能，许多工程师都使用带有VXI总线的设备来设计测试系统。VXIbus instruments are designed specifically for computer-controlled test applications. They are smaller than their benchtop equivalents because they have

31、no front panels or power supplies. They can achieve higher performance because they communicate with the controlling computer and each other through the VXIbus (a version of the VME computer bus). You can find VXIbus instruments that perform nearly all the functions performed by benchtop instruments

32、. VXI总线设备是特定为计算机控制的测试应用而设计的。因为不需要前置面板或电源，所以和具有类似功能的台式设备相比，体积要小。因为和控制计算机以及彼此之间的通信是通过VXI总线来完成的，所以具有更高的性能。你可以发现有的VXI总线设备几乎可以完成台式设备所完成的所有功能。Which tester is right for you? The answer is, It depends. It depends on the type of PCB assembly, the number of assemblies you must produce each day, the components

33、 on the board, and the resources you have to program and maintain your ATE equipment. Before buying or building a board tester, you should draft a test plan that takes all these factors into account.哪种测试设备适合你？问题是：看情况而定。要看印刷电路板装配的类型，每天你需要生产的数量、电路板上的器件、资金的安排以及设备的维护。在购买或建立一个板级测试系统之前，你应该草拟一份计划，将以上的因素都要考虑进去。