Printed circuit board, forPrinted boardBecause many designers do not understand the production process of circuit boards, their designed circuit diagrams are only the most basicCircuit diagram, and cannot be directly used in production.Therefore, it is necessary to modify and edit the circuit file before actual production. It is not only necessary to produce a film that can be suitable for the production process of the factory, but also to produce the corresponding punching data, mold opening data, and other data useful for production.It is directly related to future production projects.
Engineering technicians should understand the necessary production process and master the relevant software production, including common circuit design software such as altium designer, Pads2000, Autocad, etc. They should also be familiar with the necessary CAM software such as View2001CAM350；GCCAM, etc. CAM should includePCB designInput, you canCircuit diagramEdit, correct, repair, and assemble shapes, use disks as media, and outputLight painting, drilling and detection of automated data.
Laser plotter An important aspect of market success is to provide manufacturers with a large number of technical forces in engineering production.At the same time, we also sawJianheCircuit boardManufacturerThere is a large demand for engineering production personnel, and the requirements for the level of engineering and technical personnel are also getting higher and higher.Therefore, we are urged to constantly improve our technical level in order to meet more and higher demands.During the training and study in our company, on the one hand, students should master the use of our company's laser photo machine and its supporting products and laser photo system software, on the other hand, they should be familiar with various electronic CAD as soon as possible/CAM softwareBasic application of.First of all, I wish you all a smooth study and a happy life in our company!
Jianhe circuit board
repair
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Circuit boardMaintenance is a new repair industry.Industrial equipmentDegree of automationThe number of industrial control boards in various industries is increasing. After the industrial control boards are damaged, the high cost of replacing circuit boards (from thousands of yuan to tens of thousands or hundreds of thousands of yuan) has become a headache for enterprises.In fact, these damagedCircuit boardMost of them can be repaired at home, and the cost is only 20% - 30% of the cost of buying a new board, and the time taken is much shorter than that of buying a foreign board.The following describes the basic knowledge of circuit board maintenance.Almost all circuit board maintenance has no drawings and materials, so many people are suspicious of circuit board maintenance. Although various circuit boards are different, the same thing is that each circuit board is composed of various integrated blocksresistance、capacitanceAnd other components, so the damage of the circuit board must be caused by the damage of one or some of the components. The idea of circuit board maintenance is based on the above factors.The circuit board maintenance is divided into two parts: detection and maintenance, of which detection occupies a very important position.Check the basic knowledge of each component on the circuit board until the bad component is found and replaced, then a circuit board will be repaired.The circuit board detection is to check everyelectronic componentThe process of fault finding, determination and correction.In fact, the whole testing process is a thinking process and a testing process that provides logical reasoning clues. Therefore, testing engineers must gradually accumulate experience and constantly improve their level in the process of circuit board maintenance, testing and overhaul.General electronic equipment is composed of thousands of components. When maintaining and overhauling, it will be very time-consuming and difficult to find problems by directly testing and inspecting each component in the circuit board one by one.Then the number based maintenance method from fault phenomenon to fault cause is an important maintenance method.As long as the circuit board detects the problem, it is easy to repair.The above is the introduction of basic knowledge of circuit board maintenance
Development history
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Circuit boardIt has a history of more than 60 years since its invention.History shows that without circuit boards and electronic circuits, flight, transportation, atomic energy, computers, aerospace, communications, household appliances... all these cannot be achieved.The truth is easy to understand.Chips, ICs and integrated circuits are the food of electronic information industry,semiconductor technology Embodies a country'smodernization of industryLevelElectronic information industryDevelopment of.The electrical interconnection and assembly of semiconductors (integrated circuits, ICs) must rely on circuit boards.As Kobayashi Zheng, the author of Japan's Circuit Board Collection, said: "If there is no computer and data, electronic equipment is an ordinary box; if there is no semiconductor and circuit board, electronic components are an ordinary stone." PCB is a promising industry in China, with an annual growth rate of two digits. Many foreign orders are put into China, and there are opportunities.For example, the motherboard in a computer is a circuit board graphics card and a circuit board. In short, a circuit board is just a place to place parts and wires to complete electrical functions.Almost any electrical appliance has a PCB. Its manufacturing process is generally: data and raw materialsscreen printingMounting machinePasterReflow solderingVisual inspection hand plugWave solderingVisually inspect and test the assembly packaging.
Basic Requirements
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The level of PCB engineering production can reflect the design level of the designer, as well as the production process capability and technical level of the PCB manufacturer.At the same time, as the PCB engineering production integrates CAD and CAM, it requires extremely high precision and accuracy, otherwise it will affect the electrical performance of the final electronic products on board, and may cause errors in serious cases, which will lead to the scrapping of the whole batch of printed board products, delay the manufacturer's contract delivery time, and suffer economic losses.Therefore, as a PCB engineering producer, you must always remember that your responsibility is very important. Do not take it lightly, and be careful, serious, and careful again.When processing PCB design documents, you should carefully check whether the received documents comply with the rules formulated by the designer?Can it meet PCB manufacturing process requirements?Are there positioning marks?Is the line layout reasonable?Line to line, line to componentPad, whether the distance between line and through hole, component pad and through hole, and through hole and through hole is reasonable, and whether it can meet the production requirements.Components in 2Dthree-dimensional spaceIs there any conflict on?Is the size of the printed board consistent with the processing drawing?Whether the graphics (such as icons and labels) added in the PCB graphics will cause signal short circuit.Edit and modify some undesirable lines.Is there a process line on the PCB?Whether the solder mask meets the requirements of the production process, whether the solder mask size is appropriate, and whether the character mark is pressed on the devicePadSo as not to affect the quality of electrical installation.
Photo data
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Patchwork
PCB designComplete becausePCB boardThe shape is too small to meet the production process requirements, or a product is composed of several PCBs, so it is necessary to assemble several small boards into a large board with an area that meets the production requirements, or to assemble multiple PCBs used in a product to facilitate the production of electronics.The former is similar to the stamp board. It can not only meet the PCB production process conditions, but also facilitate the electrical assembly of components. It is very convenient to separate them when using;The latter is to assemble several sets of PCB boards of a product together, which is convenient for production, and is also convenient for the complete set of a product.
Generation of light drawing data
The foundation of PCB production isfilmBottom plate.In the early stage of making a film base, it is necessary to make a film base first, and then use the base to take photos or copy.The accuracy of the base drawing must be consistent with the requirements of the printed board, and compensation for the deviation caused by the production process should be considered.The base drawing can be provided by the customer or produced by the manufacturer, but both parties should cooperate and negotiate closely to make it meet the user's requirements and adapt to the production conditions.When the user provides the base drawing, the manufacturer shall inspect and approve the base drawing, and the user can evaluate and approve the original version or the first printed board product.The base map is made by hand drawing, mapping and CAD drawing.With the development of computer technology, the printed board CAD technology has made great progress, and the production process level of printed boards has also been rapidly improved to the direction of multi-layer, thin wire, small aperture, and high density. The original film plate making process can no longer meet the design needs of printed boards, so photo drawing technology has emerged.Use photo plotter to directly send PCB graphic data files designed by CADLight paintingA computer system that controls the photo plotter to use light to draw graphics directly on the negative.Then after developing and fixing, the film base is obtained.The printed board film base plate made by photo technology is fast, accurate and of good quality. It also avoids possible human errors in manual mapping or base drawing, greatly improves work efficiency and shortensPrinted boardOfproduction cycle 。Use ourLaser plotter In a very short time, we can complete the work that many people have been able to complete for a long time in the past, and the thin wires and high-density plates drawn by it are incomparable to manual operation.According to the different structures of laser photo plotters, they can be divided into flat plate type, internal drum type and external drum type.Series of Yuzhiguang CompanyLight paintingThe machine products are all internationally popular outer drum type.The standard data format used by photo plotter is Gerber-RS274 format, which is also the standard data format of PCB design and production industry.GerberThe name of the format is quoted from Gerber, the pioneer of photo machine design and production in the United States.The generation of light drawing data is to transform the design data generated by CAD software into light drawing data (mostly Gerber data), modify and edit it through the CAM system, and complete light drawing pretreatment (plate assembly, mirror image, etc.) to meet the requirements of the production process of printed boards.Then the processed data is sent to the photo plotter, which is converted into raster data by the Raster image data processor. The raster data is sent to theLaser plotter , finish photo painting.
Photo data format
Light paintingData format is the data format of vector photo plotterGerberIt is developed based on data, and extends the data format of vector photo plotter, and is compatible with HPGLHPgraph plotterFormat, Autocad DXF, TIFF and other special and general drawing data formats.Some CAD and CAM developers have also extended Gerber data.
Here is a brief introduction to Gerber data.The official name of Gerber data is Gerber RS-274 format.Each symbol on the code disk of the vector photo printer has a corresponding D-CODE in Gerber data.In this way, the photo printer can control and select the code disk through the D code, and draw the corresponding figure.List the shapes and sizes of the symbols corresponding to D code and D code to get a D code table.This D code table has developed from CAD design toLight paintingIt is a bridge for the machine to use this data for photo drawing.The user is providingGerberCorresponding D code table must be provided at the same time of photo data.In this way, the photo printer can determine which symbol disk should be selected for exposure according to the D code table, so as to draw the correct figure.A D code table should generally include D code, the shape and size of the code disk corresponding to each D code, and the exposure method of the code disk.The most commonly used electronic CAD software in ChinaProtelFor example, the extension of a D code table isAPT，Is an ACSII file,
It can be edited with any non text editing software.D11 CIRCULAR 7.333 7.333 0.000 LINE D12 CIRCULAR 7.874 7.874 0.000 MULTI D13 SQUARE 7.934 7.934 0.000 LINE D14 CIRCULAR 8.000 8.000 0.000 LINE D15 CIRCULAR 10.000 10.000 0.000 LINE D16 CIRCULAR 11.811 11.811 0.000 LINE D17 CIRCULAR 12.000 12.000 0.000 MULTI D18 CIRCULAR 16.000 16.000 0.000 MULTI D19 CIRCULAR 19.685 19.685 0.000 MULTI D20 ROUNDED 24.000 24.000 0.000 MULTI D21 CIRCULAR 29.528
29.528 0.000 MULTI D22 CIRCULAR 30.000 30.000 0.000 FLASH D23 ROUNDED 31.000 31.000 0.000 MULTI D24 ROUNDED 31.496 31.496 0.000 FLASH D25 ROUNDED 39.000 39.000 0.000 MULTI D26 ROUNDED 39.370 39.370 0.000 MULTI D27 ROUNDED 47.000 47.000 0.000 MULTI D28 ROUNDED 50.000 50.000 0.000 FLASH D29 ROUNDED 51.496 51.496 0.000 FLASH D30 ROUNDED 59.055 98.4250.000 FLASH D31 ROUNDED 62.992 98.000 0.000 FLASH D32 ROUNDED 63.055 102.425 0.000 FLASH In the above table, each row defines a D code, including six parameters.
The first column is the D code number, which is composed of the letter 'D' and a number.
The second column is the shape description of the symbol represented by the D code. For example, CIRCULAR indicates that the symbol is circular, and SQUARE indicates that the symbol is square.
The third and fourth columns define the dimensions of the symbol graphics in X and Y directions respectively, and the unit is mil;1mil=1/1000 inch, which is about 0.0254 mm.
The fifth column is the size of the center hole of the symbol figure, which is also in mil.
The sixth column describes the use of the symbol disk. For example, LINE indicates that the symbol is used for scribing, and FLASH indicates that the symbol is used for scribingPadExposure, MULTI means it can be used for both marking and exposure pad.In Gerber RS-274 format, in addition to the symbol disk defined by D code, D code is also used forLight paintingMechanisticExposure control；In addition, some other commands are used to control and run the photo printer.Produced by different CAD softwareGerberThere may be some minor differences in the data format, but the overall framework is Gerber-RS0274.
functional testing
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More dense PCBs, higher bus speed and analog RF circuits pose unprecedented challenges to testingfunctional testingIt requires careful design, thoughtful test methods and appropriate tools to provide reliable test results. Adequate preparation and careful selection of tools will achieve twice the result with half the effort.
significance
functional testingIt is becoming more and more important. However, like online testing, the development of technology and PCB design will limit the scope of testing.Although great progress has been made in the software environment for programming, which helps overcome some of the difficulties, there are still many problems that need to be avoided and better prepared if you want to successfully implement functional testing according to your testing strategy.This paper introduces some factors that should be taken into consideration in the successful implementation of functional testing and the corresponding strategies.Functional testing of electronic products has a history of rise and fall. In the late 1960s, it was the first automated testing method. With the emergence of online testing technology in the late 1970s, functional testing seems destined to give way to online testing, which is increasingly simple and fast in programming and judgment.Now, however, the trend has changed.One problem of online testing is becoming more and more serious, that is, detection mode.According to the analysis of the NEMI (National Electronics Manufacturing Organization), the nodes that can be detected by the end of 2003 will be basically zero. If the detection cannot be carried out, then online testing will be almost useless.
functional testingIt is increasingly used in the post production process of the production line, and even in the test of the mid process, but its system and implementation method are almost completely different from the previous tests.Today's test systems are faster and more compact in most cases. Functional testing is important for verifying the overall functionality of products, maintaining calibration informationISO9000It is indispensable for the program to provide data and ensure the quality of high-risk products, such as medical equipment.
test method
The implementation method of testing is affected by budget, output, UUT design and other factors, and it is the last item that has the greatest impact on what can be measured, and budget and output will limit the testing.In order to get the highest possible fault coverage rate for testing, you must pay attention to the selection of components and PCB layout in the design phase. Unfortunately, this is not always the case. Rushing to enter the market and intense development often disrupt your wishful thinking.
Here is a preliminary analysis of how to deal with these restrictions.Some concessions that have to be made for testing (especially in the early stage of design) may affect the design, but they will make testing easier and improve test failure coverage.Please note that the following questions and suggestions are notTest EngineerMany of these problems will affect each other. Therefore, each problem should be evaluated and flexibly applied when needed.
Before discussing the design, test system, software and test methods, we should first understand the "object" - the product to be tested, which not only refers to the PCB or the final assembly itself, but also needs to understand how many products will be produced, expected faults, etc., including product types
Structure (single PCB/pre made PCB/final product)
test specification
Planned test point
Expected production (per line/day/shift, etc.)
Expected fault type
Obviously, the "budget" is ignored above, but only after understanding the above items can we determine how much a product test will cost, and only after we know what is needed for a comprehensive test of UUT can we begin to discuss the funding issue, and only then can we know how to compromise to complete the work.After the initial report is completed, the company may give you a budget and wish you "good luck" - figuring out what you can do. At this time, you really need "good luck", but there are other things, some of which are listed below.
High density problems
On the surface, the component density seems to befunctional testingIt's not a problem. After all, the main consideration here is "getting the correct output for an input".Admittedly, it is a little too simple, but the actual situation is like this.Apply the givenExcitation signalAfter a certain period of time, UUT will output specific series of dataConnectorConnection should be the only access problem.
But the density of components also has a certain impact. Take a look at the PCB sample (or your own design) in Figure 1, and you have to answer the following questions first;
Is it necessary to connect the calibration circuit?
Is it important to diagnose specific UUT components or areas?
If the answer to the above question is affirmative, is the exploration done by people or by some kind of automatic mechanism?
AdoptedI/O connectorIs it easy to contact or connect?If not, the connector can passNeedle bedIs the through hole mounting part contacted?
Let's discuss these issues one by one.
Calibration circuit
functional testingIt is often used for calibration or verification of analog circuits, including checking the interior of UUT (such as the IF part of RF circuit) to verify its work. To do so, test points or tests may be requiredPad。One problem in high-frequency design is that the relative impedance of the test point (path length, test pad size, etc.) plus the impedance of the probe will affect the performance of the circuit. This should be kept in mind when setting the test area. Automatic mechanical detection and needle bed fixture (discussed later in this article) only need a small test area, which can ease this contradiction. This is mainly because compared with manual operation,The accuracy of the robot itself allows the tester to detect smaller areas.
fault diagnosis
If you just usefunctional testingAs a pass/fail filter without measuring calibration points, this section can be skipped because the application may not require probes at this time.In most cases, the function test is a pass/fail test, because the function test is very slow in diagnosing faults, especially in the case of multiple faults.However, in some industries, functional testing is going deep into the manufacturing process, such asCellular telephoneFor manufacturing, some manufacturers need to carry out some key measurements at the PCB level, that is, during the assembly process before final assembly, which is determined by the nature of mobile phones that are easy to be eliminated.In other words, mobile phones are designed to be assembled at a lower cost, and they are not easy to disassemble. Therefore, verification of functions before final testing can save rework costs and reduce possible waste products (because mobile phones will be damaged when disassembled).
Therefore, sufficient test points are required to probe PCB, for example, to check a PCB with a spacing of 20 milSurface mountingDeviceJ-lead Is not very convenient, andBGAIt is even less likely.Test point spacing shall be 0.040 inch minimum as recommended by SMTA,PadThe spacing between them depends on the element height, probe size, etc. around the test area, but 0.200 inch spacing should be the minimum requirement, especially for manual detection areas.Obviously, test fixtures and robotic probes are more accurate.
Test Design
Undoubtedly, a design that is easy to test is easier to handle in production than a design that is casual.But engineers usually hope to load more technologies in the smallest volume at the lowest cost, which adds online testing andfunctional testingThe limit of contact with the circuit board in.
The market has also responded to such problems. Existing software tools can analyze the design, review according to the rules specified for assembly and test equipment, and put forward suggestions to make PCB easier to produce.If these tools are applicable to your product, it is recommended to analyze each design, at least it can quickly point out where the problem of test contact is found, and its ultimate purpose is to make the product easier to manufacture.
Structural configuration meeting the requirements of high density
High density can be small PCB size, or there are a large number of circuits on UUT, or both. The above title describes that the mechanical and electrical structure of the system must be considered to meet the test requirements.The mechanical problems to be considered include:
In terms of electricity, if it is multilayer board, which is more economical?Is it a multi instrument mode or a switch converter with a few instruments?Depending on the UUT structure or the type of instrument required, the answer may not be easy to come by.
As the output and speed of each production line increase (realizingscale economyOne of the main methods is to improve the productivity of each test equipment.automationfunctional testingIn fact, the loading/unloading time is saved, and no other test systems need to be added. When considering increasing the output, the increased cost of transportation equipment is usually ignored.
The disadvantages of test automation include an initial hardware investment, the time of integration with the production line, whether the test system can keep pace with the speed of the production line, and the problems caused by equipment failure.Offline tester will not directly affectassembly lineIf the tester fails, the product can be taken out of the production line and put aside to continue production, so that the production line will not be affected, but processing time and labor are also problems.
RememberManual testIt is usually possible to connect the UUT with several cables and connectorsNeedle bedCompared with the probe on the fixture, its service life is generally low, so it should be included in the maintenance plan, which can reduce the intermittent failure.
Fixture problems
Due to the difference of production line output, workshop site and labor rate, the fixture can be changed from simplePlywoodTo the complex full-automatic needle bed test fixture connected by the conveyor belt to the assembly line.Obviously, these factors indicate that there is no fixed scheme.
One manual loading double-sided clamp, oneRibbon cableConnect to primaryI/O connectorThe tip mounted probe can contact the key test points on the UUT.This is the ideal design required by a medium-sized factory. The operator must connect the ribbon cable, close the roof and then start the test.There is no need for manual exploration for calibration and diagnosis, because the roof can contact all relevant areas.The ribbon cable and the roof probe wiring should be designed to be easy to replace, because these cables are often bent and worn.
When dealing with fixture suppliers, we should remember these problems and also think about where the products will be manufactured. This is a lotTest EngineerWill be ignored.For example, we assume that the test engineer is in the United StatesCaliforniaHowever, the product is manufactured in Thailand.The test engineer will think that the product needs expensive automatic fixture, because in theCaliforniaThe price of factory buildings is high, so it is required to have as few testers as possible, and also to use automatic fixtures to reduce the employment of high-tech and high wage operators.But in Thailand, these two problems do not exist. It is cheaper to solve these problems manually, because the labor cost here is very low, and the land price is also very cheap. Large factories are not a problem.Therefore, sometimes first-class equipment may not be popular in some countries.
Operator skill level
In high density UUT, if calibration or diagnosis is required, it is likely that manual detection is required, becauseNeedle bedThe contact is limited and the test is faster (using the probe to test UUT can quickly collect data rather than feedback information toEdge connector), so the operator is required to probe the test point on UUT.Wherever it is, make sure that the test points are clearly marked.
Probe types and ordinary operators should also pay attention to the following issues to consider:
Is the probe larger than the test point?
Is there a danger that the probe will short-circuit several test points and damage the UUT?
Is there any electric shock hazard to operators?
Can each operator quickly find out the test points and check them?Is the test point large and easy to identify?
How long does it take the operator to press the probe on the test point to get an accurate reading?If the test time is too long, there will be some trouble in the small test area. For example, the operator's hand will slip due to the test time is too long, so it is recommended to expand the test area to avoid this problem.
After considering the above issuesTest EngineerShould be reassessedTest probeModify the test file to better identify the test point location, or even change the requirements for operators.
Auto Profiling
In some cases, automatic probing will be required. For example, when it is difficult to use manual probing for PCB, or the testing speed is greatly reduced due to the technical level of the operator, the automated method should be considered.
Automatic detection can eliminate human error, reduce the possibility of short circuit at several test points, and speed up the test operation.However, it is important to know that there may also be some limitations of automatic detection, which vary according to the design of suppliers, including:
How fast does the probe move to the next test point?
What is the actual interval required for the probe system?(Generally speaking, it is better than offlineFunction test systemLarger)
Autoprobe is usually not usedNeedle bedThe fixture contacts other test points, and generally it is slower than the production line, so two steps may be required: if the detector is only used for diagnosis, consider using the traditional functional test system on the production line, and put the detector as the diagnostic system on the production line;If the purpose of the detector is UUT calibration, the only real solution is to use multiple systems, which is much faster than manual operation.
How to integrate into the production line is also a key issue that must be studied. Is there still room on the production line?Can the system be connected to the conveyor belt?Fortunately, many new detection systems are compatible with the SMEMA standard, so they can work in an online environment.
boundary scan
This technology should be discussed as early as the product design stage, because it requires special components to perform this task.In UUT with digital circuit as the main part, IEEE 1194 can be purchased（boundary scan ）Supported devices, which can solve most diagnostic problems with little or no detection.Boundary scan will reduce the overall functionality of UUT, because it will increase the area of each compatible device (each chip will increase 4-5 pins and some lines). Therefore, the principle of selecting this technology is that the cost should be able to improve the diagnosis results.It should be remembered that boundary scanning can be used toFlash memoryAnd PLD devices, which further increases the reason for selecting this test method.
How to deal with a limited design?
If the UUT design has been completed and determined, the options are limited.Of course, you can also ask for modification in the next revision or new product, but the process improvement always needs some time, and you still have to deal with it.
The main guideline here is how many tests you can do.It may be enough according to the expected fault type, but if it is not enough, it is usually necessary to achieve a delicate balance between more expensive test systemsProduct sales cost(COGS) andMarginsChoose a more accurate detection method after weighing.Therefore, there is no simple answer.
The best reference for future design isfunctional testingWhen faced with these limitations, record the tests that can be completed within the time range specified by the production line speed and the number of testers on the production line.The time limit is very critical, because it is impossible to let the output make concessions to you, so your job is to sacrifice the test coverage for time, so you will ask for improvement so that these restrictions can be lifted in the future!
