Overview
Printed circuit boards (3 sheets)
Engineering and technical personnel should understand the necessary production processes, and master the relevant software production, including Common circuit design software such as Altium Designer, Pads2000, Autocad, etc., but also necessary CAM software such as: View2001, CAM350; GCCAM, etc., CAM should include PCB design input, which can edit, correct, and edit circuit graphics. Repair and imposition, use magnetic disk as the medium material, and output automatic data of light drawing, drilling and inspection.An important aspect of the success of the laser light plotter market is to provide manufacturers with a large amount of technical force in engineering production. At the same time, we have also seen the large demand for engineering production personnel from Jianhe circuit board manufacturers, and the requirements for the level of engineering and technical personnel are getting higher and higher. Therefore, we are urged to continuously improve our technical level in order to meet more and higher demands. During the training and study period of our company, the trainees should master the use of our company's laser light plotter and its supporting products and laser light drawing system software on the one hand, and on the other hand should be familiar with the basic application of various electronic CAD/CAM software as soon as possible. First of all, I wish you all a smooth study and a happy life during your stay in our company!
Jianhe circuit board
Maintenance
Circuit board repair is an emerging repair industry. The degree of automation of industrial equipment is getting higher and higher, so the number of industrial control boards in various industries is also increasing. After the industrial control board is damaged, the high cost required to replace the circuit board (as little as several thousand yuan, as many as tens of thousands or more) Several hundred thousand yuan) has also become a very headache for enterprises. In fact, most of these damaged circuit boards can be repaired in China, and the cost is only 20%-30% of the purchase of a new board, and the time taken is much shorter than that of foreign boards. The following describes the basic knowledge of circuit board maintenance. Almost all circuit board repairs do not have drawings and materials, so many people are skeptical about circuit board repairs. Although various circuit boards are very different, the same thing is that each circuit board is composed of various integrated blocks, resistors, capacitors and It is composed of 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 established based on the above factors. Circuit board repair is divided into two parts: inspection and repair, of which inspection occupies a very important position. The basic knowledge of repairing each device on the circuit board is tested, until the bad parts are found and replaced, then a circuit board is repaired. Circuit board inspection is the process of finding, determining and correcting the failure of each electronic component on the circuit board. In fact, the entire inspection process is a thinking process and a test process that provides logical reasoning clues. Therefore, the inspection engineer must gradually accumulate experience and continuously improve the level in the process of circuit board maintenance, testing, and repair. General electronic equipment is composed of thousands of components. During maintenance and overhaul, it will be very time-consuming and very time-consuming to find problems by directly testing and inspecting each component in the circuit board. Difficult. Then the check-in type inspection method from the fault phenomenon to the cause of the fault is an important method of inspection and repair. As long as the circuit board detects the problem, it is easy to repair. The above is an introduction to the basic knowledge of circuit board maintenance
Development History
The circuit board has a history of more than 60 years since its invention. History has shown that: without circuit boards, without electronic circuits, flying, transportation, atomic energy, computers, aerospace, communications, home appliances... all of this cannot be achieved. The reason is easy to understand. Chips, ICs, and integrated circuits are the food of the electronic information industry. Semiconductor technology reflects a country's industrial modernization level and guides the development of the electronic information industry. The electrical interconnection and assembly of semiconductors (integrated circuits, ICs) must rely on circuit boards. As the author of "Circuit Board Collection" in Japan, Masaru Kobayashi said: "If there are no computers and materials, electronic equipment is equal to an ordinary box; if there are no semiconductors and circuit boards, electronic components are just ordinary stones." PCB is a promising industry in China , There will be a two-digit increase every year. Many foreign orders are put into China, and there are opportunities. For example, the motherboard in a computer is a circuit board, and the graphics card is also a circuit board. In short, the circuit board is just a place for placing parts and wires to complete electrical functions. Almost any electrical appliance has a PCB. Its production process is generally: material raw material screen printing, placement machine placement, reflow soldering, visual inspection, hand insertion, wave soldering, visual inspection, testing, assembly, and packaging.
Basic requirements
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 printed board manufacturer. At the same time, due to the integration of computer-aided design and auxiliary manufacturing in PCB engineering production, extremely high precision and accuracy are required, otherwise it will affect the electrical performance of the final on-board electronic products, and may cause errors in serious cases, which will lead to the entire batch of printed boards. The product is scrapped, which delays the contract delivery time of the manufacturer and suffers economic losses. Therefore, as a PCB engineering producer, you must always keep in mind that your own responsibilities are heavy, don't take it lightly, and be careful, serious, careful, and serious. When dealing with PCB design documents, you should carefully check: Does the received document comply with the rules set by the designer? Can it meet the PCB manufacturing process requirements? Are there any positioning marks? Is the line layout reasonable? Whether the distance between the line and the line, the line and the component pad, the line and the through hole, the component pad and the through hole, and whether the distance between the through hole and the through hole is reasonable and whether it can meet the production requirements. Do components conflict in two-dimensional and three-dimensional space? Does the printed board size match the processing drawing? Whether the graphics (such as icons, annotations) added to the PCB graphics will cause signal short circuit. Edit and modify some unsatisfactory line shapes. 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 logo is pressed on the device pad, so as not to affect the quality of the electrical equipment.
Light drawing data
Imposition
PCB design is completed because the PCB shape is too small to meet the production process requirements, or a product is composed of several PCBs, In this way, it is necessary to combine several small boards into a large board with an area that meets the production requirements, or to combine multiple PCBs used in a product to facilitate the production of electrical equipment. 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 when used; the latter is to assemble several sets of PCB boards of a product together, which is convenient for production and also It is easy to set up a product and be clear.
Generation of light drawing data
The basis of PCB production is the film master. In the early days of making a film base, it was necessary to make a film base first, and then use the base map to take a photo or reproduce it. The accuracy of the base map must be consistent with that required by the printed board, and compensation for deviations caused by the production process should be considered. The base map can be provided by the customer or produced by the manufacturer, but the two parties should cooperate and negotiate closely so that it can not only meet the requirements of the user, but also adapt to the production conditions. In the case that the user provides the base map, the manufacturer shall inspect and approve the base map, and the user can evaluate and approve the original or the first printed board product. The basemap production methods include manual drawing, mapping and CAD drawing. With the development of computer technology, printed circuit board CAD technology has made great progress, and the level of printed circuit board production technology has continued to increase rapidly in the direction of multi-layers, thin wires, small apertures, and high density. The original film-making process is no longer possible. To meet the design needs of printed boards, light painting technology emerged. Using a light plotter, you can directly send the CAD-designed PCB graphic data file to the computer system of the light plotter, and control the light plotter to draw graphics directly on the film using light. Then, after developing and fixing, the film master is obtained. The printed circuit board film master produced by light painting technology is fast, accurate, and of good quality. It also avoids human errors that may occur when manually mapping or drawing the base map, greatly improving work efficiency and shortening the printed board. Production cycle. Using our company's laser light plotter, you can complete the work that many people can complete in a short period of time, and the thin wires and high-density base plates drawn by it are also incomparable by manual operation. According to the different structure of the laser light plotter, it can be divided into flat plate type, internal drum type (Internal Drum) and external drum type (External Drum). Yuzhiguang's series of photoplotters are all of the internationally popular outer roller type. The standard data format used by the light plotter is the Gerber-RS274 format, which is also the standard data format for the printed board design and production industry. The naming of the Gerber format is quoted from the pioneer in the design and production of light plotters-Gerber Corporation of the United States. The generation of light drawing data is to convert the design data generated by CAD software into light drawing data (mostly Gerber data), which is modified and edited by the CAM system to complete light drawing preprocessing (imposition, mirroring, etc.) to achieve The requirements of the printed board production process. Then the processed data is sent to the light plotter, which is converted into raster data by the raster image data processor of the light plotter. The raster data is sent to the laser light plotter through the high-speed compression reduction algorithm to complete the light drawing .
Gerber data format
The gerber data format is developed based on the Gerber data of the vector gerber data format. The data format of the light plotter has been expanded and is compatible with HPGL HP plotter format, Autocad DXF, TIFF and other special and general graphics data formats. Some CAD and CAM developers have also extended the Gerber data.
The following 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 light plotter has a corresponding D code (D-CODE) in the Gerber data. In this way, the light plotter can control and select the code wheel through the D code, and draw the corresponding graphics. List the shape and size of the symbols corresponding to the D code and the D code to obtain a D code table. This D code table becomes a bridge from CAD design to light drawing by the light plotter using this data. The user must provide the corresponding D code table while providing the Gerber light drawing data. In this way, the light plotter can determine which symbol disc should be used for exposure according to the D code table, so as to draw the correct graphics. In a D code table, it should generally include D codes, the shape and size of the code disc corresponding to each D code, and the exposure mode of the code disc. Take a D code table of the most commonly used electronic CAD software Protel in China as an example. Its extension is .APT, which 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 CULTI MCULAR 12.000 D13 SQUARE 16.000 16.000 0.000 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 D24 ROUNDED 31.496 31.496 0.000 39.000 ROUND 39.000 ROUND 39.000 ROUND 39.000 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 98.425 0.000 FLASH D31 ROUNDED 62.992 98.000 0.000 FLASH D32 ROUNDED 63.055 102.425 There is one defined in the previous table 0.000 FLASH D32 ROUNDED 63.055 102.425 Code, contains 6 kinds of parameters.
The first column is the D code serial number, which consists of the letter ‘D’ plus a number.
The second column is the description of the shape of the symbol represented by the D code. For example, CIRCULAR indicates that the shape of the symbol is circular, and SQUARE indicates that the shape of the symbol is square.
The third and fourth columns respectively define the X- and Y-direction dimensions of the symbol graphics, in mil; 1mil=1/1000 inch, which is approximately equal to 0.0254 mm.
The fifth column is the size of the center hole of the symbol graphic, and the unit is also mil.
The sixth column describes the use of the symbol disk, such as LINE means this symbol is used for marking, FLASH means it is used for pad exposure, and MULTI means it can be used for both marking and exposure Pad. In the Gerber RS-274 format, in addition to using the D code to define the symbol disk, the D code is also used for the exposure control of the light plotter; in addition, some other commands are used for the control and operation of the light plotter. The Gerber data format generated by different CAD software may have some small differences, but the overall framework is Gerber-RS0274 format unchanged.
Functional test
Description
Dense PCBs, higher bus speeds, and analog RF circuits, etc., have brought unprecedented challenges to testing. Functional testing in this environment requires careful design, well-thought-out test methods and appropriate tools to provide credible test results. Sufficient preparation and careful selection of tools can achieve a multiplier effect.
Significance
Functional testing 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 programming software environment to help overcome some of these difficulties, if you want to successfully implement functional testing in accordance with your testing strategy, there are still many problems that need to be avoided and more careful preparations must be made. This article introduces some factors and countermeasures that should be considered for the successful implementation of functional testing. Electronic product functional testing has a history of its ups and downs. It was the first automated testing method in the late 1960s. With the emergence of online testing technology in the late 1970s, functional testing seemed destined to give way to programming and judgment that became easier and faster. . Today, however, the trend has changed again. One problem with online testing is getting more and more serious, that is, the detection method. According to the analysis of the US NEMI (National Electronics Manufacturing Organization), the number of nodes that can be detected by the end of 2003 will basically be zero. If detection is not possible, then online testing is almost useless.
Functional testing is increasingly being used in the post-production process, and even for mid-process testing, but its system and implementation methods are almost completely different from previous tests. Today's test systems are faster in most cases and have more compact structures. Functional testing is useful for verifying the overall functionality of the product, maintaining calibration information, providing data to the ISO9000 program, and ensuring the quality of high-risk products, such as medical equipment. Indispensable.
Test method
The implementation method of the test is affected by factors such as budget, output, and UUT design, and it is the last item that affects what can be measured Maximum, budget and output will limit the items tested. In order to get the highest possible fault coverage in the test, you must pay attention to the selection of components and PCB layout during the design stage. Unfortunately, this is not always the case. The eagerness to enter the market and intense development will often disrupt you. 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 stages of design) may affect the design, but make testing easier and improve test failure coverage. Please note that the following problems and suggestions are not something that every test engineer has to face or need to solve. Many of these problems will affect each other. Therefore, each problem should be evaluated and applied flexibly when needed.
To be testedProduct testingWhat are the requirements?
Before discussing the design, test system, software, and test methods, you must first understand the "object"-the product to be tested. This not only refers to the PCB or the final assembly itself, but also Understand how much will be produced, expected failures, etc., including: product type
structure (single PCB/pre-made PCB/final product)
test specifications
< p>Planned test pointsExpected output (per line/day/every shift, etc.)
Expected failure type
It is obvious that the above ignores the "budget "But only after understanding the above items can we determine how much it will cost to test a certain product. We will start discussing funding issues after we have figured out what is required to fully test the UUT. Only at this time 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"-thinking about what you can do, you really need "good luck" at this time, but there are other things, listed below Some.
High density problem
On the surface, component density does not seem to be a problem for functional testing. After all, the main consideration here is "give an input And get the correct output". It is true that it is a bit too simple, but this is the actual situation. When a given excitation signal is applied to the UUT input, the UUT will output a specific series of data after a certain period of time. Connecting to the I/O connector should be the only access problem.
But the component density also has a certain impact. Take a look at the PCB sample (or your own design) in Figure 1, you have to answer the following questions first;
Need to connect the calibration circuit Is it?
Is it important to diagnose specific UUT components or specific areas?
If the answer to the above question is affirmative, should the detection be done by humans or by some kind of automatic mechanism?
Do you want to use an automated test device?
Is the I/O connector used easily accessible or connected? If not, is the connector a through-hole mount that can be accessed through the needle bed?
Let’s discuss these issues one by one.
Calibration circuit
Functional testing is often used for the calibration or verification of analog circuits, including checking the interior of the UUT (such as the intermediate frequency part of the radio frequency circuit) to verify To do its work, it may require test points or test pads. A problem with 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, while automatic mechanical detection Compared with the needle bed fixture (discussed later in this article), it only needs a smaller test area, which can alleviate this contradiction. This is mainly due to the accuracy of the automatic machine itself that allows the tester to detect a smaller area compared with manual operation. .
Troubleshooting
If you only use functional tests as pass/fail screening without measuring calibration points, you can skip this section because The application may not need to use the probe at this time. In most cases, functional tests are passed/failed detection. This is because functional tests are 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 as cellular phone manufacturing. Some manufacturers need to perform certain key measurements at the PCB level, that is, during the assembly process before final assembly. It 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, so verifying functions before final testing can save rework costs and reduce possible waste (because the mobile phone will be damaged when it is disassembled).
So to probe the PCB, you need to have sufficient test points. For example, it is not very convenient to check the J-leads of a surface mount device with a pitch of 20 mils, and BGA is even more impossible. According to the recommendations of the Surface Mount Technology Association (SMTA), the minimum interval between test points is 0.040 inches. The interval between the pads depends on the height of the components around the test area, the size of the probe, etc., but the 0.200 inch interval should be the minimum requirement. Especially the manual exploration area. Obviously, the test fixture and automatic mechanical probe are more accurate.
Test Design
There is no doubt that a design that is easy to test is easier to handle in production than a casual design. But engineers usually want to pack more technology in the smallest volume at the lowest cost. This idea increases the limit of contact with the circuit board in online testing and functional testing.
Responding to this kind of problem market, there are software tools that can analyze the design, review according to the rules stipulated by the assembly and test equipment, and put forward suggestions to make the PCB easier to produce. If these tools are suitable for your product, it is recommended to analyze each design, at least it can quickly point out where the test contact problems are found, and the ultimate goal is to make the product easier to manufacture.
Structural configuration that meets high-density requirements
High-density can be a small PCB size, a large number of circuits on the UUT, or both , The above title indicates that the mechanical and electrical structure of the system must be considered to meet the requirements of the test. The issues to be considered in the mechanical aspect are:
How to support UUT
Test area
Multi-layer board testing (Can the tester do parallel testing?)< /p>
I/O connector
In terms of electrical, if it is a multilayer board, which one is more economical? Is it a multi-instrument method or a switching converter plus a small number of instruments? Depending on the structure of the UUT or the type of instrument required, the answer may not be easy to come up with.
Automatic testing orManual testing?
As the output and speed of each production line increase (one of the main ways to achieve economies of scale is to increase the productivity of each test device), it should be considered whether the testing process can be automated. Automated functional testing actually saves the loading/unloading time and does not need to add other test systems. When considering the increase in output, the increased cost of transportation equipment is usually not taken into account.
The shortcomings of test automation include an initial hardware investment, the time to integrate with the production line, whether the test system can keep pace with the production line speed, and the production problems if the equipment fails, and so on. The offline tester will not directly affect the assembly line. If the tester fails, the product can be taken out of the production line and set aside to continue production, so that the production line will not be affected, but processing time and labor are also a problem.
It should be remembered that manual testing may usually use several cables and connectors to connect to the UUT. Compared with the probes on the needle bed fixture, these cables generally have a lower service life, so they should be included in maintenance In the plan, this can reduce intermittent failures.
Fixture problem
Due to different production line output, workshop space and labor rate, the fixture can range from simple plywood with plugs and connecting cables to complex A fully automatic needle bed test fixture connected to the assembly line by a conveyor belt. Obviously, these factors indicate that there is no fixed solution.
A double-sided fixture is manually loaded, a ribbon cable is connected to the main I/O connector, and the probe mounted on the top can touch 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 top plate and then start the test. There is no need for manual inspection for calibration and diagnosis, because the top plate can touch all relevant areas. The ribbon cable and the top plate probe wiring should be designed to be easy to replace, because these cables are often bent and subject to wear.
When dealing with fixture suppliers, keep these issues in mind, and at the same time think about where the product will be manufactured. This is a place that many test engineers will ignore. For example, we assume that the test engineer is in California in the United States, but the product is manufactured in Thailand. Test engineers will think that products need expensive automated fixtures, because the California plant is expensive, requiring as few testers as possible, and automated fixtures are needed to reduce the employment of high-tech and high-paid operators. But in Thailand, these two problems do not exist. It is cheaper to let people solve these problems 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.
Technical level of the operator
In the high-density UUT, if calibration or diagnosis is required, it is likely to need to be explored manually. This is due to the needle bed Limited access and faster testing (using probes to test UUTs can quickly collect data instead of feeding information back to the edge connector) and other reasons, so the operator is required to probe the test points on the UUT. No matter where it is, make sure that the test point is clearly marked.
The probe type and ordinary operators should also pay attention to the issues that need to be considered:
Is the probe larger than the test point?
Is the probe in danger of short-circuiting several test points and damaging the UUT?
Is there an electric shock hazard to the operator?
Can each operator quickly find the test point and conduct an inspection? Are the test points large and easy to identify?
How long does it take for the operator to press the probe on the test point to get an accurate reading? If the time is too long, some troubles will occur in the small test area, such as the operator’s hand sliding due to the long test time, so it is recommended to expand the test area to avoid this problem.
After considering the above problems, the test engineer should re-evaluate the type of test probe, modify the test file to better identify the location of the test point, or even change the requirements for the operator.
Automatic detection
In some cases, automatic detection is required, for example, when PCB is difficult to detect manually, or when the technical level of the operator is limited, the test speed is greatly reduced , Then you should consider using automated methods.
Automatic detection can eliminate human error, reduce the possibility of short circuit of several test points, and speed up the test operation. But be aware that automatic detection may also have some limitations, which vary according to the supplier’s design, including:
UUT size
number of sync probes
< p>How close are the two test points?Test the positioning accuracy of the probe
Can the system detect UUT on both sides?
How quickly does the probe move to the next test point?
What is the actual interval required by the probe system? (Generally speaking, it is larger than the offline functional test system)
Automatic detection usually does not use needle bed fixtures to contact other test points, and generally it is slower than the production line, so two steps may be taken: if The detector is only used for diagnosis. You can consider using a traditional functional test system on the production line, and place the detector as a diagnostic system on the side of the production line; if the purpose of the detector is UUT calibration, then the only real solution is to use multiple A system, it is still 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 for the production line? Can the system be connected to the conveyor belt? Fortunately, many new detection systems are compatible with SMEMA standards, 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 specialized components to perform this task. In UUTs based on digital circuits, devices with IEEE 1194 (boundary scan) support can be purchased, so that most diagnostic problems can be solved with little or no detection. Boundary scan will reduce the overall functionality of the UUT, because it will increase the area of each compatible device (each chip adds 4 to 5 pins and some lines), so the principle of choosing this technology is the cost. Should be able to improve the diagnosis results. It should be remembered that boundary scan can be used to program flash memory and PLD devices on the UUT, which further increases the reason for choosing this test method.
How to deal with a limited design?
If the UUT design has been completed and finalized, the options are limited at this time. Of course, you can also request to make changes in the next revision or new product, but process improvement always takes a certain amount of time, and you still have to deal with it.
The main guiding idea here is how many tests you can do. According to the expected failure type, it may be enough, but if it is not enough, it is usually necessary to strike a delicate balance between the more expensive test systems, and choose a more accurate detection after weighing the UUT's cost of goods sold (COGS) and the marginal profit. Method. So, the answer is that there is no simple answer.
The best reference for future design is the completion of functional testing when restricted. When faced with these limitations, you should write down the tests that can be completed within the time range specified by the production line speed, and the production line The number of testers owned. Time limitation is very important, because it is impossible to make production yield concessions to you, so your job is to sacrifice test coverage for time, so you will require improvement so that these limitations can be lifted in the future!