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Posts: 19
Joined: Fri Jan 26, 2018 2:22 am

Method for quickly detecting PCB board failures

Postby liuliying » Wed Apr 24, 2019 6:25 am

Making a PCB board is not a simple process to complete the board, just drill a hole and put the components on it. PCB production is not difficult, the difficulty lies in the troubleshooting after the completion of the production. Whether it is an individual enthusiast or an industry engineer, it is quite a headache for the PCB board to encounter problems during debugging, just like a programmer encounters a BUG. http://www.pcbindex.com/
Some people have a strong interest in debugging PCB boards. Just like programmers solving BUGs, there are many common PCB board problems. Common problems include board design, electronic component damage, line short circuit, and components. The quality and PCB board breakage are not a few.
Common PCB circuit board failures are mainly concentrated on components, such as capacitors, resistors, inductors, diodes, transistors, field effect transistors, etc., the integrated chip and the crystal oscillator are obviously damaged, and the method of judging the fault of these components can be passed. Eyes to observe. The surface of electronic components with obvious damage has obvious burning marks. Such a failure can be solved by directly replacing the problem component with a new one.
Of course, not all electronic components can be visually observed, such as resistors, capacitors, and triodes. In some cases, damage cannot be seen from the surface and requires professional inspection tools. Commonly used inspections include: multimeters, capacitors, etc., when it is detected that the voltage or current of an electronic component is not within the normal range, indicating that there is a problem with the component or the previous component, and directly replace it and check to see if it is normal.
If the component is broken, it can be detected whether it is observed by the eye or by the instrument. However, sometimes when we give the components on the PCB, we will not detect the problem, but the board will not work properly. Case. Many newcomers have no problem with this kind of problem. They can only re-do a board or buy one. In fact, in this case, many times the components are in the process of installation, due to the coordination of various components, there may be performance instability.
In this case, the instrument can no longer help, you can try to judge the possible range of the fault according to the current and voltage, try to narrow down, experienced engineers may be able to quickly determine the fault area, but the specific components are broken. But not 100% certain. The only way is to try to replace the suspect component until the problem component is found. Last year, my notebook motherboard was flooded. When I was repairing the master, I also encountered the failure to detect the fault. I replaced the components three times during the repair process. They are the power supply chip, diode, and USB charging component. The socket is used to charge the device when it is turned off. Finally, it is determined by a wave detection and replacement of the suspect chip, and finally it is determined that a component on the side of the south bridge chip is short-circuited.
The above mentioned are actually the problem of electronic components. Of course, since the PCB circuit board is the foothold of the components, the circuit board failure must exist. The simplest example is to die the tin-plated part, due to the manufacturing process, There is a possibility of wire breakage during PCB corrosion. In this case, if you can't make up the line, you can only solve it with a thin copper wire.
PCB circuit board failure is not very obvious, it is very troublesome to check, and in the process of investigation, there will be a concentration of focus, after the problem is found, there will be an inexplicable sense of accomplishment, the programmer solves the BUG. This kind of mood, I often like to check some hard-to-maintain boards, I think it is a pleasure.
Posts: 19
Joined: Fri Jan 26, 2018 2:22 am

Flexible circuit board FPC surface plating knowledge

Postby liuliying » Tue Apr 30, 2019 5:58 am

Generally, a PCB made of a soft insulating substrate is called a flexible PCB or a flexible PCB, and a rigid-flex type PCB is called a rigid flexible PCB. It adapts to the needs of today's electronic products to the direction of high density and high reliability, miniaturization and light weight, and also meets the strict economic requirements and the need of market and technology competition.
FPC flexible circuit board basics
Soft PCBs are usually classified as follows according to the number of layers and structure of the conductor:
1.1 single-sided flexible PCB http://www.pcbindex.com/
A single-sided flexible PCB with only one layer of conductor and a surface with or without a cover.
The insulating substrate material used will vary with the application of the product.
Commonly used insulating materials are polyester, polyimide, polytetrafluoroethylene, soft epoxy-glass cloth.
Single-sided flexible PCBs can be further divided into the following four categories:
1) No cover layer single-sided connection
The wire pattern of this type of flexible PCB is on an insulating substrate with no coating on the surface of the wire.
Like a normal single-sided rigid PCB.
These products are the cheapest and are often used in applications where environmental protection is not critical.
The interconnection is achieved by soldering, welding or pressure welding. It is commonly used in early telephones.
2) Covered single-sided connection
Compared with the previous class, this type only has a layer of cover on the surface of the wire according to customer requirements.
The pad needs to be exposed when covering, and it can be easily covered in the end area.
If precision is required, it can be in the form of a clearance hole.
It is the most widely used and widely used single-sided flexible PCB, and is widely used in automotive instruments and electronic instruments.
3) Uncovered double-sided connection
This type of land interface can be connected to both the front and the back of the wire.
To this end, a via hole is formed in the insulating substrate at the pad, which can be formed by etching, etching or other mechanical means at a desired position of the insulating substrate.
It is used for two-sided mounting elements, devices, and where soldering is required. There is no insulating substrate in the pad area of ??the via, and such pad areas are typically removed chemically.
4) Covered with double-sided connection
This type differs from the former class in that it has a layer of cover on the surface. But the cover layer has access holes and allows it
Both sides can be terminated and remain covered.
This type of flexible PCB is made of two layers of insulating material and a layer of metal conductor.
It is used when the cover layer and the surrounding devices are required to be insulated from each other, and they are insulated from each other, and the ends need to be connected to both the front and the back.
1.2 double-sided flexible PCB
Double-sided flexible PCB with two layers of conductors.
The application and advantages of this type of double-sided flexible PCB are the same as those of a single-sided flexible PCB. The main advantage is that the wiring density per unit area is increased.
It can be divided into: no metallized holes and no cover layer: a no metallized holes, no cover layer; b no metallized holes, with a cover layer; c with metallized holes, no cover layer ;d has metallized holes, with a cover layer. Double-sided flexible PCBs without overlays are less useful.
1.3 multi-layer flexible PCB
Flexible multilayer PCBs like rigid multilayer PCBs
Multilayer laminate technology enables multilayer flexible PCBs to be fabricated.
The simplest multi-layer flexible PCB is a three-layer flexible PCB formed by coating two layers of copper shielding on both sides of a single-sided PCB.
This three-layer flexible PCB is equivalent in electrical characteristics to a coaxial wire or a shielded wire.
The most commonly used multilayer flexible PCB structure is a four-layer structure in which interlayer interconnections are realized by metallized holes, and the middle two layers are generally a power supply layer and a ground layer.
The advantage of a multilayer flexible PCB is that the substrate film is lightweight and has excellent electrical properties such as a low dielectric constant. Multilayer flexible PCB board made of polyimide film is about 1/3 lighter than rigid epoxy glass cloth. However, it loses single-sided, double-sided flexible PCB. Flexibility, most of these products are not required for flexibility.
1. Flexible circuit board FPC plating
(1) FPC electroplated pre-treated flexible printed board FPC may be contaminated with adhesive or ink on the surface of the copper conductor exposed by the coating process, and may also have oxidation and discoloration due to high temperature process. Tight coatings with good adhesion must remove contamination and oxide layers from the conductor surface to clean the conductor surface. However, some of these pollutions are very strong in combination with copper conductors, and they cannot be completely removed with weak cleaning agents. Therefore, most of them are often treated with a certain amount of alkaline abrasive and brushing. The covering adhesives are mostly rings. Oxygen resin and poor alkali resistance, which will lead to a decrease in bonding strength. Although it is not obvious, in the FPC plating process, the plating solution may infiltrate from the edge of the coating layer, and in severe cases, the coating layer may be peeled off. . In the final welding, the phenomenon of soldering the drill to the underside of the cover layer occurs. It can be said that the pre-treatment cleaning process will have a significant impact on the basic characteristics of the flexible printed board F{C, and the processing conditions must be given full attention.
(2) Thickness of FPC plating When plating, the deposition rate of electroplated metal is directly related to the electric field strength. The electric field strength varies with the shape of the line pattern and the positional relationship of the electrodes. The thinner the line width of the wire, the terminal of the terminal part. The sharper the distance from the electrode, the greater the electric field strength and the thicker the coating at that location. In the applications related to flexible printed boards, the difference in the width of many wires in the same line is extremely large, which makes it more likely to cause uneven thickness of the plating layer. To prevent this from happening, a shunt cathode pattern can be attached around the line. Absorbs the uneven current distributed on the plating pattern to maximize the uniform thickness of the coating on all parts. Therefore, it is necessary to work on the structure of the electrode. Here, a compromise is proposed, which is strict with respect to the requirements of the uniformity of the thickness uniformity of the coating, and relatively relaxed standards for other parts, such as the lead-plated tin for fusion welding, the gold plating layer for metal wire bonding, etc. High, and for the general anti-corrosion of lead-plated tin, the coating thickness is relatively relaxed.
(3) The smudges and dirt of FPC plating have just been plated, especially the appearance is not a problem, but some surfaces will appear stains, dirt, discoloration, etc., especially after the factory inspection. What is different, but when the user receives the check, I find that there is a problem with the appearance. This is caused by insufficient drift, and a residual plating solution on the surface of the plating layer, which is caused by a slow chemical reaction over a period of time. In particular, the flexible printed board is not very flat due to its softness, and the recess is prone to "accumulation" of various solutions, and then it will react and discolor at this portion. In order to prevent this from happening, not only sufficient drifting but also full drifting is required. It is also necessary to carry out sufficient drying treatment, and it is possible to confirm whether or not the drifting is sufficient by a high-temperature heat aging test.
2. Flexible circuit board FPC electroless plating
When the line conductor to be plated is isolated and cannot be used as an electrode, only electroless plating can be performed. Generally, the plating solution used for electroless plating has a strong chemical action, and the electroless gold plating process is a typical example. The electroless gold plating solution is an alkaline aqueous solution having a very high pH. When such an electroplating process is used, it is easy to occur under the coating of the plating liquid, especially if the quality management of the lamination process is not strict and the bonding strength is low, which is more likely to occur.
Electroless plating of the displacement reaction is more likely to occur under the coating layer due to the characteristics of the plating solution, and it is difficult to obtain ideal plating conditions by electroplating using this process.
3. Flexible circuit board FPC hot air leveling
The hot air plain is a technology developed for the coating of lead-tin on rigid printed circuit boards. Because of this technology, it is also applied to flexible printed board FPC. The hot air leveling is to directly immerse the board in the molten lead-slot, and the excess solder is blown off by hot air. This condition is very demanding for the flexible printed board FPC. If the flexible printed board FPC can not be immersed in the solder without any measures, the flexible printed board FPC must be clamped to the middle of the screen made of titanium steel. Then, it is immersed in the molten solder. Of course, the surface of the flexible printed board FPC is also cleaned and coated with flux.
Due to the harsh hot air leveling process conditions, it is easy for the solder to be drilled from the end of the cover layer to the underside of the cover layer, especially when the adhesive strength of the cover layer and the copper foil surface is low, which is more likely to occur frequently. Since the polyimide film is easy to absorb moisture, when the hot air leveling process is used, the moisture absorbing moisture will cause foaming or even peeling of the cover layer due to rapid heat evaporation, so it is necessary to dry and prevent moisture before the FPC hot air leveling. management.
Posts: 19
Joined: Fri Jan 26, 2018 2:22 am

Ultra-comprehensive pcb failure analysis technology

Postby liuliying » Fri May 10, 2019 5:47 am

As the hub of various components and circuit signal transmission, PCB has become the most important and key part of electronic information products. Its quality and reliability determine the quality and reliability of the whole equipment. With the miniaturization of electronic information products and the environmental requirements of lead-free and halogen-free, PCBs are also developing in the direction of high density and high Tg and environmental protection. However, due to cost and technical reasons, PCBs have experienced a large number of failures in the production and application process, and thus caused many quality disputes. In order to clarify the cause of the failure in order to find a solution to the problem and to clarify the responsibility, a failure analysis must be performed on the failure case that occurred. http://www.pcbindex.com/
To obtain the exact cause or mechanism of PCB failure or failure, you must follow the basic principles and analysis procedures, otherwise valuable failure information may be missed, resulting in the analysis can not continue or may get wrong conclusions. The general basic process is to first determine the failure location and failure mode, ie, failure location or fault location, based on failure phenomena, through information collection, functional testing, electrical performance testing, and simple visual inspection. For a simple PCB or PCBA, the location of the failure is easy to determine. However, for a more complex BGA or MCM packaged device or substrate, the defect is not easily observed by the microscope, and it is difficult to determine at a time. This time, other means are needed to determine. The failure mechanism is then analyzed by using various physical and chemical methods to analyze the mechanism that causes PCB failure or defect generation, such as virtual welding, contamination, mechanical damage, moisture stress, dielectric corrosion, fatigue damage, CAF or ion migration, Stress overload and so on. Then the failure cause analysis, that is, based on the failure mechanism and the process analysis, find the cause of the failure mechanism, and if necessary, carry out test verification. Generally, the test verification should be possible as possible, and the cause of the induced failure can be found through the test verification. This provides a targeted basis for the next step of improvement. Finally, according to the test data, facts and conclusions obtained in the analysis process, the failure analysis report is compiled, and the facts of the report are clear, the logical reasoning is strict, the rules are strong, and it is forbidden to imagine.
In the process of analysis, pay attention to the basic principles of using analytical methods from simple to complex, from the outside to the inside, from the destruction of the sample to the use of damage. Only in this way can we avoid losing key information and avoid introducing new artificial failure mechanisms. Just like a traffic accident, if one of the accidents destroys or flees the scene, it is difficult for the Gaoming police to make an accurate liability determination. At this time, the traffic regulations generally require that the party who flees the scene or the site at the scene bear full responsibility. The same is true for the failure analysis of PCB or PCBA. If the soldering iron is used to repair the failed solder joints or the large scissors are used to strongly cut the PCB, then the analysis will not be possible, and the failed scene has been destroyed. Especially in the case of a small number of failed samples, once the environment of the failed site is destroyed or damaged, the real cause of failure cannot be obtained.
Posts: 19
Joined: Fri Jan 26, 2018 2:22 am

Optimizing vehicle PCB defect rate method

Postby liuliying » Sat May 11, 2019 6:24 am

Among the key applications of PCBs today, automotive PCBs occupy an important position. PCB copy board, but due to the special working environment, safety and high current requirements of the car, it has higher requirements on PCB reliability and environmental adaptability, and the types of PCB technology involved are also wide, which is for PCB companies. It is a challenge; for manufacturers who want to develop the automotive PCB market, more understanding and analysis of the new market is needed.
Automotive PCBs place special emphasis on high reliability and low DPPM. So, do our companies have accumulated technology and experience in high reliability manufacturing? Is it consistent with the direction of future product development? In terms of process control, can it be done in accordance with the requirements of TS16949? Has the low DPPM been achieved? These are all to be carefully evaluated, and blindly entering this tempting cake will hurt the company itself.
The following is a representative part of the professional production of automotive PCB companies in the testing process, some special practices are provided to the majority of PCB colleagues for reference:
1, the second test method http://www.pcbindex.com/
Some PCB manufacturers have adopted the “secondary test method” to improve the rate of defects found in the first high-voltage electrical breakdown.
2, bad board foolproof test system
More and more PCB manufacturers have installed “good board marking system” and “bad board error prevention box” in the light board testing machine to effectively avoid human error. The good board marking system identifies the tested PASS board for the test machine, which can effectively prevent the tested board or bad board from flowing to the customer. The bad board error prevention box is the signal that the test system outputs the box opening when the PASS board is tested during the test; otherwise, when the bad board is tested, the box is closed, allowing the operator to correctly place the tested circuit board.
3. Establish a PPm quality system
At present, PPm (Partspermillion, defect rate of parts per million) quality system has been widely used in PCB manufacturers. Among the many customers of our company, the application and achievements of HitachiChemICal in Singapore are the most worthy of reference. More than 20 people in the factory are responsible for the statistical analysis of online PCB quality abnormalities and abnormal PCB quality returns. Using the SPC production process statistical analysis method, each piece of bad board and each piece of defective board returned are classified and statistically analyzed, and combined with auxiliary tools such as micro-slices to analyze which manufacturing process produces bad and defective boards. According to the statistical data results, the problem occurred in the process is purposefully solved.
4, comparative test method
Some customers use different brands of different types of PCBs for comparative testing, and track the PPm of the corresponding batches to understand the performance of the two test machines, so as to select a better performance test machine to test the automotive PCB.
5, improve test parameters
Select higher test parameters to strictly detect such PCB. PCBA OEM foundry materials, if you choose higher voltage and threshold, increase the number of high-voltage read leakage, can improve the detection rate of PCB defective board. For example, a large Taiwan-funded PCB company in Suzhou uses 300V, 30M, and 20 ohms to test automotive PCBs.

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