We pulled into the parking lot a little before 5:00 pm. The volunteers were already gathered and had made two long lines of empty boxes. Our two trucks were filled with the food that Free the Need volunteers had collected throughout the week; food that would have otherwise ended up in landfill. The food is brought to this local Klamath River center to be distributed to families in need.
The volunteers worked together like a well-oiled machine. Vegetables, fruit, canned foods, bread, cheese, and milk, along with flowers, were put into the boxes. After checking them to make sure the food looked evenly distributed, everyone lined up to receive boxes for their families and neighbors. The whole operation was joyful, friendly and took less than an hour.
In addition to Klamath River, Free the Need delivers food to families in San Francisco. The organization is all volunteer, so any cash donations received go 100% to food distribution. Free the Need believes in an abundant universe. Its volunteers are breaking the chain of poverty by distributing surplus food that would otherwise go to waste. If a family is freed of the need for food, they can put more energy into creating a better life. Free the Need believes that there is enough of what people need to go around, and that once people feel filled up, they have enough surplus to give to others.
I also believe in an abundant universe, and am honored to be a member of Free the Need’s board of directors. I attended a planning meeting for 2018, and was impressed by the care with which plans and procedures for the new year were discussed. Free the Need is launching a fund-drive to raise money to purchase an additional truck needed for food transportation. They are also looking into a storage facility in San Francisco to support their growing work. For more information, or if you would like to volunteer or make a gift of support, please visit their website at www.freetheneed.org/.
Now share a summary of the difficult problems of carefully organized PCB design techniques 1 How to choose PCB board? The PCB sheet must be selected to meet the design requirements and mass production and cost balance. The design requirements consist of two parts: electrical and mechanical. This material problem is usually more important when designing very high-speed PCB boards(frequencies greater than GHz). For example, the commonly used FR-4 material, the dielectric loss at several GHz frequencies will have a great influence on signal attenuation and may not be useful. For electrical purposes, it is important to note whether the dielectric constant and the dielectric loss are compatible with the designed frequency. 2 How to avoid high frequency interference? The basic idea of avoiding high-frequency interference is to minimize the interference of high-frequency signal electromagnetic fields, the so-called crosstalk. You can use the distance between the large high speed signal and the analog signal, or add group/shot tracks next to the analog signal. Attention should also be paid to the digital noise interference to the simulated ground. 3 In high-speed design, how to solve the problem of signal integrity? Signal integrity is basically a problem of impedance matching. The factors that affect impedance matching include the architecture and output impedance of the signal source, the characteristic impedance of the alignment, the characteristics of the load end, and the topology architecture of the alignment. The solution is to rely on the topology of the terminal and the alignment. How is the 4 difference distribution line method realized? The difference pair wiring has two points to note. One is to keep the length of the two lines as long as possible, and the other is the distance between the two lines(this distance is determined by the difference impedance) to remain unchanged, that is, to maintain parallel. There are two ways to parallel, one is to walk on the same ease-by-side, and the other is to walk on the over-under two adjacent layers. Generally speaking, there are more ways to implement the former side-by-side. 5 For a clock signal line with only one output, how to achieve a difference distribution line? To use the difference distribution line, it must be that the signal source and the receiving end are also differential signals. Therefore, it is impossible to use a difference distribution line for a clock signal with only one output http://www.pcbindex.com/ 6 Can a matching resistor be added between the difference lines at the receiving end? The matching resistance between the difference lines at the receiving end is usually added, and its value should be equal to the value of the difference impedance. This will make the signal better. 7 Why do differential pairs of wiring have to be close and parallel? The wiring of differential pairs should be properly close and parallel. The so-called appropriate proximity is because this spacing affects the value of the differential impedance, which is an important parameter for designing differential pairs. The need for parallelism is also due to maintaining the consistency of differential impedance. If the two lines are suddenly and suddenly close, the differential impedance will be inconsistent, which will affect signal integrity and time delay. How to deal with some theoretical conflicts in actual wiring? 1. Basically, it is right to divide the Modulo / number separation. It should be noted that the signal alignment should not cross the segmented place(moat) as far as possible, and that the reflux current path of the power supply and signal should not be too large. 2. Crystalline vibration is an analog positive feedback oscillation circuit. To have a stable oscillation signal, it must satisfy the specification of loop gain and case, and the oscillation specification of this analog signal is easily disturbed, even if the addition of frame guard tracks may not be able to completely isolate the interference. And far away, the noise on the ground plane will also affect the positive feedback oscillation circuit. Therefore, it must be possible to close the distance between the crystal vibration and the chip. 3. There are indeed many conflicts between high-speed wiring and EMI requirements. However, the basic principle is that the resistance capacitance or ferritehead added by EMI can not cause some electrical characteristics of the signal to be inconsistent with the specification. Therefore, it is best to use the technique of scheduling alignment and PCB stacking to solve or reduce EMI problems, such as high-speed signal walking layers. Finally, the resistance capacitance or ferrite bead is used to reduce damage to the signal. 9 In high-speed PCB design, the blank area of the signal layer can be copper, and how should the copper of multiple signal layers be distributed on the ground and connected power supply? In general, the vast majority of copper dressing in blank areas is grounded. Only pay attention to the distance between the copper and the signal line when laying copper next to the high-speed signal line, because the copper applied will reduce the characteristic impedance of the alignment. Care should also be taken not to affect the characteristic impedance of its layer, for example in the structure of a real layer. Is it possible to calculate the characteristic impedance of the signal lines above the power supply plane using a microstrip line model? Can the signal between the power supply and the ground plane be calculated using a banded line model? Yes, the power supply plane and the ground plane must be regarded as reference planes when calculating the characteristic impedance. For example, the four-layer board: the top layer-the power layer-the stratum-the bottom layer. At this time, the model of the top level alignment characteristic impedance is a microstrip line model with the power supply plane as the reference plane. Will the addition of test points affect the quality of high-speed signals? As for whether it will affect the quality of the signal, it depends on how fast the test method and signal are. Basically, the additional test point(without the existing online perforation(via or DIP pin) as the test point) may be added to the line or pulled out of the line. The former is equivalent to adding a small capacitor on the line, and the latter is an additional branch. Both of these conditions will have a slight effect on the high-speed signal, and the degree of influence is related to the frequency speed of the signal and the rate of change of the signal edge. The impact can be known through simulation. In principle, the smaller the test point, the better(and of course the requirements of the test apparatus) the shorter the branch, the better. 12 How should the ground lines between the boards of several PCB components be connected? When the signals or power supplies between the various PCB boards are connected to each other during the action, for example, the A board has a power supply or a signal sent to the B board, there must be an equal amount of current flowing from the formation back to the A board(this is Kirchoff board law). The current on this layer will flow back where the impedance is minimal. Therefore, at each interface, whether the power supply or the signal is connected to each other, the number of tubes assigned to the formation must not be too small to reduce the impedance, which can reduce the noise on the formation. In addition, it is also possible to analyze the entire current loop, especially the part with a large current, and adjust the connection of the stratum or the ground line to control the current movement(for example, making a low impedance somewhere, allowing most of the current to go from this place), Reduce the impact on other more sensitive signals.
With the continuous improvement of human living environment, the environmental problems involved in the current PCB production process are particularly prominent. The topic of lead and bromine is the most popular, and lead-free and halogenated will affect the development of PCBs in many ways. Although at present, the changes in the surface treatment process of PCBs are not very large, it seems to be relatively distant, but it should be noted that long-term slow changes will lead to great changes. With the increasing demand for environmental protection, the surface treatment process of PCBs will surely undergo great changes in the future. The basic purpose of surface treatment is to ensure good weldability or electrical performance. Since natural copper tends to exist in the form of oxides in the air, it is unlikely to remain as raw copper for a long time, so other treatment of copper is required. Although most copper oxides can be removed using a strong flux in subsequent assembly, the strong flux itself is not easily removed, so strong flux is generally not used in the industry. There are many PCB surface treatment processes. The five processes that are common are hot wind leveling, organic coating, electroless nickel/gold immersion, silver immersion and tin immersion. The following are described one by one. 1, hot wind leveling(tin spray) Hot wind leveling, also known as hot wind solder leveling(commonly known as tin spray), is a process of coating melted tin(lead) solder on the surface of PCB and heating compressed air to flatten it to form a layer of both copper oxidation. It also provides a good weldable coating. The solder and copper form copper tin intermetallic compounds at the junction during thermal wind consolidation. PCB must sink in the molten solder during hot air consolidation; The wind knife flatten the liquid solder before the solder solidifies; The wind knife can minimize the meniscus of the solder on the copper surface and prevent the solder bridge. 2, organic weldable protective agent(OSP) OSP is a process that meets the requirements of the RoHS directive for the surface treatment of printed circuit board(PCB) copper foil. OSP is an abbreviation of Orgatic Solderability Preservice. It is translated as an organic-bonded film, also known as a copper-protecting agent, and English is also known as Preflux. Simply put, the OSP is a layer of organic skin film that grows chemically on a clean, bare copper surface. This film has anti-oxidation, heat resistance, and humidity resistance to protect the copper surface from further rust(oxidation or vulcanization, etc.) in normal environments; However, in the subsequent high temperature welding, this protective film must be easily removed by the flux so that the exposed clean copper surface can be immediately combined with the molten solder in a very short period of time to form a solid solder point. 3, whole plate nickel plating gold Nickel-plated gold is plated with nickel on the PCB surface conductor and then coated with gold. Nickel plating is mainly to prevent the diffusion between Jinhe copper. There are two types of electroplated nickel gold: plated soft gold(pure gold, gold surface does not look bright) and Plated hard gold(smooth and hard surface, wear resistance, containing other elements such as cobalt, gold surface looks brighter). Soft gold is mainly used for gold wire when chip packaging; Hard gold is mainly used for electrical interconnections at non-welding sites. 4, Shen Jin Shen Jin is a thick, well-charged nickel alloy wrapped on the copper surface, which can protect PCBs for a long time; In addition, it also has the tolerance to the environment that other surface treatment processes do not have. In addition, caving gold can also prevent the dissolution of copper, which will benefit lead-free assembly. 5, Shen Xi Since all solders are currently tin-based, the tin layer can match any type of solder. The caisson process can form flat copper tin intermetallic compounds, which makes caisson have the same good weldability as hot wind leveling without the headache of hot wind leveling. The tin board can not be stored for too long and must be assembled according to the order of the tin. 6, Shen Yin Between organic coating and electroless nickel/gold plating, the process is relatively simple and fast. Even if exposed to heat, humidity and pollution, silver can still maintain good weldability, but it will lose luster. Sediment silver does not have the good physical strength of electroless nickel/gold because there is no nickel under the silver layer. 7, chemical nickel Palladium gold Compared with gold, chemical nickel Palladium gold has an additional layer of Palladium between nickel and gold. Palladium can prevent corrosion caused by substitution reactions and is fully prepared for gold deposition. Gold is closely covered with Palladium to provide a good contact surface. http://www.pcbindex.com/ 8, electroplating hard gold In order to improve the wear resistance of the product, increase the number of inserts and draws and plating hard gold. With the higher and higher user requirements, more and more stringent environmental requirements, more and more surface treatment processes, in the end, the choice of the type of surface treatment process with development prospects, more versatile, it seems to be a bit dazzling, confusing. The future direction of the PCB surface treatment process can not be accurately predicted. In any case, meeting user requirements and protecting the environment must be done first!
Equipment Types In the production process of printed circuit boards, there are two main types of plating equipment, one is horizontal plating line and the other is vertical plating line. These two different types of electroplating equipment, mainly the way the board is transported, the structure of the transport board used is different, so it is slightly different for maintenance. Daily maintenance and maintenance methods 1. Maintenance and maintenance of the tank The main difference between the vertical plating line and the horizontal plating line is that the circuit board is transported differently, and the maintenance and maintenance methods for the tank are essentially the same. 7d should be cleaned once for each washing tank, clean it once and replace its bath; check the sprinkler in the tank to see if there is any blockage, and promptly clear the blockage. For the copper plating tank, the conductive support on the tin plating tank and the contact position between the anode and the fire wire, it can be wiped with a rag and sandpaper for cleaning and cleaning; for the copper plating tank, the tin basket of the tin plating tank, and the tin basket A check, replace the rotten titanium basket bag, tin bar basket, and add copper balls, tin bars, after adding copper balls and tin bars in 7d, electrolysis should be carried out on the electroplating copper tank and the electroplating tin bath. In 7d, high- and low-current methods are also used for trial production, so that after the newly added copper balls and tin bars are finished, the production performance is stabilized before production. The copper ball and anode bag should be cleaned once every 90. The bath is cleaned and cleaned once every 120~150 days with activated carbon. The impurities in the bath are filtered out and the tin bath is cleaned once. 2. Maintenance and maintenance of the vertical plating line vibration mechanism In the vertical plating, in order to ensure the uniformity of the surface copper and the effect of the hole copper during the plating, the board will be vibrated and oscillated, and there will be a vibration swing mechanism on the tank body. 30d should check the reducer to see if it is working properly, check its tightness; check the tightness of the vibration-mounted motor bolt; check the wear of the vibrating rubber. For the more serious wear, it should be replaced in time. 180d Check the contact condition of the power cord in the junction box, and tighten the joint loosely. The power cord that melts or ages the insulation of the wire should be replaced in time to ensure the insulation between the power cables. It is necessary to inspect all the bearings on the vibrating mechanism once, the last grease, and the bearings that are seriously worn out should be replaced in time. http://www.pcbindex.com/ 3, vertical plating line maintenance and maintenance of the vertical plating line is the use of driving, hanging tools to the board. The crane and the hanger should be cleaned once a week (the vehicle and the hanger are not disassembled), so that the appearance is kept clean and tidy. When cleaning, use a rag to clean it and sand it with sandpaper. 30d Perform a check on the hanger to check the damage of the hanger; perform a check and maintenance on the motor and reducer of the driving, and check the entire transmission to ensure its normal operation. 180d In-depth cleaning and maintenance of the driving and hanging tools, the hanging tools should be removed from the driving for cleaning. 4, horizontal plating line conveyor maintenance and maintenance level The plating device used in the plating line is a roller, which uses the rotation of the roller to continuously feed the board into each slot. Therefore, the maintenance of the horizontal plating line conveyor and the vertical plating line have Some different. 7d Clean the roller of the horizontal plating line once and clean the foreign matter adhering to the roller to ensure the surface of the plate is clean when the plate is transported; check the connector to check for looseness. Every 180d, the roller is inspected once, the roller is inspected for wear, and the worn roller is replaced in time to ensure that the card does not appear when the plate is transported; the transmission gear, the drive shaft and the entire transmission system are required. Conduct an inspection and make timely repairs to the problems that arise. 5. Maintenance and maintenance of the circulating filtration system 7d Check the filter cartridge of the circulating filtration system once to see if the filter cartridge is leaking. The filter cotton core should be cleaned or replaced every 10~15d. In 30d, the filter carbon core should be replaced to ensure the filtration quality and the flow rate of the filter; the filter pump should be cleaned once and the filter hood and filter of the air pump should be cleaned. 30d Check the contact condition of the power supply connector of the pump motor and find that the looseness should be tightened in time. If the wire is aging, replace the new wire to ensure good contact and safe insulation and protect the motor. 6. Maintenance and maintenance of other parts 7d It is necessary to check the output power of the power supply twice; it is necessary to check the power supply, electrical control heat dissipation and radiator, dust removal and cleaning to prevent it from affecting heat dissipation. 30d Check the electrical components of the electrical unit. If there is any damage or corrosion, it should be replaced in time. Check all the connectors. If there is contact, virtual connection and virtual welding, it should be repaired in time. If there is corrosion and damage, it should be replaced in time; Check each contactor and relay. If there is contact failure or contact sticking, replace it in time; check the main parameters of capacitors, reactors and resistors. If abnormality occurs, replace it as soon as possible. For the automatic feeding system, 7d should be checked and calibrated once. 7d should clean the scale and dirt on the electric heater to prevent the internal temperature of the electric heater from being too high. For each water and gas pipeline system, 7d will be inspected once to see if there is any running or leaking liquid phenomenon, and the pipelines with running and leaking liquid phenomena should be repaired and replaced in time. 2. Maintenance discussion before long-term shutdown If the equipment is planned to be shut down for a long time, it should be maintained so that it will not be subject to erosion and aging during the shutdown process. To clean the ground, wipe the water on the ground, and make the ground Keep dry and keep the machine, tank, driving and hanging equipment clean and dry; all motors are best protected with plastic wrap; all bearings are injected with grease for rust prevention; The syrup is completely cleaned; the syrup in the filter filter tank is cleaned; the filter filter is removed and cleaned; all the heaters in the tank should be cleaned to remove dirt and keep dry. Electroplating equipment for printed circuit board production applications, due to different manufacturing processes and different manufacturers, there will be some differences in equipment. Therefore, there will be some differences in maintenance methods, but the equipment must be timely and correct. Maintenance, must not neglect the maintenance and maintenance of the equipment due to the production schedule, production, only to ensure that the maintenance is correct and timely, in order to ensure the normal operation of the equipment, stable performance, to ensure the production and quality of production.
For a newly designed circuit board, debugging often encounters some difficulties, especially when the board is large and there are many components, it is often impossible to start. But if you master a reasonable set of debugging methods, debugging will be more effective. For the new PCB board that we just got back, we must first observe whether there are any problems on the board, such as whether there are obvious cracks, short circuit or open circuit. If necessary, check if the resistance between the power supply and the ground is large enough. Then there is the component installed. Modules that are independent of each other, if you are not sure that they are working properly, it is best not to install them all, but to install some of them (for smaller circuits, you can install them all at once), so that it is easy to determine the fault range. When you have problems when you are not getting it, you can't start. http://www.pcbindex.com/ In general, you can install the power supply first, and then power on to check if the power supply output voltage is normal. If you don't have much control when powering up (even if you have great confidence, it is recommended to add a fuse, just in case), consider using an adjustable regulated power supply with current limiting. First, preset the overcurrent protection current, then slowly increase the voltage value of the regulated power supply, and monitor the input current, input voltage, and output voltage. If there is no overcurrent protection and other problems during the upward adjustment, and the output voltage is also normal, the power supply is OK. Otherwise, disconnect the power supply, look for the point of failure, and repeat the above steps until the power is normal. Next, gradually install other modules. Each time a module is installed, it is powered on and tested. When powering up, follow the above steps to avoid over-current and burn out components due to design errors or/and installation errors. There are several ways to find faults: 1 measurement voltage method. The first thing to confirm is whether the voltage of each chip's power supply pin is normal, and then check whether the various reference voltages are normal, and whether the working voltage of each point is normal. For example, when a general silicon transistor is turned on, the BE junction voltage is about 0.7V, and the CE junction voltage is about 0.3V or less. If the BE junction voltage of a triode is greater than 0.7V (except for special triodes, such as Darlington), it may be that the BE junction is open. 2 signal injection method. Add the signal source to the input, and then measure the waveform of each point in turn to see if it is normal to find the fault point. Sometimes we will use a simpler method, such as holding a dice by hand, touching the input terminals of each level to see if there is any reaction at the output, which is often used in audio, video and other amplifier circuits (but note that the hot backplane This circuit cannot be used for circuits or circuits with high voltages, otherwise it may cause electric shock. If there is no reaction at the previous level and there is a reaction at the next level, the problem is at the previous level and should be checked. 3 Of course, there are many other ways to find fault points, such as watching, listening, smelling, touching, etc. "Look" is to see if the component has obvious mechanical damage, such as cracking, blackening, deformation, etc.; "listening" means listening to the working sound is normal, for example, something that should not ring, the sound is not ringing or sound Not normal; "smell" is to check for odor, such as the smell of burning, the taste of the capacitor electrolyte. For an experienced electronic maintenance person, these odors are very sensitive; "touch" is to test the temperature of the device by hand, such as too hot, or too cold. Some power devices will generate heat when they work. If they are cold, they can basically be judged that they are not working. But if the hot place is not hot or the hot place is too hot, it will not work. General power triodes, voltage regulator chips, etc., working below 70 degrees is completely ok. What is the concept of 70 degrees? If you put your hand on it, you can stick to it for more than three seconds, which means that the temperature is about 70 degrees (note that you should try it first, don't burn your hands).
Whether it is in the manufacturing assembly process or in actual use, it is essential that the PCB has reliable performance. In addition to the associated costs, defects in the assembly process may be carried into the final product by the PCB, and failure may occur during actual use, resulting in a claim. Therefore, from this point of view, it is no exaggeration to say that the cost of a good quality PCB is negligible. http://www.pcbindex.com/ In all market segments, especially those that produce products in critical applications, the consequences of such failures are unimaginable. These aspects should be kept in mind when comparing PCB prices. Although the initial cost of a reliable, guaranteed, and long-life product is high, it is worth the money in the long run. 14 most important features of high reliability boards 1, 25 micron hole wall copper thickness Benefits: Enhanced reliability, including improved z-axis resistance to expansion. Risk of not doing so Blowing or degassing, electrical connectivity problems during assembly (inner layer separation, hole wall fracture), or failure under load conditions in actual use. IPCClass2 (the standard used in most plants) requires 20% less copper plating. 2, no welding repair or open circuit repair Benefits: Perfect circuit ensures reliability and safety, no maintenance, no risk Risk of not doing so If it is not repaired properly, it will cause the board to open. Even if the repair is 'proper', there is a risk of failure under load conditions (vibration, etc.), which may cause malfunction in actual use. 3. Exceeding the cleanliness requirements of the IPC specification Benefits: Improve PCB cleanliness to increase reliability. Risk of not doing so Residues and solder deposits on the board pose a risk to the solder mask. Ion residues can cause corrosion and contamination risks on the solder surface, which can lead to reliability issues (bad solder joints/electrical faults) and ultimately increase the actual fault occurrence. Probability. 4. Strictly control the service life of each surface treatment Benefits: solderability, reliability, and reduced risk of moisture intrusion Risk of not doing so Due to metallographic changes in the surface treatment of old boards, soldering problems may occur, and moisture intrusion may cause delamination, separation of inner layers and walls (opening) during assembly and/or actual use. . 5. Use internationally renowned substrates – do not use “local” or unknown brands Benefits: Improve reliability and known performance Risk of not doing so Poor mechanical properties mean that the board does not perform as expected under assembly conditions. For example, high expansion performance can cause delamination, open circuit, and warpage problems. Impaired electrical characteristics can result in poor impedance performance. 6. Cladding tolerance meets IPC4101 Class B/L requirements Benefits: Strict control of the dielectric layer thickness can reduce the expected deviation of electrical performance. Risk of not doing so Electrical performance may not meet the specified requirements, and the output/performance of the same batch of components will vary greatly. 7. Define the solder mask material to ensure compliance with IPC-SM-840 ClassT requirements Benefits: NCAB Group recognizes “excellent” inks for ink safety and ensures solder mask inks meet UL standards. Risk of not doing so Inferior inks can cause adhesion, flux resistance and hardness problems. All of these problems can cause the solder mask to detach from the board and eventually lead to corrosion of the copper circuit. Poor insulation properties can cause short circuits due to unexpected electrical connectivity/arc. 8. Define tolerances for shapes, holes and other mechanical features Benefits: Strict control of tolerances can improve the dimensional quality of the product – improved fit, shape and function Risk of not doing so Problems during assembly, such as alignment/mating (the problem of press-fitting the needle is only found when the assembly is complete). In addition, there is a problem in mounting the base due to an increase in dimensional deviation. 9. NCAB specifies the thickness of the solder mask, although IPC has no relevant regulations. Benefits: Improve electrical insulation properties, reduce the risk of flaking or loss of adhesion, and strengthen the ability to withstand mechanical impact – no matter where the mechanical impact occurs! Risk of not doing so Thin solder masks can cause adhesion, flux resistance and hardness problems. All of these problems can cause the solder mask to detach from the board and eventually lead to corrosion of the copper circuit. Poor insulation properties due to the thin solder mask layer can cause short circuits due to accidental conduction/arc. 10. Define appearance requirements and repair requirements, although IPC is not defined Benefits: Care and careful care in the manufacturing process. Risk of not doing so A variety of scratches, minor injuries, repairs and repairs – the board can be used but not good looking. In addition to the problems that the surface can see, what are the invisible risks, the impact on assembly, and the risks in actual use? 11, the requirements for plug depth Benefit: High quality plug holes will reduce the risk of failure during assembly. Risk of not doing so The chemical residue in the immersion gold process may remain in the hole that is not filled with the plug hole, thereby causing problems such as solderability. Moreover, tin beads may be hidden in the holes, and the solder balls may splash out during assembly or actual use, causing a short circuit. 12, PetersSD2955 specified peelable blue plastic brand and model Benefit: The designation of peelable blue glue avoids the use of "local" or cheap brands. Risk of not doing so Inferior or inexpensive peelable glue may foam, melt, crack or solidify like concrete during assembly, so that the peelable glue cannot be peeled off/inactive. 13. NCAB performs specific approval and order procedures for each purchase order. Benefits: The execution of this program ensures that all specifications have been confirmed. Risk of not doing so If the product specifications are not carefully confirmed, the resulting deviation may not be discovered until assembly or final product, and it is too late. 14. Do not accept sets of boards with scrapped units Benefits: Failure to use partial assembly can help customers improve efficiency. Risk of not doing so A defective assembly requires special assembly procedures. If the x-out is not clearly marked or is not isolated from the panel, it is possible to assemble the known bad plate. Waste parts and time.
(1) Components are best placed on one side. If you need to place the components on both sides, place the pin components on the bottom layer (BottomLayer), and the components should be placed on one side. http://www.pcbindex.com/ It is possible that the circuit board is not easy to place and is not conducive to soldering. Therefore, it is preferable to place only the chip components on the bottom layer in the bottom layer (BottomLayer), similar to the component arrangement method on the common computer graphics card PCB board. When laying on one side, it is only necessary to make a silk screen on one side of the board to reduce the cost. (2) Reasonably arrange the position and orientation of the interface components. In general, connector components that are connected to the circuit board and the outside (power, signal lines) are usually placed at the edges of the board, such as serial ports and parallel ports. If placed in the center of the board, it is obviously not conducive to wiring, connector components, and may not be connected due to the obstruction of other components. In addition, pay attention to the direction of the interface when placing the interface, so that the connection line can be additionally taken out when the interface is placed, away from the circuit board. After the interface is placed, you should use the String (string) of the interface component to clearly indicate the type of interface; for the power class interface, the voltage level should be marked to prevent the board from burning due to wiring errors. (3) It is better to have a wide electrical isolation between the high-voltage components and the low-voltage components. In other words, do not make the voltage levels vary greatly. It is better to have a wide electrical isolation between the high-voltage components and the low-voltage components. Do not place components with widely different voltage levels, which is beneficial to electrical insulation and has great benefits for signal isolation and interference immunity. (4) Components with close electrical connections are best placed together. This is the modular layout idea. (5) For components that are prone to noise, such as clock generators and crystal oscillators, high frequency devices such as clock generators and crystal oscillators should be placed as far as possible at the clock input. High-current circuits and switching circuits are also prone to noise. In the layout, these components or modules should also be away from high-speed signal circuits such as logic control circuits and storage circuits. If possible, use control boards in conjunction with power boards. To connect, to improve the overall anti-interference ability and reliability of the circuit board. (6) Place decoupling capacitors and filter capacitors around the power supply and chip as much as possible. The arrangement of decoupling capacitors and filter capacitors is an important measure to improve the power quality of the board and improve the anti-interference ability. In practical applications, traces, pin connections, and wiring of printed circuit boards may cause large parasitic inductance in practical applications, resulting in high-frequency ripple and glitch in power waveforms and signal waveforms. Placement between the power supply and ground can cause large parasitic inductance, resulting in high frequency ripple and glitch in the power supply waveform and signal waveform. A 0.1F decoupling capacitor decoupling capacitor can effectively filter out these high frequencies. Ripple and burrs. If a chip capacitor is used on the board, the chip capacitor should be placed close to the component's power supply pin. For power conversion chips, or power inputs, it is best to place a 10F or larger capacitor to further improve power quality. (7) The component number should be placed close to the frame of the component, the size is uniform, the direction is neat, and it does not overlap with the components, vias and pads. The first pin of the component or connector indicates the direction; the signs of the positive and negative electrodes should be clearly marked on the PCB and must not be covered; the power conversion component power conversion components (such as DC/DC converter, linear conversion power supply) And the switching power supply should have enough heat dissipation space and installation space, and there is enough welding space on the periphery.