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What is the difference between positive and negative PCBs 1. The difference between positive and negative PCBs: PCB positive and negative are manufacturing processes with opposite final effects. The effect of PCB positive: The copper on the printed board is retained in areas where lines are drawn, and the copper on areas where no lines are drawn is removed. The signal layer, such as the top and bottom layers, is the positive. The effect of PCB negative film: The copper coating on the printed board is removed in areas where lines are drawn, while the copper coating is retained in areas where no lines are drawn. The Internal Planes layer (referred to as the Internal Planes layer) is used to arrange power and ground wires. The wiring or other objects placed on these layers are copper free areas, meaning that this working layer is negative. 2. What are the differences between PCB positive and negative output processes? Negative film: Generally, it is the tenting process that we ref
PCB interference is mainly divided into two types. One type comes from within the PCB, mainly due to the influence of parasitic coupling between adjacent circuits and field coupling of internal components, resulting in signal crosstalk along the transmission path. For example, capacitors on PCBs, especially those used in high-frequency situations. We can consider it as an LCR circuit, because when a capacitor actually works in a circuit, it generally produces equivalent inductance and impedance, and the capacitor has a self resonant frequency. At the self resonant frequency, the capacitor exhibits capacitance. When the frequency is higher than the self resonant frequency, the capacitance appears inductive, and the impedance increases with the increase of frequency. Another type of electromagnetic interference comes from the outside of the PCB, which is further divided into two types: radiation interference and sensitive element problems. Radiation mainly comes from harmonic sources
In terms of layout, when the circuit board size is too large, although welding is easier to control, the printed lines are longer, the impedance increases, the noise resistance decreases, and the cost increases; If it is too small, the heat dissipation will decrease, and welding will be difficult to control, making it easy for adjacent lines to interfere with each other, such as electromagnetic interference from circuit boards. Therefore, it is necessary to optimize the PCB board design: (1) Shorten the connection between high-frequency components and reduce EMI interference. (2) Components with heavy weight (such as exceeding 20g) should be fixed with brackets and then welded. (3) Heating elements should consider heat dissipation issues to prevent significant surface damage to the components Δ Defects and rework caused by T should keep the thermistor away from the heat source. (4) The arrangement of components should be as parallel as possible, which is not only aesthetically
The basic requirement for etching quality is to be able to completely remove all copper layers except below the corrosion-resistant layer, that's all. Strictly speaking, if we want to define it accurately, the etching quality must include the consistency of wire width and the degree of lateral corrosion. Due to the inherent characteristics of the current corrosive solution, it not only causes etching in the downward direction but also in both the left and right directions, so lateral corrosion is almost inevitable. The side etching problem is a frequently discussed aspect of etching parameters, defined as the ratio of side etching width to etching depth, known as the etching factor. In the printed circuit industry, its range of variation is very broad, from 1:1 to 1:5. Obviously, a small etching degree or low etching factor is the most satisfactory. The structure of the etching equipment and the different components of the etching solution will have an impact on the etching facto
It should be noted that there are two layers of copper on the board during etching. In the outer etching process, only one layer of copper must be completely etched off, while the rest will form the final required circuit. This type of graphic electroplating is characterized by the copper plating layer only existing below the lead tin corrosion-resistant layer. Another process method is to plating copper on the entire board, with only tin or lead tin corrosion-resistant layer on the outer part of the photosensitive film. This process is called "full plate copper plating process". Compared with graphic electroplating, the biggest drawback of full plate copper plating is that copper must be plated twice on all parts of the board, and they must also be corroded off during etching. Therefore, when the wire width is very fine, a series of problems will occur. At the same time, side corrosion will seriously affect the uniformity of the lines. In the processing technology of the outer c
Activation and copper deposition are key processes in the process of pore metallization in chemical plating. Although qualitative and quantitative analysis of ion palladium and reducing solution can reflect the activation and reduction performance, their reliability is not comparable to that of glass cloth tests. The most stringent conditions for copper deposition on glass cloth can best demonstrate the performance of activation, reduction, and copper deposition solution. The current introduction is as follows: (1) Material: Deslur the glass cloth in a 10% sodium hydroxide solution. And cut it into 50 x 50 (mm), remove some glass fibers from the ends around it, and let the glass fibers scatter. (2) Test steps: A. Treat the sample according to the copper deposition process procedure; B. Put it into the copper plating solution, and after 10 seconds, the end of the glass cloth should be completely coated with copper, appearing black or dark brown. After 2 minutes, all should be coat
Before through-hole plating, the copper foil is subjected to micro etching treatment to roughen the microstructure and increase the adhesion with the deposited copper layer. To ensure the stability of the etching solution and the uniformity of copper foil etching, it is necessary to measure the etching rate to ensure it is within the specified range of the process. (1) Material: 0.3mm copper foil plate, degreased, brushed, and cut into 100 x 100 (mm); (2) Measurement procedure: A. The sample is corroded in hydrogen peroxide (80-100 g/L) and sulfuric acid (160-210 g/L) at a temperature of 30 ℃ for 2 minutes, and then cleaned with deionized water; B. Bake at 120-140 ℃ for 1 hour, weigh W2 (g) at constant weight, and weigh W1 (g) at constant weight before corrosion. (3) Etching rate calculation rate=(W1-W2) 104/2 x 8.933T( μ M/min) In the formula: s - sample area (cm2) T - etching time (min) (4) Judgment: 1-2 μ The corrosion rate of m/min is appropriate. (Corrosion of copper 270-
What are the key points in PCB design? 1. Select PCB board The selection of PCB boards must strike a balance between meeting design requirements and achieving mass production and cost. The design requirements include two parts: electrical and mechanical. This material issue is usually important when designing very high-speed PCB boards (frequencies greater than GHz). For example, the commonly used FR-4 material may not be suitable as its dielectric loss at several GHz frequencies can have a significant impact on signal attenuation. In terms of electrical performance, attention should be paid to whether the dielectric constant and dielectric loss are used together at the designed frequency. 2. Avoiding high-frequency interference The basic idea to avoid high-frequency interference is to minimize the interference of high-frequency signal electromagnetic fields, also known as crosstalk. You can widen the distance between the high-speed signal and the analog signal, or add ground gua
In the electroplating process, it is common to have poor adhesion when spraying paint on the coating, which is due to the presence of oil stains on the surface after electroplating. However, during the electroplating of parts, pinholes often occur after plating. Today, we will talk about pinholes caused by improper pre-treatment and the corresponding solutions. Frequently asked questions: (1) Parts that are not thoroughly degreased or stored improperly during machining may have dust falling on the surface. If left for a long time, the dust and grease may mix together, making it difficult to remove them completely, resulting in inconspicuous small oil spots. During plating, bubbles may remain on them, forming pinholes. (2) When polishing parts, abrasives, polishing paste, etc. are embedded in micro pits on the surface, which are difficult to clean and cannot deposit the coating, resulting in pinholes. (3) Incomplete or prolonged pickling of components may result in corrosion, wi
PCB board surface treatment PCB board surface treatment: oxidation resistance, tin spraying, lead-free tin spraying, gold sinking, tin sinking, silver sinking, hard gold plating, full board gold plating, gold finger, nickel palladium OSP: low cost, good solderability, strict storage conditions, short time, environmentally friendly process, good welding, and flatness. Tin spraying: Tin spraying boards are generally multi-layer (4-46 layers) high-precision PCB templates, which have been used by many large domestic communication, computer, medical equipment, aerospace enterprises and research units. The connecting finger is a connecting component between the memory module and the memory slot, and all signals are transmitted through the connecting finger. The golden finger is composed of numerous golden conductive contacts, and is called the "golden finger" because its surface is gold-plated and the conductive contacts are arranged like fingers. The golden finger is actually coated wi
As the integration level of ICs increases, the number of IC pins also increases. However, the vertical tin spraying process is difficult to blow flat the fine solder pads, which brings difficulty to SMT mounting; In addition, the shelf life of tin spray boards is very short. And the gold-plated plate precisely solves these problems: 1. For surface mount technology, especially for 0603 and 0402 ultra small surface mount, the flatness of the solder pads directly affects the quality of the solder paste printing process and has a decisive impact on the quality of subsequent reflow soldering. Therefore, whole board gold plating is often seen in high-density and ultra small surface mount processes. 2. In the trial production stage, the influence of factors such as component procurement is often not that the board is soldered immediately upon arrival, but that it often has to wait for several weeks or even months before use. The shelf life of gold-plated boards is many times longer than
The significance and design difficulties of PCB copper coating The significance of copper coating is to reduce the impedance of the ground wire and improve its anti-interference ability; Reduce voltage drop and improve power efficiency; Connected to the ground wire, it can also reduce the loop area. For the purpose of minimizing deformation during PCB soldering, most PCB manufacturers also require PCB designers to fill open areas with copper sheets or grid like ground wires. If copper plating is not handled properly, it will not be worth the loss. Is copper plating "more beneficial than harmful" or "more harmful than beneficial"? Everyone knows that in high-frequency situations, the distributed capacitance of the wiring on the printed circuit board will play a role. When the length is greater than 1/20 of the corresponding wavelength of the noise frequency, an antenna effect will be generated, and noise will be emitted outward through the wiring. If there is a poorly grounded coppe
Complete Collection of PCB Failure Analysis Technologies 1. Appearance inspection Appearance inspection is the visual inspection or use of some simple instruments, such as stereomicroscope, metallographic microscope, or even magnifying glass, to examine the appearance of a PCB, find the location of failure and related physical evidence. Its main function is to locate the failure and preliminarily determine the failure mode of the PCB. The appearance inspection mainly checks the contamination, corrosion, location of bursting boards, circuit wiring, and regularity of failure of PCBs. If it is a batch or individual, whether it is always concentrated in a certain area, etc. In addition, many PCBs fail only after being assembled into PCBA, and it is necessary to carefully examine the characteristics of the failure area to determine whether it is caused by the influence of the assembly process and the materials used in the process. 2. X-ray fluoroscopy examination For certain areas tha
During the processing of PCB circuit boards, it is inevitable to encounter several defective products, which may be caused by machine errors or human factors. For example, sometimes there may be an abnormal situation called hole breakage, and the cause needs to be analyzed in detail. If the state of hole breakage is a point like distribution rather than a complete circuit breaking phenomenon, it is called point like hole breakage, and some people also call it "wedge shaped hole breakage". The common causes are due to poor processing of the adhesive residue removal process. During the PCB circuit board processing, the process of removing adhesive residue will first undergo a loosening agent treatment, followed by a strong oxidizing agent "permanganate" erosion operation. This process will remove adhesive residue and produce microporous structures. After the removal process, the remaining oxidant is removed by reducing agents, and a typical formula uses acidic liquid treatment. Due
Making a PCB board is not simply about following the process to complete the board. Just drill a hole and add the components. The production of PCBs is not difficult, but the difficulty lies in troubleshooting after completion. Whether it's a personal enthusiast or an industry engineer, encountering problems while debugging PCB circuit boards can be quite a headache, just like programmers encountering bugs. Some people have a strong interest in debugging PCB circuit boards, just like programmers solving bugs. There are many common PCB circuit board problems, including circuit board design, damage to electronic components, short circuits, component quality, and PCB circuit board wire breakage. The common PCB circuit board faults are mainly concentrated on components such as capacitors, resistors, inductors, diodes, transistors, field-effect transistors, etc. The obvious damage to integrated chips and crystal oscillators can be visually observed to determine the faults of these com
PCB sinking gold plate vs gold-plated plate In fact, there are two types of gold plating processes: electroplating gold and sinking gold. For the gold plating process, the effect of tin plating is greatly reduced, while the effect of tin plating on sinking gold is relatively better; Unless the manufacturer requires binding, most manufacturers now choose the sinking gold process! In general, the surface treatment of PCBs can be divided into the following types: gold plating (electroplating gold, sinking gold), silver plating, OSP, tin spraying (with and without lead). These are mainly aimed at FR-4 or CEM-3 boards, and paper substrates also have surface treatment methods coated with rosin; If we exclude the production and material process reasons of solder paste and other SMT manufacturers, we can discuss the issue of poor soldering (poor soldering). Here, we will only address the PCB issue, and there are several reasons for this: 1. During PCB printing, is there an oil leakage fi
Common problems and solutions for alkaline etching of circuit boards 1. Problem: Decreased etching rate in printed circuits Reason: Caused by improper control of process parameters Solution: Inspect and adjust process parameters such as temperature, spray pressure, solution density, pH value, and ammonium chloride content to the specified values according to process requirements. 2. Problem: Deposition of etching solution in printed circuits Reason: (1) The ammonia content is too low (2) Excessive water dilution (3) The specific gravity of the solution is too high Solution: (1) Adjust the pH value to reach the process specified value or appropriately reduce the exhaust volume. (2) Strictly follow the process requirements or reduce the exhaust volume appropriately during adjustment. (3) According to the process requirements, a portion of the solution with high specific gravity is discharged and analyzed, and then an aqueous solution of ammonium chloride and ammonia is ad
PCB causes some factors of poor surface quality 1. Substrate processing problems: Especially for some thinner substrates (generally below 0.8mm), because the substrate rigidity is poor, it is not appropriate to brush the board. This sample may not be able to effectively remove the protective layer specially treated to prevent the oxidation of copper foil on the surface of the substrate during the production and processing process, although the layer is thin and the brush board is easier to remove, but the chemical treatment is more difficult, so it is important to pay attention to control in the production and processing, so as to avoid the foaming problem caused by the poor bonding force between the copper foil on the substrate and the chemical copper; When this problem is blackened in the thin inner layer, there will also be poor blackening and Browning, uneven color, and poor local blackening and Browning. 2. Poor surface treatment caused by oil or other liquids contaminated w
Comparison of gold-plated and gold-plated circuit boards 1. The whole plate is gold-plated Generally refers to [electroplated] [electroplated nickel gold plate], [electrolytic gold], [electric gold], [electric nickel gold plate], there is a distinction between soft gold and hard gold (generally used as gold finger). The principle is to dissolve nickel and gold (commonly known as gold salt) in the chemical solution, the circuit board is immersed in the electroplating cylinder and the current is passed on the copper foil surface of the circuit board to generate nickel gold coating, electric nickel gold because of its coating hardness is high, wear resistance, not easy to oxidize the characteristics of electronic products have been widely used. Two, sinking gold Through the chemical REDOX reaction method to generate a layer of coating, generally thicker, is a kind of chemical nickel gold deposit method, can reach a thicker gold layer, usually called precipitation gold. Three, gold-
The reasons for the hole deviation are as follows: 1, there are pits on the cover plate, do not use aluminum plate with creases. 2, there are foreign bodies on the board, please pay attention to clean the board. 3, vacuum is not enough, please pay attention to vacuum negative pressure. 4. Drill The offset hole is irregular, so it is not a problem of positioning, film and material expansion and contraction, and it is a small offset hole, and the large hole in the middle is not offset. So there are basically a few things to check: 1. Whether the press foot of the rig is smooth. 2. The quality of the upper and lower backing plate, especially whether the upper backing plate is uneven. 3, whether the drill parameters are correct, 4. You are using a welding type of inferior drill. Generally, the above situation is basically the quality and parameters of the drill bit. Cheap drill bits of the Taiwanese type have more such problems. Germany, the United States, China, this kind of pr
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