Divided into rigid circuit boards and flexible circuit boards, soft and hard combination of boards. Generally, the PCB shown in the first picture below is called Rigid PCB, and the yellow connecting line in the second picture is called Flexible PCB. the intuitive difference between Rigid PCB and Flexible PCB is that Flexible PCB can be bent. Rigid PCB common thickness of 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.6mm, 2.0mm and so on. The common thickness of flexible PCB is 0.2mm, where parts are to be soldered, a thicker layer is added behind it, and the thickness of the thicker layer varies from 0.2mm to 0.4mm. The purpose of knowing this is to provide structural engineers with a space reference when designing. Rigid PCB materials include: phenolic paper laminates, epoxy paper laminates, polyester glass mat laminates, epoxy glass cloth laminates; Flexible PCB materials include: polyester film, polyimide film, fluorinated ethylene propylene film.
Raw materials
Copper-clad laminate is the substrate material for printed circuit boards. It is used as a support for various components and enables electrical connection or insulation between them.
Aluminum substrate
PCB aluminum substrate (metal-based heat sinks including aluminum substrate, copper substrate, iron substrate) is a low-alloyed Al-Mg-Si system of high-plasticity alloy plate (structure see the figure below), which has a good thermal conductivity, electrical insulation and machining properties, the mainstream aluminum substrate Foslite.
Junction Processing
The soldermask covers most of the copper side of the circuit, exposing only the termination point for soldering of parts, electrical testing, and circuit board insertion. The terminals require an additional layer of protection to prevent oxidization of the anode (+) terminals during long-term use, which can affect circuit stability and pose safety concerns.
Electroplated hard gold plating on the circuit board plug endpoints (commonly known as gold fingers) plated with a layer of nickel and high chemical passivity of the gold layer to protect the endpoints and provide good connectivity, which contains an appropriate amount of cobalt, with excellent wear characteristics.
Tin-spraying covers the soldered ends of the board with a layer of tin-lead alloy in a hot-air leveling process to protect the board ends and provide good solderability.
Pre-soldering covers the soldered ends of the boards with a layer of antioxidant pre-soldering film by dipping, temporarily protecting the soldered ends before soldering and providing a more flat surface for better soldering performance.
Carbon ink is printed on the contact points of the board by screen printing to protect the end points and provide good connectivity.
Forming and Cutting
Circuit boards are cut to customer specifications using CNC molding machines (or die presses). During the cutting process, the circuit board is fixed to the bed (or mold) with pins through previously drilled holes. After cutting, the gold fingers are beveled to facilitate the insertion of the board. For multi-chip circuit boards, an X-shaped break line (known in the industry as a V-Cut) is often required to facilitate the customer to split and disassemble the board after insertion. Finally, the board is cleaned of dust and surface ionic contaminants.
Final Inspection and Packaging
Before packaging, the circuit boards undergo a final electrical conduction and impedance test, as well as a solderability and thermal shock resistance test. The board is then baked to eliminate moisture and heat stress during the manufacturing process, and finally packaged in a vacuum bag for shipment.
Production Electronic hobbyist PCB production methods are mainly thermal transfer method, photosensitive wet film method, photosensitive dry film method. Etching agents are environmentally friendly ferric chloride (FeCl3), there are fast hydrochloric acid plus hydrogen peroxide (HCl + H2O2). Commonly used PCB drawing software such as Altium Designer 10 Altium Designer (formerly known as Protel) series software. Photographic dry film + ferric chloride is the best first choice for hobbyists Imaging (forming / lead generation)
The first step in the production is to build out the wiring of the inter-part online. We use a Subtractive transfer to represent the working negative on a metal conductor. This technique involves laying a thin layer of copper foil over the entire surface and eliminating the excess. Additive Pattern transfer is another lesser-used method, which involves applying copper wire only where it is needed, but we won't go into that here.
Copper foil is laid on both sides of the PCB's substrate if it's being made as a double-sided board, or glued together in the next step if it's being made as a multilayer board.
Positive photoresist, which is made from a photoconductor, dissolves under illumination (negative photoresist breaks down if it is not illuminated). There are a number of ways to treat photoresist on copper surfaces, but the most common way is to heat it up and roll it over the surface containing the photoresist (called dry film photoresist). It can also be sprayed on in liquid form, although the dry-film style offers higher resolution and allows for finer wires to be made.
The photoresist is simply a template for the PCB layer in fabrication. Before the photoresist on the PCB is exposed to UV light, the mask covering it prevents some areas of the photoresist from being exposed (assuming a positive photoresist is used). These areas covered by the photoresist will become wiring.
After the photoresist is developed, the rest of the bare copper is etched. The etching process can be done by immersing the board in an etching solvent or by spraying the solvent on the board. Generally used as etching solvents, Ferric Chloride (Ferric Chloride), Alkaline Ammonia (Alkaline Ammonia), Sulfuric Acid + Hydrogen Peroxide (Sulfuric Acid + Hydrogen Peroxide), and Copper Chloride (Cupric Chloride), etc. through the oxidation of the oxidation reaction (e.g., Cu+, 2FeCl3 = Cu+). 2FeCl3=CuCl2+2FeCl2). After etching, the remaining photoresist is removed. This is called the Stripping procedure.
Drilling and plating
If you are making a multilayer PCB with buried or blind vias, each layer must be drilled and plated before bonding. Without this step, there is no way to connect them to each other.
After the holes are drilled by the machine according to the drilling requirements, the inside of the hole must be plated (Plated-Through-Hole technology, PTH). Plated-Through-Hole technology (PTH) is a metal treatment on the inside of the hole, which allows the internal layers of wiring to be connected to each other. Before plating is started, it is necessary to remove debris from the hole. This is because the resin epoxy produces some chemical changes when heated, and it will cover the internal PCB layer, so it must be removed first. Both the removal and plating actions will be done in the chemical process.
Multilayer PCB lamination
Multilayer boards are created by laminating individual layers. Pressing involves adding insulation between the layers and gluing them to each other. If there are vias through several layers, the process must be repeated for each layer. The wiring on the outside faces of the multilayer board is usually handled after the multilayer board is pressed together.
Processing the soldermask, stencil print surface, and gold finger plating
The soldermask is then applied to the outermost layer of the wiring so that the wiring does not come into contact with the outside of the plating. A screen print is applied to mark the location of the parts. It should not be applied to any wires or gold fingers, as this may reduce solderability or the stability of the current connection. The gold fingers are usually gold plated to ensure a high quality current connection when plugging into expansion slots.
Testing
To test a PCB for shorts or breaks, either optical or electronic testing can be used. Optical testing uses scanning to find defects in each layer, while electronic testing typically uses a Flying-Probe to check all connections. Electronic testing is more accurate at finding shorts or breaks, but optical testing makes it easier to detect problems with incorrect gaps between conductors.
Mounting and Soldering Parts
The final step is to mount and solder the parts. Both THT and SMT parts are mounted on the PCB using machines and equipment.
THT parts are usually soldered using a method called Wave Soldering. This allows all the parts to be soldered to the PCB in one pass, first cutting the pins close to the board and bending them slightly to allow the parts to be held in place. Next, the PCB is moved to a wave of flux, where the underside is exposed to the flux, which removes any oxides from the metal on the underside. After heating the PCB, this time it is moved to the melted solder, and after contact with the bottom, the soldering is complete.
Automatic soldering of SMT parts is called reflow soldering (Over Reflow Soldering). Inside the paste containing flux and solder solder in the parts mounted on the PCB after the first treatment, after the PCB is heated and then processed again. After the PCB cools, the soldering is complete, and the PCB is ready for final testing.
Proofing
PCB's Chinese name for the printed circuit board also known as printed circuit boards, printed circuit boards are important electronic components is the support body of electronic components? Is the provider of the electrical connection of electronic components. Because it is the use of electronic printing technology production is called "printed" circuit board.
PCB proofing is the printed circuit board in mass production before the trial production of the main application for electronic engineers in the design of the circuit? And after completing the PCB Layout to the factory for small batch trial production process that is PCB proofing. PCB proofing of the number of production is generally no specific boundaries are generally engineers in the product design is not completed before the confirmation and completion of the test are called PCB proofing.
Component layout
PCB layout process, the system layout is completed, we must review the PCB chart to see if the system layout is reasonable, whether to achieve the best results. Usually can be examined from the following aspects:
1. System layout to ensure that the wiring is reasonable or optimal, whether to ensure that the wiring is reliable, whether to ensure the reliability of the circuit work. In the layout of the signal direction as well as power and ground networks need to have an overall understanding and planning.
2. Whether the size of the printed circuit board and processing drawings in line with the size, can meet the PCB manufacturing process requirements, there is no behavioral marking. This point requires special attention, many PCB circuit layout and wiring are designed to be very beautiful, reasonable, but neglected to locate the precise positioning of the connectors, resulting in the design of the circuit can not be docked with other circuits.
3. Components in two-dimensional, three-dimensional space, there is no conflict. Note the actual size of the device, especially the height of the device. In the soldering-free layout of the component, the height of the general can not exceed 3mm.
4. Whether the component layout is sparse, well-organized, neatly arranged, whether all the cloth. In the layout of components, not only to consider the direction of the signal and the type of signal, the need to pay attention to or protection of the place, but also to consider the overall density of the device layout, so that the sparse and dense uniform.
5. Components that need to be replaced frequently can be easily replaced, plug-in board inserted into the device is convenient. Should ensure that the replacement of frequently replaced components and insertion of convenient and reliable.
6. Layout of the RF part of the special attention should be paid to avoid RF interference with other components, so one side must be done to isolate.
Design
Whether it is a single-panel, double-sided boards, multilayer board design, before the protel design out of the existing design with Altium Designer (formerly known as protel), PADS, Allegro and so on.
The design of printed circuit boards is based on the schematic diagram of the circuit to realize the functions required by the circuit designer. The design of printed circuit boards mainly refers to layout design, which requires consideration of various factors such as layout of external connections, optimized layout of internal electronic components, optimized layout of metal connecting lines and through-holes, electromagnetic protection, and heat dissipation. Excellent layout design can save production cost and achieve good circuit performance and heat dissipation performance. Simple layout designs can be realized manually, while complex layout designs need to be realized with the help of computer-aided design (CAD).
1 Overview
The purpose of this document is to illustrate the process of printed board design using PowerPCB, the printed board design software of PADS, and some considerations, to provide design specifications for a workgroup of designers, and to facilitate communication and mutual checking between designers.
2 Design flow
The design flow of PCB is divided into six steps: netlist input, rule setting, component layout, routing, checking, reviewing, and output.
2.1 Netlist Input
There are two ways to input the netlist, one is to use PowerLogic's OLE PowerPCB Connection function, select Send Netlist, and apply the OLE function, which can keep the schematic and PCB diagrams consistent at all times to minimize the possibility of errors. Another method is to load the netlist directly in PowerPCB, select File->Import, and enter the netlist generated from the schematic.
2.2 Rule Setting
If you have already set up the design rules for the PCB during the schematic design phase, you don't need to set up these rules again because the design rules have already been entered into PowerPCB along with the netlist when you enter the netlist. If the design rules are modified, the schematic must be synchronized to ensure that the schematic and PCB are consistent. In addition to the design rules and layer definitions, there are some rules that need to be set, such as Pad Stacks, which require modification of the size of the standard vias. If the designer creates a new pad or vias, be sure to add Layer 25.
Note:
PCB design rules, layer definitions, vias setup, CAM output settings have been made into a default startup file, the name of which is Default.stp, the netlist is inputted in and then, in accordance with the actual design of the power supply network and the ground are assigned to the power supply and ground layers, and other advanced rules are set. ground layer, and set other advanced rules. After all the rules are set up, in PowerLogic, use the Rules From PCB function of OLE PowerPCB Connection to update the rule settings in the schematic to ensure that the rules in the schematic and PCB are consistent.
2.3 Component Layout
After the netlist is entered, all the components will be placed at the zero point of the workspace, overlapping together, and the next step is to separate these components and arrange them neatly according to some rules, i.e., component layout.PowerPCB provides two methods, manual layout and automatic layout.
2.3.1 Manual Layout
1. Tools printed circuit board structure dimensions drawn board edge (Board Outline).
2. Disperse Components, which are arranged around the board edge.
3. Move and rotate the components one by one, put them inside the board edge, and arrange them neatly according to certain rules.
2.3.2 Auto Layout
PowerPCB provides Auto Layout and Auto Local Cluster Layout, but it is not ideal for most designs and is not recommended.
2.3.3 Precautions
a. The first principle of layout is to ensure that the wiring of the cloth through the rate of attention to the flying wires when moving the device to connect the devices that have a relationship with the wiring together
b. digital and analog devices should be separated, as far as possible away from the
c. decoupling capacitors as close as possible to the device's VCC
d. Place the device When placing devices, consider soldering them later, not too dense
e. Use the Array and Union functions provided by the software to improve the efficiency of the layout
2.4 Wiring
There are also two types of wiring methods, manual wiring and automatic wiring. DRC), and automatic wiring is performed by Specctra's wiring engine. Usually these two methods are used in conjunction with each other, and the common steps are manual-automatic-manual.
2.4.1 Manual wiring
1. Before the automatic wiring, the first manual cloth some important networks, such as high-frequency clock, main power supply, etc., these networks often have special requirements for the alignment distance, line width, line spacing, shielding, and so on; in addition, some special packages, such as the BGA,
Automatic cloth is very difficult to cloth the rules, but also to use the manual wiring.
2. After the automatic wiring, but also with manual wiring to adjust the PCB alignment.
2.4.2 Automatic wiring
After the manual wiring is finished, the rest of the network is left to the autowireer to self-route. Select Tools->SPECCTRA, start the Specctra wiring interface, set up the DO file, press Continue to start the Specctra wiring automatically wiring the Specctra wiring device, after the end of the cloth through the rate of 100%, then you can manually adjust the wiring; if less than 100%, that the layout or manual wiring has problems, you need to Adjust the layout or manual wiring until all through.
2.4.3 Precautions
a. Thicken the power and ground wires as much as possible
b. Connect the decoupling capacitor directly to VCC as much as possible
c. When you set up Specctra's DO file, add the Protect all wires command first to protect the wires that have been manually routed from being rewired by the autowireer
d . . If there is a mixed power layer, you should define the layer as a Split/mixed Plane, split it before wiring, and then use Plane Connect of Pour Manager to overlay the wires after wiring
e. Set all device pins to the hot-pad method by setting Filter to Pins, checking all the Pins,
modify the properties, and tick the box in front of Thermal option
f. Turn on the DRC option when manually routing the device, and use Dynamic Route
2.5 Inspection
The items to be inspected are Clearance, Connectivity, High Speed, and Power Supply Rule. Rules (High Speed) and Power Layer (Plane), which can be done by selecting Tools->Verify Design. If the High Speed rule is set, it must be checked, otherwise this item can be skipped. Check out the error, you must modify the layout and wiring.
Note:
Some errors can be ignored, for example, some connectors Outline part of the Outline is placed outside the board frame, check the spacing will be wrong; in addition, each time after the modification of the alignment and over the holes, it is necessary to re-copper once.
2.6 Review
Review according to the "PCB checklist", including design rules, layer definition, line width, spacing, pads, hole settings; but also focus on reviewing the rationality of the layout of the device, power supply, ground network alignment, high-speed clock network alignment and shielding, decoupling capacitor placement and connection. Connection. Review failed, the designer to modify the layout and wiring, qualified, reviewers and designers signed respectively.
2.7 Design Output
PCB design can be output to the printer or output light drawing files. The printer can print the PCB in layers for the designer and the reviewer to check; the light drawing file to the board manufacturer, the production of printed circuit boards. Light drawing file output is very important, related to the success or failure of the design, the following will focus on the output of light drawing file notes.
a. Layers to be output are wiring layer (including the top layer, bottom layer, middle wiring layer), power supply layer (including the VCC layer and GND layer), silkscreen layer (including the top layer silkscreen, bottom layer silkscreen), soldermask layer (including the top layer soldermask and the bottom layer soldermask), in addition to generating drill files (NC Drill)
b. If the power supply layer is set to Split/Mixed, then in the Add Document Add Document, you will see the following information. Mixed, then select Routing for the Document item in the Add Document window, and use Pour Manager's Plane Connect to overlay copper on the PCB drawing before outputting the light drawing file each time; if it is set to CAM Plane, then select Plane, and when setting the Layer item, to Add Layer25, and select Pads and Vias in Layer25
c. In the Device Setup window (press Device Setup), change the value of Aperture to 199
d. Select Board Outline when setting the Layer of each layer
e. When setting the Layer of the silk screen layer, do not select Pads. When setting the Layer of silkscreen layer, do not select the Part Type, select the Outline, Text, and Line of the top layer (bottom layer) and silkscreen layer
f. When setting the Layer of soldermask layer, selecting the Over Hole means that there is no soldermask on the over-hole, and not selecting the Over Hole means that there is no soldermask on the house, depending on the situation
g. When generating the hole file, use the default settings of the PowerPCB default settings, do not make any changes
h. After the output of all the light drawing files, open with CAM350 and print, by the designer and reviewers according to the "PCB checklist" check.