With the increasingly complex design and application of electronic products, the performance specifications of integrated processors, memories and other key components have been greatly improved. To test the technical level of circuit board design carrying electronic components, it is necessary not only to meet the requirements of high density and high efficiency in a small area, but also to have good electrical properties, safety and more stringent use conditions …
In recent years, smart phones and tablet computers have become important product projects that drive the continuous optimization of computer technology. Not only are the products thinner and lighter, but the functions are not diminished, and even the performance of the products can be doubled or even increased several times in terms of performance, storage capacity and battery life. Apart from the integration effect of semiconductor technology in 3D IC and high-order heterogeneous packaging technology, on the other hand, the technical capability of PCB carrier board is upgraded to meet the challenges of new components and smaller volume and narrower internal space.
The circuit board has a great impact on the electronic industry.
In fact, long before the appearance of printed circuit boards, most of the components and circuits of electronic products were constructed by directly connecting electronic parts with copper wires to complete the conduction circuit and construct the whole operational electronic product system. However, the electronic circuit constructed in this way, on the one hand, takes a lot of manpower and effort to make the circuit and connect the components manually, and it is easy to make the wrong connection between the circuit and the components, resulting in the loss of components or materials, which only increases the cost of manufacturing and verifying the circuit.
The improvement scheme is to use electronic circuit board to make circuit through metal chemical etching circuit, and match with drilling holes to provide more stable connection and fixation of electronic components, so as to achieve better wiring quality and component fixation effect. At the same time, higher-quality circuit can be provided in manufacturing, verification, even after product delivery, service sales and maintenance.
Because the printed circuit board (PCB) plays a key role in carrying a large number of electronic components and constructing the conductive circuit of components, PCB has also become an important component for the continuous evolution and upgrading of electronic products! The circuit manufacturing of PCB is mainly divided into two ways. Basically, the PCB itself must have an insulating carrier, and the material of the carrier determines the strength, insulation effect and basic electrical performance of the PCB itself. The conductive circuit can be constructed by two different manufacturing ways: Additive process (additive) or Subtractive (subtractive).
Soft board? Advantages of hard board service conditions are different.
The additive process is made by metal plating, evaporation or conductive material addition of the physical circuit on the substrate; The subtraction rule is to take the printed circuit pattern on the substrate covered with the metal conductor layer, and then remove the unprinted wireless circuit block metal by chemical solvent etching to form a circuit.
In the early days, substrate materials once became the bottleneck restricting the application of circuit boards. With the introduction of all kinds of machine board materials that take into account flexible soft materials, high-temperature resistance, thinning and multi-layer stacking applications, among them, high-priced soft or flexible circuit boards often use additive process processing circuits, while hard circuit boards or multi-layer circuit boards often use subtraction method to make circuits. Because of the different application environments and material characteristics, soft (flexible) circuit boards and hard circuit boards are different. Among them, the amount of hard circuit boards is much larger, and advanced products such as more precise multilayer boards and high-density multilayer boards have also been developed, which has become a key core material technology for the design goal of thin, small or lightweight electronic products.
Test the precision of manufacturing and chemical treatment from single layer to double layer or even multiple layers.
Generally, the conductive layer (circuit) of the substrate can be set on the upper and lower sides of the substrate, and the upper and lower circuit lines can be connected by drilling holes and electroplating through holes in the holes. With the demand of the electronic product industry for high-precision and high-complexity integrated circuits, many hard circuit boards are stacked, matching with the conductive connection and bonding design between circuit layers and layers, so as to construct a multilayer board structure with more complicated circuits.
Multilayer circuit board can effectively simplify the size and area of the substrate, especially with highly integrated components of IC technology. The circuit carrier board can even reduce the spectrum of traditional circuits by several times to dozens of times, which has become the key design trend of actively reducing and optimizing electronic products.
The integrated design of multilayer board and high-density circuit board not only has the technology of WIP far higher than that of conventional circuit board, but also the profit of products is much higher than that of conventional products. However, there are also more problems. For example, because of the material characteristics of multilayer board, the temperature generated by the operation of electronic products will also cause the board to heat up and shrink down. If the connection structure of high-density circuit and the circuit connected between layers is weak, it may also cause the circuit break or abnormal conduction state because of the high operating temperature of products.
Therefore, although the high-density multilayer board has the advantages of high profit and high material volume reduction, the derived testing and verification work will be more complicated and require higher requirements. The precision and temperature change of the material also need to be optimized by the substrate material to provide high stability and temperature resistance, so that the terminal electronic products can better meet the design requirements.
The choice of metal layer material affects the electrical properties of the circuit.
In addition to the material characteristics of the substrate, the metal layer placed on the substrate is also the key to the overall performance of the circuit board.
Generally speaking, the different materials of metal layers have great cost difference, which will also directly affect the production cost, while corresponding to the weldability, corrosion resistance and wear resistance of different metal materials? The plugging and unplugging, electrical resistance, thermal conductivity, etc. are all very different. In practical application, the more expensive the materials, the better. Instead, it is necessary to select appropriate metal material processing circuits according to the use requirements of different metal layers. Common metal layers include copper, tin, lead-tin alloy, tin-copper alloy, etc. The thickness of tin is mostly 5~15μm, and the thickness of lead-tin alloy is mostly 5 ~ 25 μ m.
At present, circuit boards are mainly composed of circuits and patterns. Generally, the circuits and patterns are made together, while the insulation board of the base material itself establishes the insulation properties (Dielectric layers) of each layer. The carrier boards of each layer form application circuit connections through through through holes/vias. Generally speaking, the larger through holes are used for setting electronic components to be soldered by plug-ins, and the other circuit boards will
Last-stage process combined with plate treatment to improve the stability and durability of circuit board.
If the composite board itself is humid in the air, it is easy to change and deform due to moisture absorption, and the deformation process may cause the line wires to break or have poor contact. In order to prolong the service life of the board, a layer of epoxy resin is usually added to the non-welded surface or the board surface, or it is matched with the reference information such as the name, location, version number and date of manufacture of the screen printed components.
As the copper surface and conductive metal surface on the circuit board directly contact with the air, it is very easy to cause problems such as plate oxidation, poor tin coating or copper foil falling off due to oxidation modification. Generally, after the completion of the circuit board, it is still necessary to add an anti-oxidation protective layer on the metal surface that needs to eat tin, for example, by Hot-Air Solder Leveling；; HASL), electroless nickel/immersion gold; ENIG), immersion silver (Immersion Ag；; ImAg), Immersion Tin, or organic solderability preservatives; OSP) protect metal contacts.
As for the verification of the finished circuit board, because the circuit board manufacturing process is complicated, in order to make the products more sophisticated and reduce the number of defective parts, the manufacturing equipment should be regularly maintained and cleaned to maintain stable manufacturing conditions, and the production should be conducted in a highly clean environment to avoid errors in the finished products.
The treatment of the plate is a multi-step chemical liquid immersion and treatment operation, and the equipment must maintain automatic temperature setting, timing and speed processing of the material. At the same time, chemicals should be added at any time according to the PH value of the liquid material during the manufacturing process to maintain the composition stability of the chemical immersion material.
In addition to maintaining the quality of products according to the standard of manufacturing process, the quality of products must also rely on a high cleanliness environment to avoid the contamination of materials. For example, if the production line can be processed in a dust-free environment, the liquid photoresist production line must be processed with PCBA under the conditions of falling dust filtration and surface dust removal.
That is, pay close attention to each stage of production, maintain consistent quality and reduce production defects.
In order to maintain the output quality of the latter part of the workpiece, the quality problems should not be ignored in the processing of each PCBA processing section, and the defects in the process will greatly affect the quality of the final product. The first product inspection, the last product inspection, and the sampling and monitoring of intermediate products are required in each process to maintain the supervision of PCBA processing quality.
In the drilling process section, a Pin-Guage can be used to check the aperture state and verify the quality of the first product. In the electroplating process, a palm-shaped hole copper thickness gauge can be used to check the thickness of the copper plating, and the copper density of the holes and the bonding condition of the inner layers can be checked with slices to ensure the quality of the plated holes. After the copper-plated plate is edged, glass fiber, resin and powder are removed, and then the copper surface is leveled with an abrasive belt machine to remove copper nodules and dents.
At the same time, mass production is assisted by machine vision, supplemented by automatic optical conveyor belt for workpiece inspection, while the interlayer alignment of multilayer boards can be matched by X-Ray inspection to confirm the alignment accuracy. In addition, the automatic optical inspection can be compared and analyzed with the original circuit artwork to prevent the fixed break of the workpiece, circuit short circuit or circuit gap.
In the solder resist process stage, after the bare copper plate is pickled, brushed and slightly etched, it is necessary to remove the oxide layer and micro-copper powder on the copper surface and increase the roughness of the copper foil surface itself, so as to improve the adhesion of the solder resist layer of ink and the ability to protect the circuit board. In the printing stage, the ink uniformity can be visually inspected, and the thickness of the coated ink must be measured with a film thickness meter after the circuit board is baked.
In the lamination stage of multilayer board, the key lies in the control of temperature and pressure. To achieve the best lamination, two-stage treatment and lengthening two-stage hot pressing time can strengthen the hardness and flatness of the board and the adhesion of copper foil. The final circuit board product verification can generally be output by CAM Data, which is matched with the automatic fixture software to construct the fixture making program, and the defective workpiece can be quickly detected and selected through the fixture.
The finished product of multilayer board can be quickly screened out by jig and verification program.
Using the precision contact probe, the circuit conduction quality and condition of the circuit board can be quickly detected.
Multilayer circuit becomes more and more complicated, which not only complicates the manufacturing process, but also increases the difficulty of product verification.
As the size of the circuit board becomes smaller and the complexity increases, it is necessary to carry out various electrical tests with high-level test equipment to avoid problem boards and improve the manufacturing quality of electronic products.
