The construction of the conductive layer (circuit) of the general substrate can be provided on the upper and lower sides of the substrate. Through the drilling and plating of through-holes in the holes, the connecting and connecting circuits of the upper and lower circuit lines are formed. The need for high-precision, high-complexity integrated circuits has also resulted in the stacking of multiple hard circuit boards, matching circuit layers and the connection and bonding design between layers, and constructing more complex multilayer board structures.
Multi-layer circuit boards can effectively simplify the size and area of the substrate. Especially with the 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 a key design trend for active reduction and optimization of electronic products.
The integrated design of multi-layer boards and high-density circuit boards not only has much higher work-in-progress technology than conventional circuit boards, but also has more profits than conventional products, but the problems that follow are relatively more. For example, multi-layer boards The material characteristics of the plate itself, the temperature generated during the operation of the electronic product will also cause the plate to thermally expand and contract. If the connection structure of the high-density circuit and the layer-to-layer conduction connection is weak, the circuit may be disconnected due to the high product operating temperature. Or abnormal conduction status.
Therefore, although high-density multi-layer boards have the advantages of high profit and high material accumulation reduction, the derivative testing and verification work will be more complicated and demanding. The precision and the temperature change of the material also need to pass through the substrate material. Only by optimizing and providing high stability and resistance to temperature changes can the terminal electronic products better meet the design requirements.
Metal layer material selection affects circuit electrical properties
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.
In general, the metal layer materials are different and the cost gap is huge, which will directly affect the production cost, and the corresponding metal materials are weldable, corrosion-resistant and wear-resistant? There are great differences in plug-in, electrical resistance, and thermal conductivity. The actual application is not that the more expensive the material is, the better, but that it is necessary to select a suitable metal material for the circuit according to the needs of different metal layers. Common metal layers are copper, tin, lead-tin alloys, tin-copper alloys, etc. The thickness of tin is mostly 5 to 15 μm, and the thickness of most lead-tin alloys is 5 to 25 μm.
At present, circuit boards are mainly composed of circuits and patterns. Generally, circuits and patterns are made together, and the insulating sheet of the base material itself establishes the insulation electrical properties (dielectric layers) of each layer. Each layer of the carrier board is connected to the application circuit through a through hole (via through hole). Generally speaking, the larger through holes are used for electronic components that require plug-in soldering. In addition, the circuit board is also set to be non-conductive Holes for surface mounting of electronic components.
The final process is matched with sheet processing to improve the stability and durability of the circuit board
The composite board itself is susceptible to mutating and deforming the board due to moisture absorption due to humid air, and the deformation process may cause the line wires to break or have poor contact. In order to increase the life of the board, a layer of epoxy resin is usually added to the unwelded surface of the board or the surface of the board, or with reference information such as the name, location, version number, and date of manufacture of the printed circuit board.
Because the copper surface and the conductive metal surface of the circuit board are in direct contact with the air, it is very easy to cause problems such as oxidation of the board, poor tin loading, or copper foil peeling due to oxidation deformation. Generally, after the circuit board is completed, it is still on the unloaded board. Need to add a layer of anti-oxidation protective layer on the metal surface that needs to eat tin, for example, hot-air Solder Leveling (HASL), Electroless Nickel / Immersion Gold (ENIG), silver dip ( Immersion Ag (ImAg), Immersion Tin, or Organic Solderability Preservatives (OSP) to protect metal contacts.
As for the verification of the finished circuit board, because the circuit board manufacturing process is cumbersome, in order to make the product more sophisticated and reduce the number of defective parts, the process equipment should be regularly maintained and cleaned to maintain stable production conditions, and the production must also be in a high-clean environment Proceed to avoid errors in the finished product.
The processing of the board is a multi-channel chemical liquid soaking and processing operation. The equipment must maintain automatic constant temperature, timing and constant speed processing of materials. At the same time, the process needs to add chemicals at any time depending on the pH of the liquid material to maintain the stability of the chemical impregnation composition.
In addition to the process standard to maintain product quality, product quality must also rely on a high cleanliness environment to avoid material contamination. For example, the production line can be processed and operated in a dust-free environment. The liquid photoresistance production line must be equipped with falling dust filtration and board dust removal conditions. Perform PCBA processing.
Production means paying close attention to all stages of processing to maintain consistent quality and reduce production defectsIn order to maintain the output quality of the subsequent workpieces, the quality issues must not be ignored in the processing of each PCBA processing section. Defects in the process and the quality of the final product will be greatly affected. Each process needs to implement the first product inspection, last product inspection, and intermediate product sampling monitoring to maintain product PCBA processing quality supervision.
In the drilling process section, a pin-guage can be used to detect the aperture state to verify the quality of the first product. The electroplating process can use a palm hole copper thickness gauge to check the thickness of the copper plating, and check the copper density of the pores with a slice. The bonding condition with the inner layer ensures the quality of plated holes. After the copper-plated board is edging, glass fiber, resin and powder are removed, the copper surface is then leveled with a belt machine to remove copper nodules and depressions.
At the same time, high-volume production is equipped with machine vision assistance, supplemented by automatic optical conveyor belts for workpiece inspection, and X-Ray inspection and matching of multi-layer boards for Huai can be used to confirm the precision of alignment. In addition, the automatic optical inspection can be used for comparison analysis with the original circuit artwork to prevent problems such as fixed disconnection, short circuit or line gap of the workpiece.After pickling, brushing, and micro-etching of the bare copper plate at the solder protection process stage, it is necessary to remove the oxide layer and micro copper powder on the copper surface and increase the roughness of the copper foil itself to improve the adhesion of the ink solder protection layer. , While improving the ability to protect the circuit board. In the printing stage, the uniformity of the ink can be inspected visually. After the circuit board is baked, the thickness of the coated ink must be measured with a film thickness meter.
In the multi-layer board pressing stage, the key lies in the control of temperature and pressure. To achieve the best pressing, you can strengthen the hardness, flatness and copper of the board through two-stage processing and lengthen the two-stage hot pressing time. The adhesion of the foil. The final circuit board finished product verification can generally be output by CAM Data and used with automatic fixture software to construct a production fixture production program, and quickly detect and select defective workpieces through the fixture.
Finished multilayer boards can be quickly screened for defective products through fixtures and verification programs.Using precision contact probes, you can quickly detect the quality and condition of circuit continuity. Multilayer board circuits are getting more and more complicated, in addition to the complicated manufacturing process, it also increases the difficulty of finished product verification.
The size of the circuit substrate becomes smaller and the complexity becomes higher. Various electrical tests must be performed with high-level test equipment to avoid problem substrates and improve the quality of electronic products.
Increased difficulty in designing high-density multilayer boards