PCB SMT component package pad design size standard
1. Concept
PCB material is the basic material of PCB, often called base material. Copper Clad Laminate (CCL) is a product made of wood pulp paper or fiberglass cloth, impregnated with resin, covered with copper foil on one or both sides, and hot pressed. Copper clad laminate is the basic material of electronic industry. It is mainly used for processing and manufacturing printed circuit boards (PCB). It is widely used in television, radio, computer, mobile, communication and other electronic products.
2. Classification
Engineers often pay close attention to a TG value when choosing sheets. In particular, what is TG and the classification of copper clad laminates according to TG are introduced.
Glass Transition Temperature (Tg): The temperature at which polymers change from glass state to high elastic state. Glass transition temperature is an important parameter for the physical change of polymers, which is mainly related to the structure, aggregation state and crosslinking density of polymers. For designers, Tg is an important item to measure and characterize the heat resistance of some glass fiber cloth based copper clad laminates (such as FR-4).
In the IPC-4101 standard, the lowest Tg index value or the range of Tg index are stipulated for all kinds of copper clad laminates based on glass fiber cloth. In fact, Tg is used to classify the heat resistance of various types of laminates. For example: Tg140 (?), Tg160 (?), Tg180 (?), etc. Therefore, for high reliability design, designers tend to choose high Tg plate. Tg, as a symbol of heat resistance of plates in lead welding, is indeed representative.
3. Classification
FR-4 A1: This level is mainly used in military, communications, computers, digital circuits, industrial instruments, automotive circuits and other electronic products.
FR-4 A2: This level is mainly used for ordinary computers, instruments, advanced household appliances and general electronic products. This series of copper clad laminates are widely used, and all performance indicators can meet the needs of general industrial electronic products.
FR-4 A3: This class of copper clad laminate is specially designed for home appliances industry, computer peripheral products and general electronic products (such as toys, calculators, game consoles, etc.) development and production of FR-4 products. Its characteristic is that the price has a competitive advantage on the premise that the performance meets the requirements.
FR-4 AB grade: This grade plate is a unique low-grade product. However, the performance indicators can still meet the needs of ordinary household appliances, computers and general electronic products. The price is the most competitive, and the performance-price ratio is quite excellent.
FR-4 B grade: The board of this grade belongs to the second grade, and its quality stability is poor. It is not suitable for PCB products with large area. It is generally suitable for PCB products with size of 100mm X200mm. Its price is the lowest, but customers should pay attention to the choice of use.
CEM-3 series: This kind of product has three kinds of base material color, namely white, black and natural color. Mainly used in computer, LED industry, clocks and watches, general household appliances and general electronic products (such as VCD, DVD, toys, game consoles, etc.). Its main feature is that the punching performance is good, suitable for large quantities of PCB products which need stamping process forming. This series of products have three quality grades of A1, A2 and A3. Customers with different requirements can choose to use them.
