PCB Technical - PCB chip component package pad design size standard

1. Concept

PCB board is the basic material of PCB, often called substrate. Copper Clad Laminate (Copper Clad Laminate, full name Copper Clad Laminate, CCL in English), is made of wood pulp paper or glass fiber cloth as a reinforcing material, impregnated with resin, covered with copper foil on one or both sides, and then heated and pressed. Into a product. Copper clad laminate is the basic material of the electronics industry, mainly used in the processing and manufacturing of printed circuit boards (PCB), which are widely used in televisions, radios, computers, computers, mobile, communications and other electronic products.

Two, classification

When selecting a sheet, an engineer often pays great attention to a TG value. In this case, we should especially introduce what TG is and the classification of copper clad laminates according to TG.

Glass Transition Temperature Tg (Glass Transition Temperature): It is the temperature at which the polymer changes from the glass state to the high elastic state. The glass transition temperature is an important parameter for the physical change of the polymer, which is mainly related to the structure, aggregation state, and crosslink density of the polymer. 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, for various types of glass fiber cloth-based copper clad laminates, the lowest Tg index value, or Tg index range, is specified. This is actually the use of Tg to classify the heat resistance grade of each type of board. For example: Tg140 degree Celsius, Tg160 degree Celsius, Tg180 degree Celsius and so on. Therefore, for high-reliability PCB designs, designers tend to choose high-Tg plates. Tg is indeed a representative symbol for the heat resistance of plates in leaded soldering.

3. Classification of grades

FR-4A1 level: This level is mainly used in military industry, communications, computers, digital circuits, industrial instrumentation, automotive circuits and other electronic products.

FR-4A2 level: This level is mainly used for ordinary computers, instrumentation, advanced home appliances and general electronic products. This series of copper clad laminates are widely used, and each performance index can meet the needs of general industrial electronic products.

FR-4A3 level: This level of copper clad laminate is a FR-4 product developed and produced specifically for the home appliance industry, computer peripheral products and ordinary electronic products (such as toys, calculators, game consoles, etc.). Its characteristic is that under the premise that the performance meets the requirements, the price is extremely competitive.

FR-4AB grade: This grade of sheet material is a unique low-grade product. However, various performance indicators can still meet the needs of ordinary home appliances, computers and general electronic products, and its price is the most competitive, and the performance-price ratio is also quite excellent.

FR-4B grade: This grade of board is a secondary product, with poor quality stability. It is not suitable for large-area circuit board products. Generally, it is suitable for products with a size of 100mmX200mm. Its price is the cheapest, but customers should choose to use it carefully.

CEM-3 series: This type of product has three substrate colors, namely white, black and natural color. Mainly used in computers, LED industry, clocks and watches, general household appliances and general electronic products (such as VCD, DVD, toys, game consoles, etc.). Its main feature is good punching performance, which is suitable for large quantities of PCB products that require stamping process forming. This series of products has three quality grades: A1, A2, and A3. Customers with different requirements can choose to use them.