PCB Technical - Design of practical PCB board

This paper introduces some principles of PCB design suitable for modern welding technology, and expounds the overall design of PCB, substrate flow direction, manufacture of reference point, component arrangement, pin spacing and other problems needing attention.

1 Introduction

With the gradual increase of domestic circuit board processing and welding manufacturers, the old generation of engineers who have been used to "manual workshop" production and many young engineers who have just entered this field are interested in the new products for mass production; The process requirements of reflow and wave soldering for PCB welding are not well understood, and have restricted their R & D progress and production efficiency to a certain extent. This paper discusses the practical application of modern welding technology; Some principles of PCB design are introduced.

PCB board

2. Overall design of printed board

(1) Process clamping edge of printed board. In surface mount production and wave soldering, a certain edge shall be reserved for the printed board to facilitate equipment clamping. The range of this clamping edge shall be 5mm, and no pad graphics and components are allowed within this range.

(2) The radius of the four corners of the printed board shall be a fillet of 2-2.5mm, so that the printed board can enter the equipment smoothly (see Figure 1).

(3) The overall dimension of the printed board shall be determined according to the equipment specification. The standard dimension of many domestic companies is 50mm * 50mm * 50mm; 330mm * 250mm * 2.5mm. For printed boards smaller than the size, the form of splicing shall be adopted, and the size of splicing shall also meet the above standards. The recommended thickness is 0.9-1.6mm

(4) There are roughly two ways of splicing: Stamp hole and b.v-groove. For stamp hole splicing, it is required that the slot should not be too large. If it is too large, the sensor of the equipment will fail, and the printed board may be damaged during transmission. When the shape of the printed board is irregular, this method is adopted for splicing; For V-groove splicing, the depth of V-groove shall not be too deep. If it is too deep, it will affect the overall strength of the substrate and inconvenience the processing, especially when there are many large components on the substrate. When the shape of the printed board is relatively regular, this method is adopted for splicing.