On a PCB with a patch, in order to locate the entire PCB, it is usually necessary to place the optical positioning points on the four corners of the PCB, generally three. Common reference points mainly include three types of board reference points, unit reference points and local reference points.
1. Reference point structure
(1) Panel datum point and unit datum point.
Shape/Size: 40mil diameter solid circle. FS Technology Solder Mask Window: A circle concentric with the reference point, the size is twice the diameter of the reference point. A 2mm diameter edge requires a round or octagonal copper wire as a guard ring. The internal background of the optical positioning reference symbols on the same board should be the same, that is, whether there is copper foil under the three reference symbols should be consistent.
(2) Local datum point.
Parts such as QFP and pitch ≤0.4mm BGA, CSP, FC need to place local fiducials. Size/Shape: Solid circle, 40mil diameter. Solder mask opening: The size is processed according to the ordinary pad, and the outer ring copper ring cannot.
2. Place the datum point:
General principles:
The veneer for processing SMT equipment must be placed with fiducial points. The number of single-sided reference points is greater than or equal to 3. For single-sided layout, simply place the datum point on the component face. ..When A5I5^0L-z1m+PPCB is double-sided layout, the fiducials are placed on both sides. For the datum points placed on both sides, except for mirror splicing, the positions of the datum points on both sides are basically the same.
(1) The reference point for FS Technology to place the puzzle.
Panel datum points and cell datum points need to be placed. There are three panel fiducials and unit fiducials. The edges of the board are distributed in an L shape, and keep them as far away as possible. Figure A below shows the location requirements for the panel datum points. When using a mirror-symmetrical panel, the reference point on the auxiliary side must meet the requirements of overlapping after flipping, as shown in Figure B below.
(2) The datum point for placing the cell board.
The number of reference points is three, distributed in an L shape on the edge of the board, and the distance between each reference point should be as far as possible. The edge of the reference point must be greater than 5mm. If all four edges are not guaranteed to be satisfied, the transmission edge should at least satisfy the requirements.