Consideration of the aperture size of PCB proofing pad
When PCB proofing plug-in component pads, the pad size should be appropriate. If the pad is too large, the solder spreading area will be larger, and the solder joints formed will not be full, while the copper foil surface tension of the smaller pad will be too small, so the solder joints formed will be non-wetting solder joints. The fit clearance with the aperture element wire is too large, so it is easy to make virtual welding. When the width of aperture ratio lead is 0.05~0.2mm and the diameter of pad is 2~2.5 times, it is an ideal condition for welding.
Pcb proofing according to the requirements of pads is to achieve the minimum diameter, which is at least 0.5mm larger than the maximum diameter of the flange of the solder terminal hole. Test pads must be provided for all nodes according to ANSI/IPC2221 requirements. Node refers to the electrical connection point between two or more components. A test pad needs a signal name (node signal name), the x-y coordinate axis related to the reference point of the printed circuit board, and the coordinate position of the test pad (indicating which side of the printed circuit board the test pad is located on).
Consideration of the aperture size of PCB proofing pad
The aspect ratio of plated through holes has an important influence on pcb proofing manufacturers’ ability to effectively plate through holes, and it is also important to ensure the reliability of PTH/PTV structure. When the hole size is less than 1/4 of the basic circuit board thickness, the tolerance should be increased by 0.05mm When the diameter of the drilling hole is 0.35mm or less and the aspect ratio is 4:1 or more, pcb proofing manufacturers should cover or block the plated through hole in an appropriate way to prevent the solder from entering. Generally speaking, the ratio of the thickness of printed circuit board to the pitch of plated through holes should be less than 5:1. It is necessary to provide information of fixtures for SMT, as well as the temperature bonding technology of PCB assembly layout, so as to promote the testability in the circuit with the help of “fixture for testing the circuit” or “fixture for nail bed”.
In order to achieve this goal, we need to do the following:
1. Avoid plated through holes-probing on both sides of the printed circuit board. Place the test tip on the non-component/soldering surface of the printed circuit board through the hole. This way can allow the use of reliable and cheaper devices. The number of different hole sizes should be kept to a minimum.
2. The diameter of the test pad specially used for detection should be no less than 0.9mm.
3. Do not rely on the edge of the connector pointer for pad testing. The test probe can easily damage the gold-plated pointer.
4. The space around the test pad should be greater than 0.6mm but less than 5mm. If the height of the component is greater than 6.7mm, the test pad should be located 5mm away from the component.
5. Do not place any components or test pads within 3mm from the edge of the printed circuit board.
6. Test pads should be placed in the center of a 2.5mm hole in a grid. If possible, a standard probe and a more reliable fixing device are allowed.
