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PCB components are soldered to the PCB through lead holes in the PCB,and the PCB wiring connects the pads together to realise the electrical connection of the components in the circuit.The lead-in holes and the surrounding copper foil are called PAD pads.
PAD pad types
1.Square pads: PCB components on the large and small,and printed wires are simple to use.In the handmade PCB, the use of this pad is easy to achieve.
2.Island-shaped pads:pads and pads between the wires into one.Commonly used in vertical irregular arrangement of the installation.For example,the receipt of the answer recorder is often used in this pad.
3.Tear drop pads:when the soldering pads are connected to the alignment of the smaller often used to prevent pad skinning,alignment and pad breakage.This pad is commonly used in high-frequency circuits.
4.Polygonal pads:used to distinguish between close to the outer diameter and aperture of different pads,easy to process and assemble.
5.Oval-shaped pad:this pad has enough area to enhance the peeling resistance,commonly used in dual-row in-line devices.
6.Open-shaped pads:in order to ensure that after the wave soldering,so that the manual patch soldering pad holes are not sealed by the solder commonly used.
7.Round pads:widely used in the regular arrangement of components in a single, double-sided PCB.If the density of the board allows, the pad can be larger, the welding will not fall off.
Some soldering defects are often found in PCBA hit pieces, and these defects are directly related to the process of PCBA processing, solder, materials, etc.In addition,they may also be related to the design of the pads, such as spacing, size and shape.
PCB pad shape and size
1.The use of standard PCB packaging library in the design process.
2.There are pads on one side of the smallest not less than 0.25mm,PCBA playing pieces of the pad diameter can not exceed the component aperture 3 times.
3.Neighbouring pad edge spacing needs to be kept above 0.4mm.
4.PCB aperture diameter of more than 1.2mm or pad diameter of more than 3.0mm pads should be designed as a diamond-shaped or plum-shaped pads.
5.PCBA playing pieces in the wiring more dense case, it is recommended to use oval and oblong connecting discs.Single-panel pad diameter or minimum width of 1.6mm;double-panel weak circuit pads only need to add 0.5mm to the diameter of the hole can be, the pad is too large easily cause unnecessary welding.
PCB soldering pad hole size standard
The inner hole of the soldering pad for PCBA processing is generally not less than 0.6mm, because it is not easy to process the hole smaller than 0.6mm when the hole is opened and punched, usually the value of the metal pin diameter plus 0.2mm as the inner hole diameter of the soldering pad, such as resistor metal pin diameter of 0.5mm, the inner hole diameter of its soldering pad corresponds to 0.7mm, and the soldering pad diameter is determined by the inner hole diameter.
PCB soldering pad reliability design points
1.Symmetry, in order to ensure the balance of tension on the surface of the molten solder, the two ends of the pad must be symmetrical.
2.Pad spacing, pad spacing is too large or too small will cause welding defects, so to ensure that the component end or pin and pad spacing.
3.The remaining size of the pad, component ends or pins and the remaining size of the pad after the lap must ensure that the solder joints can form a crescent surface.
4.The width of the pad should be basically the same as the width of the component tip or pin.
In the PCBA playing parts,PCB soldering pad design is very important, pad design will directly affect the components of the weldability, stability and heat transfer, related to the quality of the patch,this in the design of PCB soldering pads, you need to design in strict accordance with the relevant requirements and standards.
PCBA playing pieces in the pad design requirements
1.For the PCB components on the welding surface,larger components (such as triode, sockets, etc.) of the pad should be appropriate new.For example,SOT23 pads can be extended by 0.8-1mm to avoid the component ‘shadow effect’ caused by virtual welding.
2.The size of the pad should be determined according to the size of the component.The width of the soldering pad is equal to or slightly larger than the width of the component's welding bar, the best welding results.
3.Generally between two interconnected components,avoid using a single large pad,this is because the solder on the large pad will connect the two components to the middle.Usually the correct approach is to separate the two components of the pads,in the middle of the two pads with a smaller wire connection,if the requirements of the wire through the larger current can be connected in parallel to a number of wires,wires covered with green oil.
4.PCB components on the pad or in the vicinity of the pad can not have through holes,otherwise after the reflow oven,the solder on the pad will melt and flow along the through holes, resulting in virtual soldering,less tin, but also may flow to the other side of the PCB resulting in a short circuit.