Refuse to connect tin! 3 types of tin stealing pads are easy to handle
In PCBA production, it is often easy to tackling tin at the tail end of the device. In order to avoid this defect in production, a pair of pads without electrical properties need to be added to the tail of the device during design, which is the tin-stealing pad. Its function is to guide the solder paste or solder to the correct position during the soldering process, thereby improving the one-time success rate of soldering.
In PCB design, we often need to deal with various packaged components, among which SOP, QFP, DIP, SIP, ZIP and other series packaged components need to be treated with tin-stealing pads. This article mainly introduces three common ways to deal with tin-stealing pads.
01 Increase pin pads
● This method is suitable for components in QFP series packages.
During reflow soldering, the increased pin pads can strengthen the attraction of the component pins, which is conducive to the centering and positioning of the components; at the same time, during wave crest and manual soldering, the increased pin pads can also play the role of tin-stealing. The specific requirements are as follows:
01 The pad width is the same as the component pin.
02 The length of the pad is 1-1.5 times the length of the component pin.
02 Add a tin-stealing pad
● This method is suitable for components in DIP, SIP, ZIP and other series packages.
On the basis of the original package, add a side foot pad to achieve the purpose of not soldering the component pins.
The specific requirements are as follows:
01 When the pad package pin spacing is less than 1.27mm, a tin-stealing pad must be added.
02 The size of the tin-stealing pad should be larger than the original pad size.
03 The tin-stealing pad on the back should be added in the downstream direction of the PCBA direction.
04 The tin-stealing pad should be in the same network as the adjacent end pad or suspended, and should not conflict with the end pad to avoid short circuits between different networks when the tin-stealing pad is connected to the end pad.
05 If the tin-stealing pad is located inside the component frame silk screen or covers the frame silk screen, the frame silk screen should be adjusted so that the tin-stealing pad is located outside the component frame silk screen to avoid welding misalignment.
03 Add tail pads
● This method is suitable for components in DIP, SIP, ZIP and other series packages.
Based on the original package, if there is not enough space to add an additional tin-stealing pad at the end pad position, the end pad can be changed to a cone (teardrop) shape.
The specific requirements are as follows:
01 When the package pin spacing is less than 2.0mm, a tail pad must be added.
02 When the package is parallel to the PCBA direction, only the tail pad is added to the end pin.
03 When the package is perpendicular to the PCBA direction, a tail pad is added for each pin.
In PCB design, the treatment of tin-stealing pads is the key to ensuring welding quality and one-time success rate; by increasing the pin pad, adding tin-stealing pads and adding tail pads, the component pins can be avoided from being connected and the welding effect can be improved.
During the processing, it is necessary to select the appropriate processing method according to the packaging and welding requirements of the specific components, and attention should be paid to details to ensure the best welding effect.
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