PCB Design | Multi-layer board pad design of half cover half exposed design, equal to the large design | Leadsintec

The previous article has given you a brief description of the cover PAD design, exposed PAD design and other two common designs.

Now, let’s talk about the other two designs – half cover and half exposed design, and other large design.

Half cover and half exposed design.

As the name implies, there is a part of the pad, is covered by solder resist ink, while the other part, is not covered.

For details, please see the following figure.

Design diagram.

This design, in general, will not be used, but if the pad is larger, the solder resist window is larger, the impact is smaller, the use of no harm, but if it is a smaller pad, a smaller solder resist window, the impact is larger, the most common problem, is the pad deformation (see the figure below).

But then, this design is difficult to avoid, it is impossible not to use, PCB foundry can only take partial compensation for differences in the approach to optimize, but, can not ensure a complete solution. Therefore, if you encounter such a situation, the PCB in the actual production of PCBA should be based on the real use of the situation.

Again, such as large design.

Equally large design, that is, the pad size and solder resist window size, designed to be the same size.

But usually, experienced designers, will consider this a wrong design.

 

Why?

— From the design point of view, it is not really a problem, but in the actual production process, equal size design, almost impossible to produce, which causes problems. So, normally, experienced designers, would choose to circumvent such problems.

Why, then, would such a design be nearly impossible to produce?

–This needs to be introduced to the pad-related processes in the PCB production process tolerance issues.

Layout design, the designer because of the limitations of their knowledge, often difficult to design, the design information in the actual production of each tolerance, are taken into account, but the PCB foundry in the actual production process, these tolerances are real, and, will affect the final product.

If the PCB pads are designed to equal the design, then most of the production of pads, will be the following state – solder resist ink will certainly cover one side of the pad, resulting in a reduction in the actual available area of the pad, and then the subsequent PCBA production problems, such as triggering false solder.

Therefore, in summary, if the pads can be designed to cover the PAD or PAD, it is best, if conditions do not allow, it is designed to half cover half exposed, and remind the PCB foundry for local compensation optimization, and it is best not to design for equal size.