Introduction To The DFM Problems Affecting PCB Design

Design For Manufacturability(DFM) is from the product development and design, consider the manufacturability and testability, makes the close relationship between design and manufacturing, from design to manufacturing a successful goal. This is the most effective way to ensure the quality of PCB design. In PCB design, what we call DFM mainly includes device selection, PCB physical parameter selection and PCB design details.

Some DFM problems affecting PCB design

1. Package size in line with IPC standard

The pads in contact with the device on the PCB are very important in determining whether the device can be soldered reliably. If the package is designed to meet IPC standards, it ensures that the components are soldered correctly during the manufacturing process.

2. Uniform connection of device pads

For SMD devices of size 0402,0201 or smaller, uniform connection of pads is very important. This prevents tombstone effect, in which the component partially or completely disconnects from the plate during reflow, directly causing the failure of the assembly plate.

3. Vias in SMD Pad

The translation is a little awkward, simply said in the solder pad punched holes. The consensus in PCB design is that Vias in Pad should be avoided as much as possible at all costs.

4. Selection and placement of components

Many designers minimize the use of in-line devices (THTs), or place in-line devices on the same side of the board. However, in-line devices are often unavoidable. In the case of combination, all components should be as close together as possible if the in-line components are placed on the top layer and the patch components on the bottom layer. In some cases, this will affect single-sided wave soldering. In this case, more expensive welding processes, such as selective welding, are used.

5. Uniform distribution of copper foil

Creating a copper foil image on a single sheet depends on a number of factors. If the copper foil is removed in a certain area, it is difficult to guarantee the stability of a single wire. Therefore, it is recommended to distribute the copper foil evenly as far as possible.

6. SolderMask

Many designers like to use an empirical value of 50um to define the size of the pads and also define the minimum spacing between the pads and the wires to be 50um. However, the minimum size should be 75um if you wish to have a solder bridge between the two pads. These factors should be taken into account when creating a component library or placing devices on a PCB, otherwise the spacing is too small to properly cover the area between the pads.