Some DFM Issues Affecting PCB Design

Label:Design For Manufacturability, PCB Design, Solder Mask

Dec 30, 2020360

Some DFM Issues Affecting PCB Design

Design For Manufacturability (DFM) is to consider manufacturability and testability from the time of product development and design, so that design and manufacturing are closely linked to achieve the goal of success from design to manufacturing. This is the most effective way to ensure the quality of PCB design.

 

In PCB design, what we call DFM mainly includes: component selection, PCB physical parameter selection and PCB design details.

 

Then, we will introduce some DFM issues that will affect PCB design.

 

1. Package Size that Meets IPC Standards

 

The pad that contacts the device on the PCB is very important, it determines whether the device can be reliably soldered. If the package design meets the IPC standard, it can ensure that the components are soldered accurately during the production process.

 

 

 

2. Uniform Connection of Device Pads

 

For 0402, 0201 or smaller SMD devices, the uniform connection of the pads is very important. This can prevent the tombstone effect: the component is partially or completely separated from the board during reflow soldering, which directly causes the failure of the assembly board.

 

3. Selection and Placement of Components


Many designers try to reduce the use of THT as much as possible, or place the THT on the same side of the board. However, THT are often inevitable. In the case of combination, if the THT is placed on the top layer and the components is placed on the bottom layer, all components should be as close as possible. In some cases, this will affect single-sided wave soldering. At this time, it is necessary to use more expensive welding processes, such as selective welding.


4. Uniform Distribution of Copper Foil

 

Creating copper foil images on individual board layers depends on many factors. If the copper foil is removed in a certain area, it is difficult to ensure the stability of a single wire. Therefore, it is recommended to distribute the copper foil as evenly as possible.


 


5. Solder Mask


Many designers like to use an empirical value of 50um to define the size of the pad, and at the same time define the minimum distance between the pad and the wire as 50um. However, if you want a solder mask bridge between the two pads, the minimum size should be 75um. These factors should be considered when creating the component library or placing the device on the PCB, otherwise the solder mask will not be able to properly cover the area between the pads because the pitch is too small.


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