How to Order Boards with Solder Mask Defined Pads
Solder Mask Defined Pads
In most PCB designs, the solder mask clearance is larger than the copper pad it’s exposing, these pads are called Non-Solder Mask Defined (NSMD) pads (also called copper defined pads). The image on the left illustrated an NSMD pad.
Some components (especially some BGA chips) require another type of soldermask/pad structure, called Solder Mask Defined (SMD) pads, it has a solder mask clearance that is smaller than the copper pad and the mask is intentionally printed over a portion of the copper pad. The image on the right illustrated this structure.
You can use the suggested pad and soldermask clearance dimensions in the datasheet and application notes. But please make sure at least 3 mil (0.076mm) of mask will be printed on all sides of the copper pad, as illustrated below. The reason is there’s a registration tolerance on the solder mask placement, if the mask is only slightly smaller than the pad, there’s a chance the mask could shift enough exposing bare substrate which would result in a bad result.
|Abbr. SMD is sometimes confusing because it’s also the abbr. of Surface-Mount Device.|
How to Transfer SMD information to JLCPCB
There isn’t any option to tell JLCPCB a design has SMD pads in the ordering system, so if CAM engineers can’t get this information, the soldermask clearance for SMD pads will be enlarged to become the traditional Non-Soldermask Defined style which will ruin the final boards.
To transfer the SMD information to JLCPCB, you can use the following methods:
1. Write a special instruction
In the ordering system, there’s a text input box call "PCB Remark".
You can write a special instruction to inform JLCPCB your design has SMD pads, like:
Please note: Parts U1, U2... use Solder Mask Defined Pads. Do not compensate/modify the soldermask for them. If you don't known what a Solder Mask Defined Pad is, just ask.
2. Confirm Production File
Select "Yes" for "Confirm Production File" option.
This option works in this way: Engineers at JLCPCB will create the production file required to manufacture the PCB, if the option is checked, you can check and confirm it before production. A confirmation email will be sent to you when the production file is completed.
Download the processed Gerbers, pay attention to inspect the soldermask clearance for the SMD pads.