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Engineering Question 6: Solder Mask Bridges
Posted on 27/05/2016

EQ’s for a variety of printed circuit board design files are common to PCB Global’s Computer Aided manufacturing (CAM) Engineering department. We will invariably have a few Engineering Questions to confirm with our customers, such as the example shown below regarding Solder Mask Bridges.

Solder Mask Bridges

EQ from CAM:

These SMT pads do not have enough space between them to apply a correct solder mask dam. This area will be completely free of solder mask, or can be shaved by 2mil from each SMT pad then apply the solder mask between each section.

Explanation:

Currently this SMT area has the solder mask open as one block. This is an acceptable clearance; however, it can cause shorts between these pads after SMT reflow. By shaving 2mil from each SMT pad, we can ensure there is sufficient distance to allow for exposure of the solder mask file, to apply solder mask between each SMT pad. This ensures the solder mask dam will improve the solder reliability yield after SMT reflow.

The actual distance between SMT pads differs depending on the finished copper thickness/ Below is an example of 1/2/3 & 4oz copper finish:

Solder mask bridge for 1oz copper (4mil)

Solder mask bridge for 2oz copper (5mil)

Solder mask bridge for 3oz copper (6mil)

Solder mask bridge for 4oz copper (6mil)

 Resolution:

With authorisation from our customer, the SMT pads in question had the copper area shaved 2mil allowing a solder mask dam between these IC’s.

For further tips and information when designing and laying out your printed circuit board design file please do not hesitate to contact our PCB Global team at sales@pcbglobal.com