Solder Mask

The main difference between temporary solder mask and solder resist (overcoat) lies in their purposes and longevity. Temporary solder mask is used for selective soldering and rework processes and is removed after its intended use, while solder resist is a permanent coating applied to the entire PCB surface to provide long-term protection and prevent solder bridges.

Temporary solder mask, also known as peelable solder mask or removable solder mask, is a type of masking material used in the electronics manufacturing process. Its primary purpose is to protect specific areas of a printed circuit board (PCB) during the soldering process, while allowing other areas to be exposed for soldering. After the soldering process is complete, temporary solder mask can be easily removed by peeling or washing it off (depending on the type of mask), leaving the protected areas clean and free of any excess solder. This allows for easy access to the designated areas for subsequent assembly steps or inspections.

For more in depth information, check out "Ultimate Guide to Temporary Solder Mask".

None of our masks contain silicone and they leave no residue behind.

Solder mask is engineered to withstand molten solder temperature for the very brief time (about a second) it is exposed in a typical wave soldering process. Most commercially available masks should be able to withstand melting point temperatures of lead-based and lead-free solder, up to 650°F (343°C). As exposure time is lengthened, like in a reflow oven, there is more potential the mask will bubble, char, and become brittle. How long a mask can withstand extreme temperatures depends on the thickness of the bead, and the type of mask.

Temporary solder mask is intended to be just that – temporary. Manufacturers of solder masks, like Chemtronics, always recommend removing the mask because there is no testing to support doing otherwise. If you decide to leave the solder mask on as a permanent part of the PCB, you will have to do your own functional and reliability testing to ensure it does not cause a problem.

No, temporary solder mask will not leave behind ionic residue that can lead to dendritic grown and board failure.

Peelable mask is usually removed by hand or with tweezers. Resourceful engineers have come up with devices with rotating brushes and other creative methods, but there is no commercially available equipment to speed this process along. Washable mask is engineered to be removed in an aqueous inline or batch wash system. If you are using a closed-loop system, which filters and recirculates wash water, make sure you use a mask that is compatible with your physical filters and ion beds. If you experience foaming, it is an indication that either too much mask material is being passed back into your cleaning system or it is interacting with dissolved flux in the same wash water. This is generally solved by replacing your wash water with fresh DI water, but a defoaming agent can be added as a stopgap solution.

If you think of spot mask as basically liquid masking tape, the application become more intuitive:

1. Apply the mask to the contact areas to protect. Allow mask to fully cure.
2. Apply the conformal coating.
3. After the coating is dry to the touch, but before it is fully cured, peel off the mask. Otherwise it could create a cracked, ragged edge, or even pull up the coating.

Spot mask can be hand applied, dispensed with a pneumatic system, or stencil printed. To hand apply using a squeeze dispensing bottle:

1. Hold the mask bottle upright, but at an angle (around 60°).
2. Squeeze the bottle as you drag is across the areas to be masked
3. For best results, allow mask to fully cure before running through extreme soldering temperature.

The follow are factor to consider when trying to avoid breakage: 1) Curing – Partially cured mask will have more of a tendency to break or leave residue. 2) Temperature and duration in extreme heat – Mask is designed for wave soldering, which is about a second of exposure to molten solder temperatures (generally 550°-650°F). If the mask is sent through a reflow oven the duration is much longer, which can lead to more mask brittleness. If the mask is exposed to high-temperature solder (e.g. silver), it can also lead to more brittleness. 3) Application method – When hand applying, we recommend holding the bottle at about a 60° angle, rather than upright at 90°. That tends to apply the material as a thick blanket over the areas to be masked. When the bottle is held at 90°, the mask is generally applied thinner, and is forced through holes and around components. Those thin areas are more likely to become brittle and stay behind, and mask pushed into holes and around components is harder to remove, so more likely to break.