How to clean SMT stencil

How do you clean the SMT stencil?

The process of printing solder paste using an SMT stencil is one of the most important processes in the circuit board (PCB) mounting process.
In fact, it is said that 70% of product defects in the mounting process are caused by the solder paste printing process, and cleaning the SMT stencil is the key to improving the quality of the printing process.

If the openings in the SMT stencil are blocked by dirt or other matter, there is a risk of defects such as insufficient solder being printed or excess solder paste being printed.
Furthermore, if the pitch becomes narrower due to the increased density of mounting, there is a risk that manual cleaning using a wiping cloth soaked in IPA will not be able to completely clean and remove the solder paste or solder particles.

On this page, we have verified the cleaning performance of a dirty SMT stencil when cleaned using 1. IPA combined with manual wiping 2. HA-4900 cleaning spray combined with manual wiping 3. HA-4900 cleaning spray combined with a handy ultrasonic cleaner 4. Automatic cleaning machine

We hope that you will re-check the cleaning agents and methods used in your company, and use the content of this page to update your cleaning processes.

We will verify the cleaning method for SMT stencils!

Check the SMT stencil before cleaning.

The white specks in the opening are solder particles. Let's see how well they can be cleaned using IPA, SMT stencil cleaning agents, and ultrasonic cleaning machines.

Following page explains the problems that can be caused by solder particles remaining in the openings.

	Trouble solution Printing process and trouble with metal stencils In the reflow process of electronics packaging, the most common method of supplying solder is to print solder paste using a metal mask. This section introduces the explanation of metal masks, the printing process, possible problems and cleaning.

When cleaning SMT stencils with isopropyl alcohol (IPA)

Wipe the front and back of the mask with a cloth soaked in IPA for about 3 minutes. Then finish by wiping it off with a dry cloth.

After cleaning with IPA

There are a lot of solder particles left in the area circled. This cannot be referred to as a successful cleaning...

When cleaning the SMT stencil with cleaning spray HA-4900

Let's try cleaning using the HA-4900 spray for cleaning SMT stencils. Spray the cleaning spray HA-4900 and then wipe it up with a cloth. Wipe it up and clean it for about 3 minutes in the same way as with IPA, and then finish by wiping it up with a dry cloth.

After cleaning with cleaning spray HA-4900

Compared to manual cleaning using IPA, the amount of solder particles remaining on the SMT stencil has been reduced. However, it is not yet perfect.

For stubborn paste and solder particles remaining in small apertures, we recommend cleaning with cleaning spray HA-4900 for SMT stencil , followed by use of a handy-type ultrasonic cleaner (SAWA CORPORATION SC-500H)!

When cleaning SMT stencils using a handy ultrasonic cleaner

After spraying the cleaner, press the SC-500H cleaning head against the opening of the SMT stencil. (Hold it in place for about 5 seconds per location.) Clean both sides with ultrasonic waves, then finish by wiping with a dry cloth.

After cleaning in an ultrasonic cleaner

The solder particles were almost completely removed.

How a handy ultrasonic cleaner works

Lay the attached bat and soft pad. Place the metal mask on the soft pad and apply the cleaning agent. Ultrasonic waves are emitted only while the button on the side of the cleaning head is pressed (the green light will turn on). The cleaning agent, SMT stencil and solder particles vibrate due to the ultrasonic waves, and the solder particles detach from the SMT stencil. The detached solder particles become entangled in the soft pad and do not re-attach to the SMT stencil.