How to clean SMT stencil

Why Metal Stencil Cleaning Is Important

Solder paste and silver paste (Ag paste) printing with metal stencils is one of the key processes in PCB assembly.
Printing quality depends heavily on keeping the stencil apertures clean and capable of transferring a stable amount of paste.

If stencil apertures become clogged with contamination, too little paste may be printed, while accumulated paste may also be transferred unintentionally and cause printing defects.
As assembly density increases and pitches become finer, manual wiping with an IPA-soaked cloth may no longer remove solder paste, silver paste, and fine particles sufficiently from small apertures.

This page compares cleaning performance using the following methods: 1. IPA + manual wiping 2. HA-4900 cleaning spray + manual wiping 3. HA cleaning spray + handheld ultrasonic cleaner 4. Automatic cleaning system

Use these comparison results as a reference when reviewing the cleaning agent and cleaning method used in your own process.

Comparative Evaluation of Metal Stencil Cleaning Methods

The following tests compare cleaning methods using a metal stencil contaminated with solder paste. Similar differences in cleaning performance may also be observed with silver paste.

IPA	Cleaning Spray	Handheld Ultrasonic Cleaner	Automatic Cleaning System
Summary

Metal Stencil Before Cleaning

The small white particles visible in the apertures are solder particles. Let's compare the cleaning results obtained with IPA, a dedicated metal stencil cleaner, and ultrasonic cleaning.

The following page explains printing problems that can occur when solder particles remain in stencil apertures.

	PCB Assembly Technical Column Solder Paste Printing with Metal Stencils: Process and Common Problems Explains metal stencils, the solder paste printing process, common printing problems, and key cleaning considerations.

Cleaning Performance and Limitations of IPA

Wipe both sides of the stencil for approximately three minutes using a cloth soaked with IPA. Finish by wiping the stencil with a dry cloth.

After Cleaning with IPA

Many solder particles remain in the circled areas. Under these test conditions, IPA wiping alone did not remove the particles sufficiently.

Cleaning Performance of HA-4900 Cleaning Spray

HA-4900 is applied to the metal stencil and then wiped with a cloth. As with the IPA test, the stencil is wiped for approximately three minutes and finished with a dry cloth.

	Product Information HA Series SMT Stencil cleaner Aerosol cleaners for removing solder paste from metal stencils. The lineup includes fast-drying HA-1040 and low-odor HA-4900.

After Cleaning with HA-4900

Before Cleaning

Fewer solder particles remained on the stencil than after manual cleaning with IPA, although some particles were still visible. For stubborn contamination and fine apertures, this page next evaluates HA-4900 in combination with a handheld ultrasonic cleaner, SC-500H manufactured by SAWA Corporation.

Improving Cleaning Performance with a Handheld Ultrasonic Cleaner

After applying the cleaning spray, press the SC-500H cleaning head against the stencil apertures for approximately five seconds per location. Clean both sides ultrasonically and finish by wiping with a dry cloth.

After Handheld Ultrasonic Cleaning

In this test, very few solder particles remained visible after cleaning.

HA-4900 and the handheld cleaner can also be used for localized cleaning of clogged apertures during printing or when cleaning the stencil without removing it from the printing machine, helping reduce the time and work associated with resetting the print position.

How the Handheld Ultrasonic Cleaner Works

Place the supplied tray and soft pad underneath the stencil. Place the metal stencil on the pad and apply the cleaning solution. Ultrasonic energy is generated only while the button on the side of the cleaning head is pressed. The cleaning liquid, stencil, and solder particles vibrate under the ultrasonic action, helping detach solder particles from the stencil. Detached particles are captured by the soft pad, helping prevent them from redepositing on the stencil.

Stable Cleaning Quality and Labor Savings with an Automatic Cleaning System

A handheld ultrasonic cleaner can achieve a high level of cleaning, but manually processing many stencils requires time and labor, and cleaning results can vary between operators. For facilities cleaning larger numbers of stencils or requiring more consistent cleaning quality, an automatic cleaning system can be useful. The SAWA ECOBRID SC-AH100-LV, manufactured by SAWA Corporation and also sold by KAKEN TECH, is designed for: ✓ High-speed processing ✓ Reduced damage to stencils ✓ Lower running costs ✓ Reduced VOC emissions The cleaning mechanism and test results are shown below.

Cleaning Mechanism of the Automatic Metal Stencil Cleaner

An ultrasonic cleaning head and vacuum-drying nozzle are integrated into a single unit. The unit operates from both sides of the stencil, allowing cleaning and drying within the same process. According to the product information used on this page, the cleaning-to-drying cycle can be completed in as little as approximately six minutes, depending on conditions.

After Automatic Cleaning (SC-AH100-LV, Cleaning + Drying Time: 7 Minutes)

No solder particles are visibly remaining in these post-cleaning images.

Selecting the Right Metal Stencil Cleaning Method

IPA wiping may not provide sufficient cleaning.

In this comparison test, IPA wiping left solder particles in the stencil apertures. As apertures and pitches become finer, removing solder paste and fine particles by manual IPA wiping can become more difficult. IPA is also a flammable solvent and should be handled in accordance with the latest SDS and the safety, storage, ventilation, fire-protection, and occupational requirements applicable in the country or region of use.

Use a metal stencil cleaner with high cleaning performance.

Switching from IPA to a dedicated metal stencil cleaner can improve cleaning performance depending on the solder paste or other printing material. For stubborn contamination or particles remaining in fine apertures, combining an appropriate cleaner with a handheld cleaning system can also be effective.

Automatic cleaning can reduce labor and improve process consistency.

For larger numbers of stencils or finer apertures, an automatic cleaning system such as the SAWA CLEAN Series can reduce manual cleaning work while helping standardize cleaning conditions. Potential benefits include reducing cleaning labor and processing time and improving consistency of cleaning quality.

Related Articles & Products for Metal Stencil Cleaning

	Product Information HA Series Cleaners for Metal Stencils and Screen Stencils The HA Series is designed for removing solder paste and various adhesives from metal and screen stencils. Products are available for manual and equipment-based cleaning and can be considered when replacing IPA-based cleaning.
	Technical Solutions What Is IPA? Storage and Handling Considerations An introduction to isopropyl alcohol (IPA), commonly used for cleaning in electronics assembly, including basic storage, handling, and workplace-safety considerations.
	PCB Assembly Technical Column Solder Paste Printing with Metal Stencils: Process and Common Problems Explains how solder paste printing with metal stencils works, common printing problems, and cleaning considerations for maintaining printing quality.