Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Info. on Stencil cleaners

Jason Birch


Info. on Stencil cleaners | 29 November, 1999


Can anyone recommend a stencil cleaner manufacturer? Are there any advantages to using ultrasonic vs. high pressure? I am also looking to clean misprinted boards with the machine.


J. B.

reply »


Re: Info. on Stencil cleaners | 29 November, 1999

Hello Jason, I will look for the best price and service support to start. Also request an in house trial at the vendor. Jason, are you looking to remove a no clean paste or water soluble paste?

Single Chamber Equipment: Most stencil cleaners operate with a single chamber utilized for both washing and rinsing operations. Even though segregated wash and rinse tanks are utilized, single chambers have a tendency to create extensive chemical drag-out (wash solution entering the rinse tank). This is most commonly an issue when the process chamber is large and when common plumbing between the wash and rinse is utilized. When a single process chamber is used, the customer should expect increased drag-out due to the surface area of the chamber. This increased drag out makes close-looping the stencil cleaner relatively and economically difficult. Care should be taken in choosing your equipment.

Re-deposition of Solder balls: Another area commonly overlooked, is the equipment�s capability and capacity to remove the solder balls from the process tanks and chamber. This is not as easy as it sounds. Centrifuge and inline filtration�s are common methods utilized. In a dedicated stencil cleaner this is not necessarily an issue. In equipment used to clean Mis-prints, or especially double sided secondary side misprints, this is a major concern. The equipment capability to remove solder paste from the process chambers and spray manifolds is becoming an increased concern. Due to the higher applications of double-sided reflowed assemblies, solder balls must be removed. If solder balls are not removed from the process chambers, the high pressure and high flow created by the pumps will �whip-up� the solder paste and re-deposit the paste on to the circuit board. This can create reliability issue in the field.

Double Sided Reflowed Assemblies: The concern here is the double-edged sword. A lot of manufacturers have spent considerable resources to remove cleaning from the assembly process. It is commonly overlooked with double sided reflowed assemblies of how to clean the primary side of the assembly if the secondary side is misprinted. The concern is viable. Now that the primary side has been reflowed, and the secondary side has been Mis-printed, the primary side must either have no cosmetic effects after cleaning, or the cleaning equipment must have the ability to remove all the reflowed residues from the primary side of the assembly. Thus, we are cleaning again. If a PWA manufacturer has purchased equipment dedicated to ultrasonic energy, and the customer does not approve of components on the primary side being subjected to this energy, you will be hand cleaning these assemblies. If the equipment is of an atomized spray design, considerable pressure and flow may need to be used to remove these reflowed residues. Jason, feel free to contact me off line with further questions or issues Best regards, Charlie

reply »


Re: Info. on Stencil cleaners | 29 November, 1999

There are three primary methods of stencil cleaning.

� Hand Cleaning � Spray-In-Air Cleaning � Ultrasonic Cleaning

Hand Cleaning: Hand cleaning involves the removal of solder paste or adhesives from stencils using a chemically saturated wipe and / or rinsing the stencil in a sink or basin.

Cleaning Performance: Because the cleaning process is completely manual, the degree of satisfactory cleanliness is completely determined by the operator. Manual cleaning provides the lowest degree of cleaning performance and consistency of all cleaning processes.

Stencil Safety: Stencils cleaned by hand tend to suffer the highest rate of damage. Stencils can be damaged when dropped, or when too much pressure is placed onto the stencil by the operator.

Operator Safety: Manual cleaning processes subject the operator to the highest degree of danger compared to all other processes. When removing solder paste from stencils, an operator normally uses a chemically-saturated wipe. The operator, wearing both hand and eye protection would use the wipes to remove the solder paste from the stencil. By nature of the manual process, the operator would be subjected to both lead and chemical exposure.

Environmental Safety: The wipes and gloves, after use, must be treated as hazardous waste due to their lead content and, in many cases, their chemical content. The manual rising process, usually in a sink or basin, will send some solder paste into the sink. Most sinks are not equipped with proper filtration systems to prevent the paste from draining.

The manual process requires hazardous waste disposal of the wipes and filtration of the rinse sink or basin.

Spray-In-Air Cleaning: Spray-in-air cleaning utilizes high-pressure spray nozzles that direct wash and / or rinse fluid onto the stencil surface.

Cleaning Performance: Spray-in-air technology is capable of removing most solder pastes from most stencils. Spray-in-air technology may tend to leave solder paste in the apertures of ultra-fine pitch and even some fine pitch stencils. Solder paste residue may be decreased by increasing the spray pressure or by pre-cleaning the stencil manually prior to placing it into the stencil cleaning system.

Stencil Safety: Spray-in-air technology is generally considered to be stencil-safe when used at moderately low pressures and moderately low temperatures. For fine, or ultra-fine pitch applications however, thorough cleaning normally requires increased spray pressure and temperatures, both of which are capable of causing stencil damage including warpage, and the bending of the land mass between the apertures.

Operator Safety: Spray-in-air technology is considered to be safe when using cleaning chemistries with no flashpoints. IPA and other flammable chemistries, when run in spray-in-air cleaning systems, mandate the use of explosion-proof pumps and fire prevention / suppression equipment. There are many chemistries designed only for immersion cleaning that may not be operated in a spray-in-air cleaning system.

Environmental Safety: Many spray-in-air technologies are capable of operating with environmentally-safe cleaning chemistries. Spray-in-air cleaning systems should be equipped with a filtration system that is capable of removing all solder paste from the cleaning solution. If an environmentally safe cleaning solution is used in combination with a 100% solder paste filtration system, direct discharge may be possible. The cleaning system's filters will be considered hazardous waste.

Ultrasonic Cleaning: Ultrasonic cleaning represents the state of the art in stencil cleaning technology. Ultrasonic cleaning technology utilizes ultrasonic energy to removes solder paste and adhesives from stencils. Ultrasonic energy, emitted from the immersed transducers, is directed to the stencil. Solder paste or adhesives simply "fall off" the stencil without the force or pressure required with all other cleaning technologies.

Cleaning Performance: Ultrasonic technology provides 100% complete removal of all solder pastes and adhesives. Even fine pitch and ultra-fine pitch stencils are cleaned completely and quickly.

Stencil Safety: Ultrasonic cleaning technology is considered completely safe for all stencils. Because ultrasonic cleaning does not utilize pressure, force, or severe mechanical agitation, stencils can not be damaged.

Operator Safety: Ultrasonic cleaning technology is considered to be safe when used with most cleaning chemistries. There are many safe cleaning chemistries which are designed for "immersion" cleaning only. These chemistries can not be used in spray-in-air systems. Ultrasonic cleaners are capable of operating with all safe spray-in-air chemicals and all safe immersion-only chemicals.

Environmental Safety: Most ultrasonic cleaning systems are capable of operating with environmentally-safe cleaning chemistries. Ultrasonic cleaning systems should be equipped with a filtration system that is capable of removing all solder paste from the cleaning solution. If an environmentally safe cleaning solution is used in combination with a 100% solder paste filtration system, direct discharge may be possible. The cleaning system's filters will be considered hazardous waste.

Here are some manufacturers of stencil cleaning systems:

Aqueous Technologies (ultrasonic): (800) 218-8128 (that's us) PMR (ultrasonic): (602) 829-8170 Branson (ultrasonic): (203) 796-0400 EMC (spray-in-air): (215) 340-0650 Speedline / Electrovert (spray-under-immersion): (972) 606-1900

Good Chemistries: Zestron: (703) 589-1198 Kyzen: (800) 845-5524 Petroferm: (904) 261-8286

I hope this helps. Feel free to call me at (800) 218-8128 if you have questions.

Mike Konrad

reply »


Re: Info. on Stencil cleaners | 29 November, 1999

Dear Jason,

We keep several published papers, written by industry experts, on our Web Site: click on the "Recommended Reading" button.

The Smart Sonic Stencil Cleaning Process is the only cleaning process that is Certified by the Environmental Protection Agency (EPA) for Environmental Safety, User Safety and Process efficacy.

We provide a turnkey process, from one source, that is moneyback guaranteed to clean any type of solder paste from any fine-pitch stencil.

I would be pleased to discuss your application at any time.

Best regards, Bill Schreiber Tel: 1(800) 906-440-R E-mail:

Your local representative is SMT Solutions, Tel: (513) 748-0986 Contact: Chris Valentine

reply »

Curtis T.


Re: Info. on Stencil cleaners | 29 November, 1999

Jason, We have been running both the high pressure and the ultrasonic washers for several years and there is no comparison. The ulrtasonic (smartsonic) does a great job on all the normal pastes, and when we changed part of our production to a new epoxy paste that was virtually impossible to clean out by hand or high pressure the US did a decent job. However we were not satified with that so we contacted smartsonic and they were very helpfull in getting a solution to our problem. We ended up using a slightly higher concentration of the 440R solution, then we put a heater in the bath to bring it up to about 100'F (you don't want it much hotter than that or you will damage the mesh on your stencils)and it then did an excellent job at taking off what would other wise be a nightmare. Curtis T

reply »



Re: Info. on Stencil cleaners | 3 December, 1999

Jason, Something which has not been addressed in the responses so far is the system which utilizes high volume (flow rate of chemistry over the product), versus high pressure, which indeed has the potential to damage very fine webs on fine pitch stencils. If the right solvency match is made between the cleaning chemistry and the residues to be removed, a gentle, non-damaging flooding of the product with this properly matched chemistry is the proper approach.

reply »

Cost-effective Conformal Coating Machine

MSD Dry Cabinets