Cleaning or stripping is the removal of undesirable substances, thin films or residues from a surface. The ability to perform delicate cleaning without damage to the underlying part is a critical benefit of MicroBlasting.
Where Used
AEROSPACE
- Thermocouples – removing MgO to expose contacts for bonding on heat-sensing harnesses
- Circuit boards – conformal coating removal for replacement of failed components
- Ceramic components – removing metalization
- Turbine blades – cleaning casting material, laser remelt and coatings from air holes
- Wire stripping
- Gyro blocks – removing polishing compound
DENTAL LAB
- Crowns – removing oxides from a surface
- Pressable ceramics – divesting (Empress Process)
FOSSILS
- Fossil preparation – removing the matrix surrounding an embedded fossil
ART RESTORATION
- Paintings – removing residues
- Cleaning stone masonry
MEDICAL
- Guidewires – removing PTFE coatings
- Conformal coating removal
- Ceramic components
- Pacing leads
- Stents – removing oxides and HAZ from laser-cut Nitinol stents
- Heart valves – removing graphite core on mechanical valves
- Pacemakers – removing excess encapsulation material
- Catheters
- Defibrillator leads – selectively removing silicone insulation to expose an electrical conductor
INDUSTRIAL CONTROLS
- Conformal coating removal
- Molds – removing EDM recast and discoloration
- Hot runner nozzles – cleaning residue buildup to increase lifespan of expensive nozzles
- Ceramic components
POWER GENERATION
- Turbine blades
- Solar panels – edge deletion
- Solar panels – selective exposure of the molybdenum layer
ELECTRONICS
- Probe cards – removing excess epoxy
- Trimming resistors
- Wire stripping
- Conformal coating removal
- Ceramic components
How To Selectively Clean with MicroBlasting
The selective cleaning process uses the abrasive qualities of MicroBlasting to carefully erode layers of unwanted material from a base substrate. The process takes advantage of the different physical properties of the two layers. Brittle materials can be removed from soft ductile layers, or soft ductile layers can be removed from brittle layers. The difference between selective cleaning and controlled erosion is that controlled erosion is performed on a single material type or layers of material with the same properties.
Removing a Ductile Layer from a Brittle Substrate
Two blasting variables to consider before removing a soft ductile material from a brittle base substrate.
Abrasive Selection
This application usually involves a soft polymer or coating layered over a ceramic wafer, metal structure, or circuit board. The goal is to make sure that the abrasive selectively attacks the top ductile layer without causing damage to the brittle layer underneath. To do so, the abrasive media should be hard enough to cut through the ductile layer but not as hard as the brittle material underneath. Common abrasives used in these applications are sodium bicarbonate, wheat starch, walnut shell, and plastic media.
Particle Velocity
The typical range of pressure for selective cleaning of ductile layers from a brittle substrate is 40-80 psi. High particle velocities can cause the abrasive stream to impact and damage the substrate if the abrasive and the substrate are close in hardness or if the abrasive media contains foreign contaminants.
Removing Brittle* from Ductile
Considerations before removing a brittle material from a soft ductile substrate:
Abrasive Selection
A dense abrasive, like aluminum oxide or glass bead, transfers energy into the brittle layer and fractures it. When it strikes the ductile layer, a broad area absorbs and then releases the energy of the striking abrasive. The elastic nature of the ductile substrate usually protects against erosion.
Particle Velocity
The soft ductile substrate could be burned if too much energy is transferred to the target, so particle velocities should start low and increase gradually,
*MicroBlasting works well when the brittle layer has strong cohesive forces and weak adhesion properties.
Manual and Automated Systems
MicroBlasting provides the flexibility most selective cleaning applications need. A manual system is ideal for lower volume applications. High variation in part geometry or blast location benefits from the skilled eye of an operator using a manual system to selectively target surfaces on parts. For instance, excess epoxy can unevenly distribute on probe rings, and fossils come in all shapes and sizes—from trilobites to T-Rexes.
Some applications may be good candidates for automation but lack volume in their early stages. For example, during the prototyping phase of a new pacemaker, the design is optimized in low volume. Once this technology moves into production, MicroBlasting can transition seamlessly from a manual system to an automated system, primarily because the core blaster stays the same. Automation just provides parts handling and control over the process. This means that the whole selective cleaning process does not need to be re-qualified, it simply needs to be expanded.
The Manual System
Learn more about the AccuFlo®, our most powerful and precise MicroBlaster to date, and the ProCenter Plus™, a chair-height workstation with integrated dust collection. Continue reading →
Automated Systems
MicroBlasting technology integrated with a proven advanced machining platform. Comco has two automated systems: the Advanced Lathe & the JetCenter. Learn more →
PTFE Removal from Guidewires
Guidewires are typically coated with PTFE to improve lubricity. It is far more effective to coat guidewires in long reels than in individual lengths. After the wire is coated and cut to length, sections of the coating need to be removed. The critical aspects of this selective removal application are:
- the delineation from coated to uncoated must be sharp.
- the coating must be completely removed.
- the integrity of the wire must be maintained.
Sodium bicarbonate is an ideal abrasive media for this application because of its physical properties and water solubility. The particles are sharp enough to cut through the PTFE’s long fibrous strands but soft enough to leave the guidewire unharmed. Sodium bicarbonate is listed as a 3 or 3.5 on Mohs. It is ideal for interventional use because it leaves no residue following a standard cleaning process.
Matrix Removal on Fossils
Removing the calcium and rock layers that surround a fossil is challenging and tedious. This matrix can be closely bonded to the fossil itself. While a pneumatic hammer may be used to make the initial “rough” cut, a skilled operator must remove the remaining matrix. The highest potential for damage to a fossil happens during the removal of the final layer. MicroBlasting’s accuracy and control combined with the right abrasive reduces risk to priceless artifacts during this critical operation.
Common abrasives for matrix removal are sodium bicarbonate and pumice. Both abrasives chip away at a brittle matrix without damaging the delicate fossil underneath. The process should be done in a customized WorkStation equipped with a magnifier to enhance control and precision.
Conformal Coating Removal on PCBs
Traditional processes for conformal coating removal from printed circuit boards involve either scraping, using chemicals or using extreme heat—all of which have significant drawbacks. MicroBlasting provides a precise, safe and cost-effective method for removing conformal coating, whether the application requires very inconsistent and selective removal for component testing or replacing, or the application involves high-value boards. Blasting parameters can be configured to differentiate between the coating and the board and set to provide consistent results board-to-board. A wide selection of abrasives is available to suit most types of coating.
MicroBlasting for Static-Sensitive Applications
Our Application Profile page for conformal coating removal provides a comprehensive look at this case study, including a quick guide to abrasive selection. Continue reading →
- Protecting Board Integrity in Harsh Environments – article in Surface Mount Technology
- Micro-Abrasion for Reconditioning Turbine Parts – article in Gas & Diesel Turbine Worldwide
- MicroBlasting for Texturing and Cleaning Molds – article in Plastics Machinery & Auxiliaries
- Turning CIGS Thin Film into Actual Solar Collectors: A Critical Step – article in Global Solar Technology