Significance of PCB Cleaning after Surface Mount Soldering

2019-11-26 17:06Writer: qyadminReading:

pcb cleaning solution

 
When cleaning PCB assemblies, the primary goal is to. remove contaminants from populated boards. and hybrid circuits resulting from fluxes and improper handling.  The use of engineered PCB cleaning solutions is essential to ensure flux residues. removed from the assemblies used in high-reliability applications. and industries such as automotive, medical, aerospace, and military. 
 
The targeted use of a cleaning agent improves the integrity of next processes. such as bonding and conformal coating.  Residues can cause improper adhesion of bonds that can lead to failures. such as heel cracks or lift-offs. During the coating process, remaining residues can result in poor wetting. and delamination that can cause assembly failures and lead to field failures.
 
These reliability risks increased when using lead-free solder. pastes as they contain more resins. as well as aggressive activator systems and soldered at higher temperatures.

The following aspects are able to explain the significance of PCB cleaning. after surface mount soldering:

• PCB cleaning after surface mount soldering can stop electrical defects from occurring.
  Among all the electrical defects, electrical leakage is the most protruding one. which is an essential element reducing long-term reliability of PCB boards. This type of defects caused by ionic contaminants, organic residues. and other adhesion substances left on the surface of circuit boards.
  • PCB cleaning after surface mount soldering can drop erosive substances. Erosion will damage circuits, leading components or devices to brittleness. Erosive substances can conduct electricity in humid environment. which will further arouse PCB boards to shorts or even failures. Erosive substances elimination is actually excluding negative elements hindering. long-term reliability of PCB boards.
  • PCB cleaning after surface mount soldering can make board appearance look clear.
  PCB boards cleaned after surface mount soldering. look clear in appearance, making some defects exposed. convenient for inspection and troubleshooting such as heat damage and lamination.

Source Analysis of Contaminants


 White contaminants left on the surface of PCB board. after surface mount soldering feature complicated ingredients. They could be flux, oxide or reagent of flux and metal, solder mask and PCB lamination material. Apart from substances mentioned above, white contaminant generation. correlated with other elements including PCB design. SMT technique (such as reflow soldering time and temperature), temperature and humidity. 

Dry Contaminants (Dust, Dirt)
 

      One of the most common occurrences is the accumulation of dirt or dust in or around the PCB. using a small, delicate brush, such as a horsehair paint brush. can remove dirt and dust without affecting the components. There are limitations on where even the smallest brush can reach, such as beneath a component.
 
      Compressed air can reach many areas but may damage vital connections. so it should used with extreme care.
 
      designed vacuum cleaners for electronic components. are also an option but cannot reach everywhere.
 

Wet Contaminants (Grime, Waxy Oil, Flux, Soda)
 

       High temperature operations can cause some components. that coated in wax to become magnets for dust and dirt. causing tacky grime that cannot removed with a brush or vacuum. Or a product gets a bath of sticky soda, making the board a gooey mess. Either way, these substances should tackled before it builds up and affects performance.
 
      Most grime can removed with a cleaning agent, such as isopropyl alcohol (IPA) and a Q-tip. small brush or clean cotton cloth. Cleaning a PCB with a solvent like IPA should only done in a well vented environment, under a fume hood.
 
      Demineralized water can used as an alternative. Be sure to remove any excess moisture and dry the board. (a few hours in a low-temperature oven can remove any residual moisture.)
 
       There are many available PCB cleaning agents aside from IPA. ranging from acetone to chemicals made for cleaning electronics. Different cleaning agents can address specific types of contaminants. such as solder flux or wax. Keep in mind that harsh cleaning agents can remove component markings. or cause damage to plastics or electrolytic capacitor jackets. or other exotic components like humidity sensors. so make sure you aren’t using a cleaning agent that is too strong. If you can, test the cleaner on an old component or connector you don’t need to be sure you don’t do more harm than good.
 

Ultrasonic PCB Cleaning
 

      Ultrasonic cleaning machines use high-frequencies to cause cavitation. the violent implosion of billions of minute bubbles in the cleaning solution. contained in an ultrasonic cleaner tank. The bubbles. created by transducers bonded to the bottom of the tank . and excited to ultrasonic frequencies by generators. The implosion of these bubbles blasts away. contaminants on the surface of parts cleaned.
 
     Ultrasonic can defined as sound waves that have frequencies. above the upper limit of the normal range of human hearing. which is about 20 kilohertz (20 kHz or 20,000 cycles per second). While that is true, ultrasonic cleaners when operating can heard. due to the action created by what we call ultrasonic cavitation.
 

Benchtop Ultrasonic PCB Cleaner
 

      This technique has lost some favor as a method for cleaning as it can cause damage to components. or loosen connections, along with the dirt and grime. In fact, NASA has issued a directive that it no longer employs ultrasonic cleaning (page 31, section 7.1.4). as it can cause separation of component end caps and actually cause damage to bond wires. and bond wire pads internal to the IC via ultrasonic conduction of the ultrasonic energy. via the integrated circuit lead-frame.
 
     That said, there is still a place for ultrasonic cleaning applications. The ultrasonic cleaning process can reach the most difficult. hard to reach places underneath high density components on most any parts of a circuit board. This is not the case for SMD devices that have small gaps. that are smaller than the surface tension coefficient of the cleaning fluid. But, the process is fast and there are many high-capacity machines. available to address high-volume cleaning needs.
 

PCB Ultrasonic Cleaners
 

        Cavitation is not a gentle process. It has calculated that temperatures more than 10,000°F and pressures. more than 10,000 PSI generated at the implosion sites of cavitation bubbles.
 
Measured in cycles per second, ultrasonic cleaners can produce from 25 kHz to 100+ kHz. Lower frequencies create larger cavitation bubbles compared to higher frequencies. Larger bubbles implode more and used. for example, to remove gross contaminants from fabricated metal components. Higher frequencies create smaller bubbles that clean more. but are better able to penetrate cracks, crevices and blind holes. The higher frequencies used for cleaning polished or delicate surfaces.

How to clean PCB?

 
      Is it recommended not to clean Circuit Boards (PCB) with a cleaning brush. as this can damage the components. the best solution is to use an ultrasonic cleaner following this process. A wash cycle time of 60 minutes required to clean the PCB, dunking after 30 minutes recommended. to help move debris sitting on the part. Rinsing is an important stage about insure the cleaning agent dose not etch or damage the PCB. Recommended rinse cycle of 5 minutes. A drying cycle time of 10 minutes at 65°C
 
      Some of you may feel you can get away with. not cleaning your prototyping PCBs—depending on the locale and design. If that’s the case, good for you! But, despite your fortune thus far, I encourage you to clean your boards. Certain circuits, especially those with sensitive analog circuitry. or RF circuits susceptible to minor impedance changes. should cleaned immediately to make sure performance is not affected. While even the most corrosive flux may not cause any problems in the short term in some environments. over months and years that flux may eat away at that beautiful board you’ve designed. Small traces can open, solder joints can weakened. robustness of the board will go down.
 
      The go-to cleaning kit for any hobbyist. or DIYer is isopropyl alcohol and their old toothbrush. If you’re making a small project for yourself, or making a handful of boards, this is not a bad solution. It removes most of the flux, as well as any other gunk that may be on the board. and should do so without affecting the board’s components. Taking it up a notch, you can use remover designed to remove flux from your boards. Flux remover comes in a variety of strengths. If you’re using a No-Clean Flux (which, , you should clean anyway), then the flux remover doesn’t need to be that strong. If you’re using the same flux for your plumbing and your circuit boards, you want something more robust. While these flux removers made for this purpose. in reality they’re a blend of chemicals that people use when cleaning their boards. On their website, MG Chemicals lists ethyl alcohol, isopropanol, and ethyl acetate. as the components of their particular flux remover. Nothing surprising. but they’ve put together a good chemical balance for cleaning the flux. without the risk of eating plastics like the soldermask and IC packages.
 
      While effective, and inexpensive, cleaning boards with isopropyl alcohol. and a toothbrush does have its drawbacks. Delicate parts can destroyed by the stiff bristles. snapping off leads and sending surface mount devices to oblivion. Also, those small parts have small nooks, crannies, and crevices the toothbrush can’t get to. While the alcohol rinse will help, it won’t remove all the flux without some mechanical action. If you use wipes or some non-linting tissue to wipe the boards instead of a brush. it’s even more of an issue to get into those tight spots. For production-quality cleaning, you may want to look into an ultrasonic PCB cleaner. While the price will be hundreds of times more than that toothbrush. the cost savings in avoiding returned products as well as hits to your reputation will make it clear. that it’s a wise investment.
 
      A clean board is a long-lasting board. If you want to increase the chance of being able to use your board for years, if not decades, after you make it, clean it. Even if you can only afford a toothbrush and some isopropyl alcohol swabs, that’s better than nothing.

best pcb cleaning Tips

 

Using Compressed Air to Clean PCBs

 
   For simple repairs, compressed air provides an unobtrusive way to free up. any dust resting on the electronics. or inside the machines and blow it out. Use short bursts to spray the air inside the ventilation ports. If you’re not satisfied with the dust removed, open the device with a screwdriver. and work your way around the components. cleaning the circuitry with the air.
 
Compressed Air Cleaning Circuit Board
 

Using Baking Soda to Clean PCBs
 

  Baking soda, or sodium bicarbonate. is an effective means of removing grime with minimal risk of damaging the board. It possesses mild abrasive qualities that excel in removing corrosion or residue. that will otherwise not come off with simpler means such as a brush and distilled water. Baking soda is most effective when treating corrosion. as it dissolves the troubled area. and neutralizes the acidic qualities of the residue.
 

Using Isopropyl Alcohol to Clean PCBs

 
Isopropyl alcohol is a great PCB cleaner because it is inexpensive and evaporates . Compared to other cleaners used for similar purposes, alcohol contains fewer chemicals. It is important that isopropyl alcohol used to clean your circuit board is 90% or better. High-percentage isopropyl alcohol can cause adverse effects in contact with the body. so be sure to handle it with care and use latex gloves and goggles.
 

Using Distilled Water to Clean PCBs

 
Distilled water triumphs over any other form of liquid. when mixing your cleaning solution. due to the absence of ions conductive to electric devices. Pure distilled water will not degrade electronic devices, as it is a very poor conductor.
 
It also can become contaminated by dirt found on your hands or in the air, so seal your reserve of distilled water. when not in use and to avoid contact with your bare hands.
 

Using Household Cleaners to Clean PCBs

 
     A phosphate-free household cleaner should also be in your arsenal. While phosphates can be an effective chemical to protect against corrosion. and have other helpful cleaning properties. phosphorous pollution in lakes has become a real concern. for the United States since the 1970s. and many manufacturers have moved away from including them in cleaning products. Since then, companies have adapted to create phosphate-free cleaners. that do the job fine.
 

choice of brush for cleaning PCB

 
     Your choice of brush is also important in the cleaning process. Selecting a brush that has soft bristles and is small enough to reach small places is the best pick. A toothbrush or paintbrush are the best choices. if your company does not have some sort of specialized scrubbing tool. Cutting a paintbrush is a good strategy so you can reach difficult angles. with the long side while scrubbing with the short side.
 
    Lint-free towels like microfiber cloths. should be handy to rub down and dry off your delicate circuit boards. Even with extensive use, this type of cloth does not shed debris. which would be counterproductive as your goal is to remove the. unwanted material from inside the affected devices.
 
   You can also usehousehold appliances such as the oven to accelerate the speed of drying. An oven heating should never used to dry electronics, but after the appliance shut off. the heated environment is a great place to dehydrate any excess moisture. after cleaning. Substituting a blow drier or desk lamp in place of an oven as the catalyst for drying is fine too.
 
    Take similar steps no matter what material has dirtied your circuit board. The device should removed from the environment it has soiled in. disassembled and scrubbed with various cleaners appropriate for each job.
 
Corrosion occurs as devices age. the metal conductors in devices react with their environment to form a layer of iron oxide. called rust, which is a much less conductive compound. You can think of this phenomenon. as the electronics defense mechanism to prevent short-circuiting. While rust is the most familiar form of corrosion, . there are other metals and means of degradation. that also occur in certain circumstances.
 
If a liquid is not dried from a device, corrosion will occur. Corrosion happens when the metal used to pass connections throughout a device. has exposed to environmental oxidants such as oxygen, sulfur and hydrogen. These chemicals found in the air as well as water. Circuit boards exposed to salty air or water. as well as acid leaks from degraded batteries, can cause corrosion. If left unchecked, corrosion can lead to the break of a connection and the falter of a device.
 
The tools needed while handling a corroded device. include common household items, and your company can use careful tactics. that should not prove to be difficult for those in the electronics field. Things you will need include:
 
Baking soda
Distilled or deionized water
Soft-bristled brush
Phosphate-free household cleaner
Lint-free towel
Household oven
Once you’ve gathered the necessary tools and materials. it is time to create your cleaning solution. and prepare your circuit board for restoration.
 
    Create a cleaning solution by using a quarter-cup of baking soda and 1. or 2 tablespoons of water until the mixture is thick in consistency.
Take a photo or make note of the circuit board’s configuration to allow for easy once the cleanup is complete.
Disconnect cables and remove any chips coming from the circuit board.
Dip your brush into the solution you’ve created. and start scrubbing the board to loosen up the corroded areas.
Once you’ve applied the baking soda and water mixture to all the affected areas, allow 20-30 minutes for. it to dry on the circuit board.
Rinse off the circuit board with distilled water. and ensure all the remaining dried baking soda cleaned off. Using a separate, wet brush may assist you if there’s any trouble with this process.
Use your phosphate-free cleaner such as Clorox or Lysol to spray the entire surface. and allow it to sit for about 15 seconds
.
scrub the board again with your clean toothbrush, rinse it off and then dry it with a lint-free towel. Instead of wiping it down with a dragging motion. dab the circuit board to ensure you don’t cause any damage.
Preheat your oven to 170 degrees. Once it’s reached the desired temperature, turn it off, then place the circuit board within. Leave it there for around three hours to dry any moisture left over by your cleaning process. You may want to take it out sooner or leave it in longer depending on your oven and device.
Reassemble your circuit board and test it to verify its functionality.
If your PCB is still not performing and corrosion is still evident. try using an eraser to eradicate the rest of the mess. This method is particularly effective when the corrosion has accumulated on copper.
 
Use eraser to clean circuit board
 
A liquid such as water, industrial substances. and more often find their way into electronics. Contact with such liquid does not have to mean a total replacement. if you follow a proper cleaning procedure. Things you will need:
 
Container
90% isopropyl alcohol
Distilled or deionized water
Soft bristled brush
Blow dryer/desk lamp
 
   The first steps for how to clean a circuit board that has exposed to water involve basic safety. and straight-forward methods for extracting any moisture within the device:
 
Disconnect the device before handling it
Turn off the device
Rotate and shake the device to drain fluid
Remove battery
Disassemble what you can of the device to further allow water drainage.
If your equipment still experiences issues, cleaning the circuit board itself comes next. Follow these steps:
 
       Completely disassemble the device. Disconnect all cables and open connectors. and remove shields to gain complete access underneath the circuit board. Place your circuit board in an sized. vessel with enough 90% or higher isopropyl alcohol to submerge. it after removing any external technology. If you are unable to find such a high concentration of isopropyl alcohol at a local drug store. or pharmacist. using deionized or distilled water as a slower drying alternative is sufficient.
 
    Once you’ve removed your device from the cleaning solution. use a soft-bristled tool such as a toothbrush or paintbrush to remove any leftover grime. Be sure not to brush to avoid damaging the circuit board. If your company has access to an ultrasonic cleaner, utilizing this specialized tool. enables you to clean hard-to-reach places your basic bristled tool cannot reach. such as connectors and ribbon cables or underneath chips.
 
       After you’re done scrubbing, place the circuit board. underneath a hairdryer set to cold or underneath a desk lamp to. completely dry out any leftover moisture from the cleaning solution.
Examine your board for any signs of the offending liquid. that may remain and check to see if there’s any disfiguration or change in color to the battery. If anything looks out of the ordinary, dispose of the battery and replace it.
Reassemble the device and check to see if it’s working . The battery, LCD and logic board are the most common components to fail upon liquid exposure. so examine these first.
How to Remove Solder Flux From PCB
 
     Soldering occurs when two metals fuse using a heated metal with a low melting point. that binds the two pieces together like glue. Flux is necessary for soldering to protect joints from metal oxides. that inhibit a proper solder job. It does so by converting the metal oxides into salt and water that become locked in the flux once it hardens

Solder flux can accumulate with a tainted yellow crust. on the pins of chips where soldering has occurred. This issue is most common when a circuit board was not handled but is also an fixable issue. What you will need:
 
Soft bristled brush
90%+ anhydrous/rubbing alcohol
Lint-free towel/microfiber cloth
Wet Your Brush to Clean PCB
 
     Wet your brush with rubbing alcohol and scrub the circuit board . with your brush until the solder flux begins to disappear. Once you’re satisfied with the look of your circuit board, dab it with a small towel or microfiber cloth. If your company has access to anhydrous alcohol. or a commercial cleaner for flux and grease removal, this can speed up the process. But.  substituting these products for a high percentage rubbing. alcohol is the more affordable solution.
 
     Keep Your Electronics Functioning With Regular Cleaning or Repair
     Understanding the different methods of how to clean a circuit board depending on. what sort of grime has accumulated on your device is important, as clean boards. can increase efficiency and productivity. Most strategies for getting rid of unwanted gunk involve common products. most plants already have. removing grime and restoring industrial equipment. or other devices is not a difficult task once you understand the steps involved.
 
 

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