PCB cleaning – what are various cleaning processes and standards
Cleaning a circuit board is an important step in the PCB-making process. A clean circuit board can help prevent defects in the finish of the boards and mitigate any damage to sensitive circuitry. PCB cleaning can also make PCB look much better, which any PCB designer or manufacturer wish.
What is PCB cleaning?
PCB cleaning is an important part of PCB fabrication. It is a process by which the manufacturer cleans and prepares the printed circuit board surface. They make the board ready to install the components. In the PCB cleaning process, all unwanted particles are removed from the top layer of the board.
The manufacturer uses chemicals that can dissolve organic material, such as grease, oil, and resin, to clean away these contaminants. The PCB cleaning process typically uses solvents such as alcohols or esters. The solvent may also contain surfactants to help reduce surface tension and improve the wetting of contaminants during the cleaning process.
Why is PCB cleaning required?
PCB cleaning helps to:
●Remove oil, dust, and other residues from the PCB surface.
●Improve solderability of PCB surface.
●Improve solder joints’ quality and reliability of electronic equipment.
What are the different PCB cleaning methods?
There are several methods for PCB cleaning:
●Soap and water: It is one of the oldest methods for cleaning PCBs because it’s inexpensive and easy to perform. However, this method isn’t very effective at removing contaminants like oils or greases because soaps are not very good at emulsifying oils or greases (breaking them into smaller pieces). In addition, soaps do not dissolve in water; instead, they form cloudy suspensions that don’t penetrate well into cracks or crevices where contaminants may hide.
●Chemical wash: This method uses a chemical solution to clean the board, which can be effective but will damage surface coatings or components if not done properly.
●Ionic cleaning: This method uses an ionic solution that removes contaminants without damaging sensitive components. It’s ideal for cleaning small areas or edges of boards that have been damaged by solder flux during manufacturing.
●Ultrasonic cleaning: This method uses high-frequency sound waves to remove loose particles from electronic components on PCBs without damaging them. Still, it isn’t suitable for removing solder flux because it doesn’t reach temperatures high enough to dissolve the flux residue as chemical washes do.
What is the main PCB cleaning process?
The main PCB cleaning process uses an ultrasonic cleaner. It uses high-frequency sound waves to break down dirt and other contaminants.
These sound waves vibrate at extreme speeds to clean the surface of a PCB.
Bubbles expand and contract. They push against each other and any contaminants on the board’s surface. These contaminants are then removed from the board’s surface by being forced out of its pores and cracks.
After cleaning, the designers must inspect the boards for any damage caused by the cleaning process. They can use a microscope or magnifying glass to closely examine all sides of the board for scratches or loose particles.
What are the standards of PCB cleaning?
There are different standards for PCB cleaning according to their purpose.
IEC 60286-1 Cleanliness of Printed Boards is one of those standards. It has been formulated by International Electrotechnical Commission (IEC). This standard specifies the cleanliness of unpopulated printed and unpopulated flexible boards.
IPC-5704 Cleanliness Requirements for Unpopulated Printed Boards is another standard that specifies cleanliness requirements for unpopulated printed boards. Both these standards are similar but differ in some aspects, such as IPC-5704 does not cover requirements for flexible boards, and IEC 60286-1 does not cover requirements for flexible boards and rigid boards with conductive patterns smaller than 50mm×50mm in size.
The IPC-6012D standard is similar to IPC-5704 but covers populated printed boards. The standard requires that the PCB be cleaned to a Class 100 cleanroom level. The class 100 level means fewer than 100 particles in the air per cubic centimeter.
How do you clean a PCB after soldering?
PCB cleaning after PCB soldering is very important. It’s not just to make the board look nice but also to ensure that nothing gets shorted out by solder flux and other debris.
There are a few different methods to clean the PCB. The most common is isopropyl alcohol, which is easily available at any drug store or supermarket. Designers can also use Windex or similar products, but make sure to use the same brand for both sides of the board — don’t mix water with ammonia on one side because it will erode the copper traces on the other.
To clean the board, spray alcohol onto it and wipe away any excess with paper towels or an old T-shirt. It’s best not to use paper towels if possible because they tend to leave bits behind that can cause short later on down the road.
What are the typical contaminants in PCB?
Typical contaminants in Printed circuit boards (PCBs) include:
- Metals such as copper, tin, gold, and silver can cause corrosion of nearby surfaces or tracks. This can lead to poor electrical connections between components or open circuits.
- Oxides and silicates form conductive paths between tracks or pads and may short out the circuit if they occur at a critical location.
- Organic compounds can act as insulators between pads and tracks, preventing good electrical contact between them.
- Grease from fingerprints is conductive and may cause shorts between pads and tracks.
Most of these contaminants are present as a result of the fabrication process.
What factors cause difficulty cleaning PCB?
Many factors can cause difficulty in PCB cleaning. The following are the most common ones:
- Poor surface finish.
- Poor solder mask opening.
- Surface contamination or residue from chemicals or other processes.
- Solder mask undercut (undercut is when the solder mask goes under the copper pads on the board).
The PCB cleaning process is crucial to achieving a successful reflow and safe production. Due to the high cost of PCB, improper cleaning methods when fabricating may damage or ruin the quality of PCB after reflow soldering/assembly.
An important thing to remember while cleaning PCB is this—excessive force can destroy the copper traces on the board.