The PCB Evolution
Until the 1970s, almost all electronics were built from individual components, using labor-intensive assembly of thousands of separate diodes and transistors. The miniaturization demanded by the space race led to the first computer chips called “through-hole” circuit board designs. The first through-hole components made their commercial application introduction in the late 1960s. The integrated circuits were embedded in the black plastic housings of the “chips” and the circuits were connected using their long metal legs. The defining physical feature of a through-hole PCB are the “legs” that protrude from the sides of the components and go through the actual circuit board. During assembly, a technician solders the legs (16 to 20) into place, creating the hundreds of electrical connections that make the device “smart”. The chips have a high “stand-off” from the board allowing heat to escape. The high stand-off also allows better cleaning since the cleaning fluid flows under the high-mounted components to dissolve and rinse away contaminants.
Surface Mount Designs
The late 1980s saw the evolution to the first “surface mount” components. These designs retained the legs along the perimeter of the earlier generation chips. But they were smaller and more numerous. They also eliminated the space-wasting holes going through the actual PCB. Surface mount technology (SMT) kept the same basic design as through-hole chips. But it miniaturized all the pieces. By miniaturizing the legs and using all four sides of the chips, the number of electrical connections increased to up to 200 or more on the densest designs. This made them extremely powerful. Shorter legs with tighter stand-offs were more vibration resistant. It also enabled more chips per-square inch.
Ball Grid Array Introduction
By the end of the 1990s, ball grid array (BGA) components became commonplace. BGA components evolved away from space-wasting legs. All electrical connections are under the chip, using micron-sized points of solder to complete the circuits. BGA designs also increase exponentially the number of connections made, since the number of possible connections is limited by the area of the chip, not the perimeter.
Initially seen as microprocessors in computers, BGA components packed still more transistors into the smallest possible package. Each chip supported thousands of tiny solder connections. This made them rugged, even in harsh environments. BGA designs have stand-offs measured in microns, but they make for smarter electronics.
The Appearance of Fiber Optics
In the 2000s, fiber optic components started to appear on PCBs. Almost every fiber network running to a home or business is connected at each end to printed circuit boards using fiber optic transceivers. These are tiny devices mounted on the PCB. They take the optical signal and convert it to an electrical pulse. Fiber optic components are vulnerable to many types of contaminants. These include dust and fingerprints that must be cleaned with specialty tools using special care.
The Rise of 3D Printed PCBs
Today, 3D printed components are gaining popularity. They offer flexibility and versatility in PCB designs that were not possible before. Ideal for quick PCB prototyping or for producing custom circuit boards, 3D printing allows engineers to create curved circuit boards or shapes other than a flat surface. A 3D printed circuit board typically uses a mixture of materials for construction. One material, such as plastic, to 3D print or extrude the board itself. And another material, such as copper or silver paint to serve as an electrical conductor.
Evolving Regulatory Demands
Regulatory and safety requirements are also changing PCB manufacturing and cleaning methods. Many countries have federal, state and local environmental rules limiting the use of ozone-depleting and global warming substances. Also, low toxicity and worker safety are of upmost importance. PCB cleaner formulations are evolving to meet these requirements. They must clean well, meet emerging regulations and be safe for both workers and the environment.
Modern Cleaning for Modern PCBs
PCBs have gone through many changes over the decades and cleaning fluids and methods need to keep pace. Increased package density, the introduction of new materials and more stringent environmental and safety requirements makes cleaning modern PCBs a challenge. Fortunately, there are cleaning fluids and methods to help. Here are some examples.
Low Clearance Components
During soldering, salts are produced as the flux activators are heated. This leaves microscopic crystals behind. These salt crystals sometimes appear on the PCB as a white residue which can be difficult to remove. But if the salts are not cleaned from the PCB, they can corrode the solder joints causing the PCB to fail. Making matters worse is that today’s densely packed PCBs run very hot. This extra heat speeds the corrosive activity, resulting in even more PCB damage. The stubborn white residue usually requires an aggressive flux remover or cleaning fluid to eliminate it. The best flux remover for densely-packed PCBs should be very strong to clean away the salts and other contamination.
Fiber Optic Components
The fiber optic components on a PCB can’t be cleaned with a the same products used on the PCBA itself. A fiber optic strand is smaller than a human hair and the signal it carries is astoundingly fragile. So, cleaning the fiber components must be careful to ensure the speed and the long-term reliability of the entire fiber network.
To clean the fiber components, use lint-free wipes and cleaning sticks that do not leave glue residue or lint on the fiber connectors. For the very best results, use an ultra-pure, water-free cleaning fluid. One specifically engineered for fiber optic cleaning. The fast-drying fluid ensures the wipes or sticks do not leave excessive moisture or residue on the fiber components.
3D Printed or Multi-Material PCBs
When cleaning 3D printed PCBs it is important to take material compatibility into account. 3D printed PCBs are typically made of at least two or more different materials including plastics and metals. Typically, the stronger the cleaning fluid, the higher the risk that it may damage the PCBA, especially plastics.
To Test is Best
A good method to ensure the chosen PCB cleaner or flux remover works without damaging a PCB is to conduct a ‘cleaning trial’ on sacrificial or test circuit boards. Start with a milder cleaner first and try stronger ones until you achieve the optimal cleaning result. Perform tests in more than one area on the PCB to ensure it is safe for all the materials the cleaner may contact.
Some PCB designers conduct their own in-house cleaning trials. But in some instances, you may want to send your sacrificial test circuit boards to the MicroCare Critical Cleaning Lab for an in-lab cleaning assessment. Through cleaning experiments on your PCBs and specific contamination, the lab ensures you are cleaning with the fewest risks to the circuit boards. They may also suggest changes in your cleaning processes to boost PCB cleanliness, regulatory compliance and worker safety.
The Need for Clean Remains
The electronics components from the 1970s have little in common with the advanced microelectronics used today. Changes in layout, materials and safety regulations make modern PCBA cleaning more complex. So, it makes sense that cleaning fluids and methods have also evolved and improved over time. There is a vast array of PCB cleaners on the market. But it is important to choose one that helps you overcome your particular PCB cleaning challenges. The cleaning fluid or flux remover must have the right physical properties to clean well. But it should also be formulated to help protect air quality and ensure worker safety.