September, 2020
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Page 53
The Parallel Evolution of PCBs and Cleaning Methods
By Emily Peck, Senior Chemist, MicroCare, LLC M
icro components, such as CSPs, flip chips, micro BGAs, and QFNs, are routinely used
in today’s complex and miniature elec- tronics. Low-standoff components, like MOSFETs and zero-clearance compo- nents, are common. I/O counts are
of contaminants, including dust and finger prints. Today, 3D-printed components
are gaining popularity. They offer flexibility and versatility in design and are ideal for quick prototyping or for producing custom boards. 3D printing allows the creation
of curved or unusually shaped circuit boards. These boards use multiple materials as well, such as plastic for
the board itself and copper or silver conductive ink as the conductor.
Changing Cleaning Requirements
PCBs have gone through con-
tinuous change over the decades. Cleaning fluids and methods have evolved alongside them. Increasing packaging density, new materials and stricter environmental and safe-
ty requirements makes cleaning today’s PCBs a challenge. Many countries have federal,
state and local rules that limit the use of ozone-depleting and global warming substances. Also, low toxic- ity and worker safety are of utmost importance. During soldering, salts are pro- duced as the flux activators are heat-
Continued on page 56
BGA components have standoffs measured in microns.
increasing and circuit boards are becoming multifunctional. But, as PCBAs continue to
shrink in size and grow in complexi- ty, cleaning the contamination from them is more challenging. Dirty PCBAs are vulnerable to many long- term performance and reliability problems. These include parasitic leakage, electrochemical migration, delamination, shorting, and dendrite growth.
Electronics Evolution Until the 1970s, nearly all elec-
tronics were built from individual components. This was labor inten- sive and required thousands of sepa- rate diodes and transistors. Minia - turization, demanded by the space race, led to through-hole circuit board designs. ICs were embedded into black
plastic housings. Their legs were sol- dered after passing through the cir- cuit board, connecting them. These chips have high standoff from the board, allowing heat to escape. The height also allows for better cleanli- ness, since fluid can flow underneath the components. The first surface mount compo-
nents appeared in the late 80s. The trend of miniaturization continued. By reducing the size of the legs and using four sides of the chips, the number of connections was increased to 200 and beyond for the densest designs. This made them extremely powerful, more resistant to vibration and allowed more chips per square inch.
By the end of the 90s, BGA com-
ponents were commonplace. A further evolution away from space-wasting legs, all connections are made under- neath the chip, using micron-sized points of solder to form a complete cir- cuit. These designs also exponentially increased the number of connections, since the limiting factor became the area underneath the chip, and not its perimeter. The new millennium brought
with it fiber optic components. Almost every fiber network running to a home or business is connected at each end to transceivers mounted to PCBs. However, fiber optic compo- nents are vulnerable to many types
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