With the advancement of technology, electronic products are becoming thinner and more compact. Consequently, electronic components are also getting smaller, and even the thickness of printed circuit boards (PCBs) is decreasing. The thinnest PCB Workingbear has seen is 0.4mm. Such thin PCBs are prone to deformation or warpage due to the high temperatures result in uneven thermal stress while go through SMT reflow oven, which can even cause components to fall off inside the reflow oven.
Conformal coating is a protective chemical coating or polymer film applied to printed circuit boards (PCBs) and critical electronic components to protect them from environmental factors such as moisture, dust, chemicals, and temperature extremes.
This coating, typically 25 to 300 µm thick, enhances the product’s resistance to moisture, dirt, dust, and chemical contamination. Additionally, it prevents solder joints and conductors from continuing to corrode by blocking contact with air. By incorporating specific ingredients, conformal coatings can also provide shielding against electromagnetic interference and serve as an insulator.
BGA packages are prone to HIP, also known as HoP defects, during the reflow process, and it is an undeniable fact that the larger the size and the more balls a BGA package has, the more likely HIP is to occur. This double-ball soldering defect, Head in Pillow , is a particularly troublesome engineering problem because neither 2D X-ray inspection nor electrical testing (FVT or ICT), and even sending the product to burn-in (B/I), can detect HIP issues with 100% certainty.
In this blog, Workingbear has explored the causes and analysis of soldering cracks and electronic component detachment in several articles. It has consistently mentioned that most of the fractures occurring when electronic components detach happen at the Intermetallic Compound (IMC) layer. This indicates that the most vulnerable part of the overall structure, once the component is soldered to the PCB (Printed Circuit Board), is this IMC layer, hence the fractures occurring at this point.
However, nearly all articles also point out that it is essential to form this IMC layer between the solder paste and the component leads, as well as between the solder paste and the metal of the PCB, for effective soldering, ensuring solder joint strength.
A user asked: “How is the thickness of the stencil determined? What considerations are there for the shape of the stencil apertures?”
The thickness of the stencil is mainly determined by the amount of solder paste needed for component soldering. Thinner stencils usually mean less solder paste deposited during printing. The amount of solder paste required for each solder joint depends on the components on the printed circuit board (PCB), especially those sensitive to solder volume, such as BGAs with the smallest ball pitch and fine-pitch components. Additionally, smaller components demand higher precision in solder paste printed. Ultimately, the decision also depends on the quality of solder joints after soldering.
