Or what the @#$% is a squircle, and what’s it doing on my stencil?
The time period “squircle” is a portmanteau, or mashup, of sq. and circle. It’s an actual phrase, and the form is often known as a superellipse to supernerds. We jest, however moreover having a humorous title, the squircle is an efficient instrument for maximizing solder paste launch and general deposit quantity.
A squircle (FIGURE 1) is a sq. with rounded corners that, when integrated into stencil aperture designs for small space arrays, offers higher print high quality than both a sq. or a circle alone. It brings one of the best of each worlds to an especially difficult a part of the printing course of.
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FIGURE 1. Aperture shapes examined for switch effectivity, variation and deposit quantity.
In current in depth print testing at AIM’s Juarez, Mexico, purposes laboratory, on a print take a look at car that contained aperture shapes together with squares, circles and squircles, we had been capable of make a powerful case for the squircle as an answer to many print challenges. Evaluating apertures of the identical main dimension (diameter or aspect size) and space ratio, we had been capable of immediately examine switch efficiencies, precise deposit volumes and quantity repeatability of the three shapes.
DfM specialists purport the squircle because the optimized aperture design for advantageous options. Right here’s why:
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Squares. A sq. has the inherent advantage of maximizing the world of an aperture. (It’s why White Citadel hamburgers are sq.: no wasted house on the griddle). When printing solder paste, nevertheless, the particles are likely to agglomerate into sharp aperture corners, leading to extra variation from deposit to deposit. It is usually seemingly this variation will develop over time if the stencil wipe efficacy diminishes and the paste accumulation will increase. Squares inherently have larger volumes than circles for a similar main dimension, so after all they may deposit extra paste, but when these paste-grabbing corners overlap pad edges, additionally they create gasketing issues that may drive excessive variation.
Circles. Circles don’t have any pad-overlapping corners and no paste useless zones, thus eliminating the 2 main points related to squares. However due to their decrease aperture space they inherently print much less solder paste. Moreover, circles have equal floor pressure throughout the diameter of the aperture. Throughout separation, this may occasionally enhance the quantity of solder paste that continues to be within the aperture. Think about a cleaning soap bubble on a flat floor; equal floor pressure retains it steady. This similar attribute discourages paste from exiting the round aperture. A sq., nevertheless, exerts unequal forces that facilitate launch.
Squircles. The squircle combines the volumetric advantage of a sq. with out the paste accumulation or the bigger overlap or of sharp corners that the circle brings to the method. FIGURE 2 exhibits the measured switch efficiencies and calculated coefficients of variation of every kind of aperture. Discover the switch effectivity is barely decrease on the sq. than the circle, however solely by a number of proportion factors. The sq. additionally has barely larger variation on the sort 4 paste, and is equal to the sort 5 paste information. The squircle persistently has the best switch charge, and comparable or decrease variation than the squares or circles.
FIGURE 2. Switch effectivity and coefficient of variation for various aperture geometries with 0.63 space ratios.
FIGURE 3. Deposit volumes for various aperture geometries.
FIGURE 3 exhibits the typical volumes deposited by every aperture form. Word that though the sq. confirmed decrease switch effectivity, its bigger space resulted in larger volumes than the circle. However the squircle deposited the best volumes of all apertures. In all instances, the sort 5 paste persistently produced marginally larger volumes, however not sufficient to justify a transition to it in a manufacturing surroundings the place value, separate storage and reflow points would come up. The variations in volumes, whereas trending persistently, will not be vital for this measurement aperture, which, on this case, was for a 0.4mm BGA, the smallest part footprint on our take a look at board. It’s affordable to anticipate related efficiency enhancements on smaller space ratios as properly.
Word that switch charges are very excessive and variation charges very low in comparison with typical outcomes from related print assessments. These print assessments had been performed below a great surroundings, utilizing a polymer nanocoated stencil. It’s affordable to anticipate related developments in manufacturing environments, however seemingly with decrease switch charges and better variation charges. It is usually affordable to make use of nanocoatings on stencils with tight space ratios due to the (ceaselessly documented) high quality enhancements they supply.
Information collected, however not proven right here, additionally point out the squircle is extra strong towards the results of room-temperature growing old and lengthy pause instances (>60 min.) between prints. Extra information on this research shall be revealed and introduced on the upcoming IPC Apex convention.
TABLE 1. Typical Viscosities of Fluids in Ambient Environments.
Squircle: the hybrid aperture with a humorous title that provides a pleasant increase to advantageous characteristic print high quality. Give it a attempt!
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