#STENCILES FOR ARMY OF TWO MASKS SOFTWARE#

Create your own unique works of art, add some interest to the walls of your home, or even display a new pattern on your clothing. The options are limitless use them on any surface you can think of, with paint, fabric, paper, or any other materials. Our amazing collection includes stencils from various artists, giving you plenty of options for styles and shapes. If you’re dealing with high power consumption, you might be inclined to move toward 80% in order to facilitate heat flow from the thermal pad to the PCB however, this document from Texas Instruments indicates that 50% coverage is adequate even for high-power applications.Welcome to StencilGirl Products, your central stop for stencils for artists! Whether you’re experienced with mixed-media or have just started experimenting with unique stencil designs, we have a wide range of stencils perfect for your needs. In general, the lower percentages are probably preferable simply because they are farther from the risks associated with 100% (i.e., full-pad) coverage. You’re not likely to figure out the “ideal” ratio, but a review of reliable literature indicates that you should aim for at least 50% and not more than 80%. The overall solder coverage (i.e., the ratio of solder area to exposed-pad area, here expressed as a percentage) can be controlled by adjusting the geometry of the matrix-assuming that you know what the overall coverage should be. The following diagram conveys the general idea. The dominant special stencil design is the “window pane” arrangement, also referred to with terms like “pad array,” “cross-hatching,” and “matrix.” This approach allows volatiles to escape without causing mischief and reduces the amount of solder between the PCB and the exposed pad. My guess is that most exposed pads are large enough to warrant special stencil design, but the issue is certainly more pronounced as the size of the exposed pad increases.

One thing to keep in mind before we continue is that the size of the exposed pad influences the risk associated with a full-pad solder-paste application-smaller exposed pads are more like normal surface-mount connections, which of course don’t require solder-paste modifications. If these gases cannot escape in an orderly fashion, they can interfere with component placement and lead to unpredictable solder voids. As temperature increases, volatile solder-paste compounds vaporize in a process known as outgassing. The primary concern with a full-pad solder-paste application is “floating”-an excessive amount of solder between the thermal pad and the PCB can cause the entire component to float above the level at which the perimeter lands can make contact with their pads:Īnother disadvantage of a full-pad application is related to the chemical changes that occur during the soldering process.

Usually this is fine, but with thermal pads, it can be a problem. This means that the paste-mask layer will have an opening that includes the entire pad (minus the specified paste-mask shrink).

#STENCILES FOR ARMY OF TWO MASKS SOFTWARE#

The trouble is, if you use a typical surface-mount pad for the part’s thermal pad, the PCB layout software will treat this pad like any other. The solder-paste issue is perhaps most problematic for designers who 1) have limited experience with exposed-pad packages and 2) create a custom PCB footprint, instead of using an existing footprint from a reliable part library. Another complication is ensuring that the assembly process is not compromised by improper solder-paste techniques. One of these-namely, proper thermal-pad PCB layout-is discussed in a previous technical brief. These packages are understandably popular they are beneficial in terms of form factor (thanks to the low profile and small footprint), electrical performance (i.e., low lead inductance), and thermal performance.Īs usual, though, there are also some difficulties. They carry a variety of abbreviations-e.g., QFN (quad flat no-lead), DFN (dual flat no-lead), MLF (micro leadframe), MLP (micro leadframe package), LLP (leadless leadframe package), LFCSP (leadframe chip scale package). A properly designed solder stencil helps to ensure successful reflow soldering with IC packages that have an exposed thermal pad.Įxposed-pad packages have become quite common.

Stenciles for army of two masks