Essentially, Coverlay and Solder Mask are two applications that are incorporated into the Flexible Circuit’s outermost layer. Although they are similar in application, they have different properties, characteristics, and purposes. Thus, it is crucial to fully comprehend their usage.
In addition, one of these two—Coverlay or Solder Mask—can be utilized as a barrier of defense. However, they have specific capabilities that are beneficial in various operations.
Consequently, in this article, we’d like to dissect the definition of Coverlay and Solder Mask. Additionally, we’ll mainly tackle their difference, design factors, color selections, and thickness.
What is a Flexible Coverlay?
Typically, the fundamental responsibility of a Flexible Coverlay is to protect the external surface of the Flexible PCB or the circuitry. In a similar sense, its function is quite identical to the Flexible Solder Mask; however, it has a definite distinction from each other.
The necessary aspect of elasticity and longevity that a Flexible Coverlay contributes to the Flexible Schematic sets it apart from Solder Mask. Thus, if the application calls for significant versatility; then, one should incorporate a Flexible Coverlay that will encapsulate the copper foils and cables. Further, it offers exceptional flexibility with outstanding dielectric strength.
Even if it is way versatile, it still offers a stable, durable, and reliable solution to Flexible PCBs. In terms of structure, it consists of a single piece of material split into two components: a polyimide, and a bendable glue that has an acrylic or epoxy basis. Moreover, a sealed bendable circuit is created by adhering polyimide to it. It is also positioned in a particular temperature and pressure environment before being oriented to the circuit’s interface.
In-Depth Details of Flexible Coverlay
What is a Flexible Solder Mask?
Flexible Coverlay and Flexible Solder Mask both have the duty to safeguard the circuit board’s outer contact from outside impurities. The Flexible Solder Covering can be used on pitch components, as opposed to Flexible Coverlay.
One of the definite distinctions between the Flexible Solder Mask from Flexible Coverlay is the application; the Solder Mask is commonly applied in the Rigid or Stiff sections of the board. While the Flexible Coverlay is widely applied in the Versatile or Flexible areas of the board. However, it is possible to apply the Coverlay in rigid sections given with particular restrictions.
In terms of positioning, the closest trace distance a Flexible Coverlay could be at 3 mils. While, in Flexible Solder Mask, the minimum trace distance must be at 4 mils since it may experience non-recording concerns if it follows the same specifications as Flexible Coverlay. Last but not least, the substances used in a Flexible Solder Mask are liquid-based, in contrast to Flexible Coverlay, which requires the existence of adhesive and polyimide.
Do-It-Yourself (DIY) Solder Mask Application
Difference Between Solid Sheet Coverlay and Liquid Epoxy Solder Mask
In contrast to Flexible Solder Mask, which is an epoxy-based substance that has been converted to a rigid structure, Coverlay is a concrete layer of polyimide.
Comparison of Solid Sheet Coverlay and Liquid Epoxy Solder Mask
All of these can significantly affect certain factors mentioned underneath.
- Processing of the Components
- Understanding of Precise Intonation SMT and PTH Capabilities
- Characteristics of Electrical Shielding
- Applications and Specifications are much more Stringent
- Consistent Fortitude and Dependability
- Ultimately, Adaptability
Among all the shielding components out there in the industry, the Flexible Coverlay is the widely preferred option that is possible because of its neutral brown color that can perfectly blend with the Flexible Circuit.
A consistent band of polyimide with an impermeable barrier that has the same 0.001-inch dielectric electricity impedance as polyimide flex cores is what it is in principle. In terms of functionality, it serves as an impenetrable shield and is obtainable in an array of widths to satisfy stringent minimal curve specifications. Likewise, this material is covered in a layer of flexible epoxy or acrylic adhesive, which is then attached to the flexible circuit’s body under intense heat and pressure to create a long-lasting link.
Simply put, the elements that comprise the Flexible Solder Mask are identical to the epoxy-based materials employed on Rigid and Rigid-Flex PCBs; however, it has an additional component on it, a Flexible Agent. Applying, photographing, and developing it, in the same manner, results in the required SMT and PTH openings. Over the main core, the diameter is restricted to ¾ to 1 mm, but it will decrease over the top of the lines. Its irregular breadth prevents it from acting as an impregnable barrier and prevents it from providing the same level of electrical impedance.
Design Factors for Flexible Solder Mask and Coverlay
As previously mentioned, both a Solder Shield and a Coverlay are capable of a plethora of different tasks.
Flexible Coverlay
Since Coverlay is a full material constituent, all SMT and PTH openings must be physically drilled using puncture and pin tools, laser engraving, or molding. This constrains the minimal number of apertures and the lowest network of substance that can be kept among consecutive gaps, along with the requirement to bond the Coverlay towards the cord.
A thorough overlay may not be possible because of the restricted quantity of glue and the ease with which exceedingly tiny Coverlay fibers can be fractured or harmed all through production. Additionally, a tiny quantity of glue may ooze out into Coverlay holes. Further, the Coverlay design guidelines that emerge are very distinct from the solder shield conceptual models.
Flexible Solder Mask
Flexible Solder Cover provides nearly similar options to rigid Boards because it is a liquid that has been photo-imaged. All components experience comparatively higher typical openings because of the larger material physical constraints that are specific to polyimide flexible compounds. In addition, it usually does not require the ganging of numerous holes into a single big aperture for configurations with fine-pitch constituents.
Restrictions
One of its limitations is the inability of supplements on the Electromagnetic Interference and Radio Frequency Interference barrier layers to covalently bind to the Solder Mask. It has reduced adhesion capacity. Therefore, if solder shielding is needed in the area where stiffening is also required, a PSA must be used to join the stiffener. For areas with multiple levels of defense, a Coverlay is inevitably necessary.
Coverlay and Flexible Solder Mask: Thickness and Color Selections
Variations for both the polyimide surface of Coverlay and each pre-attached adhesive component are available. The thickness of polyimide is typically between 0.5 mil and 2 mils, but about 1 mil is the width that is most frequently used. On the contrary, the highly utilized glue layer is around 1 mil to 2 mils; however, if planning to have the thinnest option, one could opt for the 1 mil. Additionally, the required adhesive thickness depends on the thickness of the copper to which it is to be attached.
Several Color Selections
As a general rule, 1 millimeter of adhesive is typically needed for every ounce of copper. As an illustration, if the application necessitates 3 ounces of copper, it must be paired with 3 mils of glue. In order to accomplish a suitable encapsulation free of gaps, it is essential to verify that there is sufficient glue to completely encase the underpinning circuits.
After bonding, the covering of the gaps between the circuits consumes a sizable part of the glue thickness, culminating in a structure that is narrower than the cumulative intrinsic physical widths. Over the lines, the polyimide sheet is unaffected and keeps its entire width.
Usually, the solder screen is between 0.7 and 1 micron thick, but it will be thinner around the apparatus. Given that the liquid is applied and then moves into the gaps between the lines, this is comparable to stiff board manufacturing.
Additionally, Flexible Coverlay is available in a variety of colors, including black, white, and light brown. However, the commonly used color in every application is neutral, which is brown color. On the contrary, Flexible Solder Mask comes in several colors as well, some of the common ones are green, blue, yellow, white, transparent, and many others. Nevertheless, the highly utilized color is green.
Discretionary Employment
In configurations where neither substance satisfies all of the operation design criteria, stiffer curve needs, and high-density constituents can occur. One frequent method of resolving this is to apply all materials carefully where and when necessary; making it possible to make use of every substance’s finest quality. Coverlay would be useful with large pitch components and buffer layers in areas that are prone to distortion. Nevertheless, Adjustable Solder Cover would be perfect for areas with that many constituents.
Selective Application
The Coverlay is positioned first, accompanied by the solder stencil with a slight excess onto the Coverlay, to prevent any gaps in the combined layer. In this method to ensure a reliable and useful design that meets requirements, the flexibility supplier’s participation will also be necessary. This move must be performed away from areas of the design that require tight curves due to the chance that a significant strain accumulator will be produced by the conversion from Coverlay to Solder Mask combined with the surplus of the constituents.
Summary
Generally speaking, Flexible Coverlay or Flexible Solder Mask can be used to safeguard the circuit board’s exterior contact; even so, there are some situations where Coverlay isn’t an appropriate solution and conversely. Hence, we have covered all of the crucial information in this blog post one must know in selecting between these two materials.
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