Reducing Costs With Longer Print Runs

John Gaudiuso explained how the choice of mesh in screen printing applications could lead to cost savings. This is what was discovered.

Screen printed electronics get increasingly smaller so finer features are required. Cost also becomes important as screens are being used up more due to dimensional issues occurring faster. This is seen more with meshes made from stainless steel because of its deformation properties over print runs.

There are different ways to combat screen dimensional stability and longevity problems whilst also being able to print fine lines. One method is to use a trampoline screen to help improve the longevity of stainless steel mesh. Stainless steel mesh is rigid and has difficulty returning to its original form. Using a trampoline screen allows the cuter mesh (a more elastic mesh-like polyester) to expand more than the inner, more rigid mesh, The outer mesh is more elastic and will return to form more than the more rigid inner mesh, which in turn allows longer print runs. Although this option is a good option, it is still a more time-consuming method to manufacture a trampoline screen with stainless steel mesh than it is to stretch a single mesh onto a frame.

The second option is to use a synthetic mesh such as V-Screen, which has advantages over many other meshes. The mesh is woven with a large open area and a fine thread comprising Vecry fibre; this has a structure made up of a liquid crystal-based polymer core called Vectran, with a sheath of a flexible polymer called Pen. Some important features of V-Screen are its high tensile strength (stronger than stainless steel), almost no plastic deformation during printing, outstanding abrasion resistance, fine line printing and translucent fibres. All these features allow for longer print runs with better edge definitions.

ABRASION RESISTANCE

V-Screen has outstanding abrasion resistance, which is important for the durability of a screen. Abrasion resistance is also important so that the paste being used does not get contaminated with particles from the mesh. If particles from the mesh, especially stainless steel mesh, get .into the paste it is possible to see anomalies in the finished part with variances’ in desired results, so the yield will decrease:

This is seen in stainless steel meshes because of the squeegee giving a rubbing motion across the stainless steel; the repeated friction causes the metal to abrade off the wire thread.

With the larger open areas and fine threads of V-Screen, it is possible to print smaller features such as 50 micron line widths. The smallest feature achieved to date with V-Screen is 30 microns in a laboratory setting using an organic paste. Having larger open areas and fine threads also makes it possible to achieve a better surface roughness value (RZ), which is important for gasketing the screen to the substrate. When a good gasket is formed, less bleeding occurs and straighter printed lines can be achieved. 

STRENGTH MID PROPERTIES

V-Screen’s high tensile strength allows for a stronger mesh with large areas, giving it the ability to stretch to hi tensions which helps in reducing the snap-off distance of the screen, which in turn helps with the longevity of the screen. This feature also helps keep dimensions over long print runs because the mesh doesn’t have to deflect as much to transfer the paste.

V-Screen has almost no plastic deformation during printing, primarily due to its physical properties. Vecry is a synthetic material that has memory, much like a memory foam mattress, while natural materials such as stainless steel do not. After the forces of a squeegee are repeatedly applied to any screen, the screen will begin to distort. However because of V-Screen’s memory, the distortion is minimal. Because of having a higher tensile strength, it is possible to achieve higher screen tension where less snap-off distance is required for printing. Consequently less squeegee force has to be applied to V-Screen when printing compared to screens made with other mesh materials, thus further improving dimensional stability over long print runs.

V-Screen can hold its tensions over these long print runs which allows for virtually no tension loss. Once tension on the screen changes, pattern dimensions begin to change. Holding a tight tolerance is easier to achieve while printing more parts using the V-Screen. Figure 1 shows the dimensional stability of a V-Screen’s dimensional accuracy over 5000 prints.

EMULSION AND ADHESION

To achieve finer screen printing features and good line resolution, the emulsion used is important. Although any emulsion works well with the V-Screen, one emulsion was made specifically to be used with it. The V-i emulsion is a soft emulsion that has great line resolution for fine features. As it is a soft emulsion it has the ability to form over substrates that have varying surface roughness, causing a better gasket which leads to lower bleeding issues.

Translucent fibres allow for better emulsion adhesion. In some other meshes, such as stainless steel, the emulsion does not encapsulate the thread; the V-Screen allows for light transmission through the threads and encapsulates the emulsion around the thread, including on the squeegee side. By encapsulating the thread in the emulsion, the emulsion has a larger area to hold on to during printing, which also helps with longer print runs because the emulsion won’t wear away as quickly. This also helps with creating better edge definitions during printing.

Using the V-Screen it is possible to lower production costs due to the longevity of the screen, whilst its structures give it the ability to print fine lines. V-Screen has a high tensile strength, almost no plastic deformation, outstanding abrasion resistance, line line printing and translucent fibres, all helping to give it a longer life. V-Screen is not going to cure the need to print finer lines than 30 microns, so a trampoline will be a good second option.

John Gaudiuso is an Engineer for Dynamesh.