After much testing, BEST has chosen to upgrade its standard SMT stencil material to Tension™ material from Datum™. This material, after 2 plus years in the making has proven to give the kind of printing performance of nanocoated stencils without the downsides of these stencils. A recent study has also indicated that the consistency of the printing performance is even better than nanocoated stencils. This same study, which compared the printing of fine grain stainless, nanocoated fine grain stainless to this new ultra fine grain stainless pointed out that this Tension™ was truly the best giving the most consistent highest paste release volume results. While this 5-8% better volume performance boost may not be warranted on older technology boards, todays’ fine pitch rich boards demand whatever is required to get the yields up. Why would you not use this type of material to improve your process yields.
Cut quality showing smooth walls of ultra fine grain Tension™ aperture at 400X
The downsides of the nanocoating process for improved stencil performance are well-documented. The transfer efficiency of these coated stencils is higher with improvements over the other standard materials of from 3-10%. The downsides of the nanocaoted stencils are also well-documented. First the nanocoated stencils take time to process. This means the nanocoated stencils cannot be delivered in as quick of a time frame. Secondly the nanocoated stencils are wiped off after a period of tie which means that that they need to be recoated. Lastly, extra $20-40 per stencil cost is something that the user needs to bear.
Solder Paste Volume comparison from APEX 2017 Presentation Showing 10% Better Paste Release from Tension™ Material
BEST has now adopted this Tension™ material as its standard material for 4 and 5 mil thick stencils. The cost of this material has forced us to slightly increase our end selling prices by a few dollars. Just a few additional reworks or touchups will more than pay for itself in terms pf rework. We urge you to give it a try.
In some processes such as ion deposition, ion implantation and etching all of which require only certain micro area of the substrate to be processed, shadow masks help define the areas of where processing takes place. Physical vapor deposition processes including but not limited to electron beam vapor deposition, molecular beam epitaxy, pulsed laser deposition and sputtering can all use these shadow masks to control the process. These processes are additive in nature. In the etching process selective areas of a substrate on a very small level are removed in areas where there are “holes” in the shadow mask. In ion implantation chemical sites “dope” the material in the section where the apertures of the shadow mask are while blocking the others. One of the largest applications that is driving demand for shadow masks is the deposition of inks on to substrates to engineer complex electronics components and various products. In these processes the shadow mask, which is a micro machined template, is use to deposit material onto the substrate.
Shadow Mask for CVD Process
Shadow masks define device areas and form micro-structures with precision by masking or covering the target surface. Patterning a silicon wafer or substrate is usually processed with deposition using a photomask or direct-write lithography.
Compared to photolithography, shadow masks are a rapid and cost effective alternative over with feature sizes no smaller than 10um. Laser fabricated geometries in shadow masks achieve smaller dimensions, sharper edges, and tighter tolerances than the traditional chemical etching approach. Laser machining of the shadow mask is a “greener” process not having any leftover chemicals that need to be gotten rid of, In many cases shadow masks can be fabricated from unconventional materials that eliminate possible chemical contamination or reactions.
Mechanical supports or carrier frames can be fabricated to assist in handling and aligning shadow-masks to target device features.
Shadow Mask Applications:
- Optical Devices
- Encoder Disks
- Photovoltaics (solar cells)
- User Defined Masks
- MEMS Devices
- Biomedical Devices
- Alignment Targets
Below are some of the feature sizes of these shadow masks using laser ablation technology.
Laser Machined Shadow Masks-General Guidelines
- Lead time: 24-48 hours
- Material: Stainless Steel, Kapton™
- Max size: 24" x 24"
- Thickness: 0.001"-0.020"
- Smallest aperture size: 0.002"
Shadow mask for etching
CAD or Data Requirements
CAD system integration enable flexible, laser manufacturing from customer-generated data. Although most file types are accepted, the preferred file types include DWG, DXF, GERBER and most other 2D formats.
Chemical Etching vs Laser Machinig
When there are a lot of details to the mask a lot of laser cuts need to occur thereby extending the processing time. Photochemical etching on the other hand etches all of the features at the same time. In general the more complex the pattern the more it favors chemical etching.
The thicker the part the longer the chemical etching process takes. As long as the material requirement is 20 mils or less no processing time is added with laser machining. In general the thicker the material the greater the favoring of laser machining. The cost part of the equation depends on the above factors, namely thickness, part complexity and time. More complex parts means greater laser processing costs. Thicker materials take longer and will likely be more extensive when laser machined.
Call BEST Inc. in order to get a price quotation or to see about micro machining your shadow mask using lasers.