Frequently Asked Questions
DJ MicroLaminates’ customer support group has received questions from a wide variety of customers.
We have taken frequently asked questions and formed a FAQ that is divided into six categories:
Frequently Asked Product Questions
A photoresist is a light-sensitive coating in the form of a liquid solution in a volatile solvent or as polymer sheets or rolls which are applied to a substrate or surface, such as silicon, glass, copper, gold, or other rigid materials. Features are created in these films by pattern-wise illuminating the photoresist film which then reacts to actinic light exposures.
For SUEX® films the photoresist will remain in the areas that were exposed to actinic light and dissolves during development in areas that were not exposed to the light. DJ MicroLaminates' photoresists also have adhesive qualities that allow MEMS and other component features to be structured on a wide range of different substrates.
SUEX is the name of DJ MicroLaminates’ product line of both thick and thin epoxy dry film sheets and ADEX is the name of a similar line of thin dry film rolls and sheets. Both lines consist of photo imageable solid resin blends uniquely designed for fine, permanent solid resin parts, plating of metallic microstructures, wafer level packaging, microfluidic structures and MEMS applications. The sheets consist of catatonically cured, modified epoxy photoresist films of varying thicknesses between two throw-away layers of removable protective polyester (PET) film. This epoxy photoresist formulation contains an antimony-free photoacid generator (PAG) and is prepared under a highly controlled solvent-less coating process that provides highly uniform coatings.
This solvent developed negative working photoresist is sensitive to UV radiation in the range of 350 – 395nm.
SUEX sheets are available in thicknesses from 20µm to 1mm and the ADEX sheets and rolls are available in thicknesses from 20µm to 75µm and both are pre-cut to standard wafer and panel sizes for lamination to flat substrate surfaces. The laminate substrates are easy to prepare and ready for lithographic processing in minutes.
Based on a study of customer orders:
- The standard thicknesses of Thin SUEX sheets are 20, 30, 40, 50 and 75 µm (microns)
- The standard thickness of Thick SUEX sheets are 100, 125, 150, 200, 225, 250, 300, 350, 400 and 500 µm
Thick SUEX sheets are are not available in roll form.
- The standard thicknesses for ADEX sheets and rolls are 5, 10, 20, 30, 50 and 75 µm
Custom thicknesses of Thick SUEX sheets up to 1mm are available upon special request
Unexposed SUEX and ADEX sheets are transparent, but after processing they range in color from yellow to yellow-brown. (The higher the process temperature, the greater the tint of brown on yellow.)
Round/wafer cut or square: 46/48, 72/73, 96/98, 146/148, 196/198 and 296/---.
Square, rectangular or custom from 98mm to 298mm sq. and up to 350X500mm flat sheets.
The shelf life of SUEX and ADEX sheets is one year from the date of shipment.
Generally – given your process and environmental conditions – you can continue to use it for a longer period of time.
SUEX and ADEX sheets should be stored in the original black packaging in a standard, temperature-controlled environment between 18°C (65°F) to 25°C (77°F).
ADEX can be stored as a roll at the same temperatures.
We recommend you do not precut SUEX and ADEX sheets nor ADEX rolls.
DJ MicroLaminates will send you sheets which are pre-cut to your specifications. High precision laser die-cut sheets are available upon special request as well as unique shapes and sizes.
If you have to cut the sheets, we recommend that the sheets and cutting tool be heated to 50˚ to 60˚ C. See our cutting instructions for more details.
Frequently Asked Pre-Processing Questions
There are many high-quality laminators on the market that you can choose and get the results you seek. Check out Amazon.com in the US and many countries, or an equivalent site in your area.
We suggest you use a laminator that controls: (1) temperature, (2) line speed (3) temperature control and pressure uniformity, and (4) provides a 3mm jaw opening.
SKY laminating machines have proven to be some of the strongest and most reliable laminators we have tested. The SKY 335R6 Laminating Machine is the most appropriate in their product line. (Available at Amazon.com and other online resellers.) Calibrate the roller temperature on the laminator prior to operation.
No, the sheet cannot be placed on the warm hot plate as it will stick to the substrate and trap air between the SUEX or ADEX and substrate. Air is permanently trapped in this manner.
The sheet cannot contact the substrate until just before entering into the jaw rollers. It is recommended you hold the top sheet up away from the bottom sheet until forced onto the bottom sheet by the top roller to minimize trapping of the air
We recommend that you view our online video to get more information about the lamination process.
Substrates should be free of organic contamination and metal oxides prior to lamination. This may require further cleaning and surface activation prior to dehydration bake and lamination. Cleaning and drying of substrates is recommended immediately prior to lamination. For copper, gold, etc. see special treatment recommendations. Polish glass surfaces with a polishing compound then thoroughly remove the polish until water evenly wets the glass surface.
Chemical adhesion promoters are typically not useful.
SUEX and ADEX adhere to the following substrates: Silicon, Silicon Oxide, Silicon Nitride, Copper, Gold, Aluminum, Titanium, Stainless Steel, Glass, Polymer Composites, other metals and metal oxides. They adhere to silicon and composite materials the best. Gold is particularly poor and copper and glass surfaces are difficult but with proper pretreatment can work well. Copper will require a weak acid etch followed by neutralization with 5% NH4OH. Glass will require treatment with a polishing compound and rinsing until DI water uniformly wets the glass surface.
The aspect ratio increases with the thickness of the film. The aspect ratio is 4:1 for 10µm films. The aspect ratio is over 20:1 for 200µm films and above.
Frequently Asked Processing Questions
No, the two sides of the cut sheets are different.
For SUEX sheets one side appears clear and glossy and the opposite side is hazy. The hazy side contains a thin submicron anti-stick coating which allows for easier handling of the stack of sheets. The PET from either side can be removed first, but it is best to consistently remove the same side before proceeding. We generally recommend removal of the clear sheet first as it visually shows that a PET sheet is still attached to the SUEX layer. This limits the potential to expose the film with the PET still attached.
For ADEX sheets the two sides look the same but are different.
For lamination we recommend placing the substrate on a semi-rigid carrier such as a thicker, 150um (5mil) PET film or better, or better, a 500um aluminum sheet in a cleanroom environment. Place the substrate on the carrier sheet and remove the PET when ready to laminate. Remove the clear PET cover sheet from the substrate immediately prior to lamination. Lay another 150um (5 mil) PET on top of the substrate leaving 3-5mm of the substrate uncovered just ahead of the lamination rollers. Leave the back end of the PET hanging out behind the substrate.
Laminate the SUEX sheet to the substrate on a hot roll laminator by slowly pushing the carrier sheet with the substrate covered by the top PET film into the jaws of the roller. Grab the top PET once within 1cm of the rollers without letting the top PET pass into the rollers. Do not allow the sheets to contact substrate until immediately (<1cm) in front of the rollers. Once the entire substrate and SUEX sheet have passed into the rollers the top PET can be removed. Once the laminated substrate has passed through the laminator it can be carefully removed and placed in a carrier to cool. Do not cool on a cold surface. Films of up to 650um thick may be coated with this process.
The recommended conditions for hot roll lamination are:
|Temperature:||60 - 70°C for all thicknesses|
|Pressure:||5 – 10 psi (30 – 65 kPa)|
|Speed:||0.5 – 1.5ft/min (0.15 – 0.5m/min)*|
A post-lamination bake is normally not needed or recommended for improved adhesion.
For improved surface quality of the SUEX or ADEX sheet after lamination, the laminated article may be baked on a hotplate at 80 - 85°C for 5 minutes.
After the PLB bake the remaining PET film should be left on the SUEX film as the substrate cools to room temperature to protect the resist surface from scratches and dust until use. Remove just prior to exposure.
Frequently Asked Optimization Questions
The use of an anti-stick coating on the mask will minimize sticking of the mask to the SUEX layer during exposure.
For optimum resolution i-line cut-off filters, soda lime glass masks or a piece of soda lime glass placed on top of the mask are highly recommended to remove wavelengths below 350nm. This provides for improved resolution and sidewall acuity. The dose will vary depending on resist thickness, substrate, process and other requirements. See Table 1 for estimated doses on silicon.
“Wafer Bow” is the result of the difference in stress between the cured SUEX layer and the substrate because the resin film has shrunk during cure but also has been firmly attached to the wafer. If the stress is too high the SUEX will delaminate from the substrate leading to defects. This stress is caused by the shrinkage of the resist film during the PEB and the rate of cooling after the PEB. SUEX and ADEX films will bow after cure but adjusting the process conditions can minimize this. Stress can be reduced, but not eliminated, by using a lower PEB temperature, conducting the PEB in an oven not on a hot-plate, and slowly cooling the PEB’d cured SUEX coated substrate to under 50C over at least 3-5 hours, preferably overnight. The slow cooling is highly effective but not always sufficient depending on the adhesion of the SUEX to the substrate, which is dependent on the substrate material (see the Pre-Processing Conditions section above).
Adhesion is dependent on the substrate used, the surface preparation of the substrate, the film thickness, and resist process conditions as noted above. We can provide additional recommendations to improve adhesion to various substrates.
There are several possible explanations for bubbles or voids appearing in the sheets.
We recommend viewing the video included with this FAQ. We also recommend reading our SUEX and ADEX data sheets to learn more and if these explanations and the process steps that do not apply.
Finally, if you other questions, please call our customer support group.
A post-develop bake is good generally but not necessary.
We recommend a bake and cool to increase resolution.
Frequently Asked Development Questions
Exposed wafers may be held in a closed container for a week or more but not after the PEB. The stresses in the exposed section will distort resin in the unexposed areas leading to cracking and delamination of the exposed features.
Preferred process conditions are: develop at room temperature using a two bath PGMEA (propylene glycol methyl ether acetate) system, face down on a wire screen with mild or no agitation. Develop for approximately 2/3rd of the time in the first bath and 1/3rd of the time in the second, cleaner bath. Develop times for best resolution are shown below:
Process Conditions for Thick SUEX TDFS on Silicon Wafers
|UV Filtered Dose,|
mJ/cm2 @ 365 nm
|No UV Filter Dose,|
mJ/cm2 @ 365 nm
|Devl Time Face Down, min||35(20 + 15)||50(30 + 20)||60(40 + 20)||75(50 + 25)||100(70 + 30)||140(100 + 40)|
Our recommended development process is to place the exposed and PEB’d substrates face down on a stainless steel wire screen in a developer tank sufficient to cover the the substrates completely with developer. Very gently agitate the developer solution with a small magnetic stirrer or on an orbital mixer. After the first cycle quickly rinse with a small amount of fresh developer and move the substrates to the 2nd tank. Remove the substrates from the 2nd bath and rinse the developed wafer with isopropyl alcohol, then immerse in clean IPA for 1 to 5 minutes. Remove and place in a warm, not hot oven to dry.
Thin SUEX sheets should be processed in the same manner as thick SUEX except reduce the exposure dose and develop times.
Process conditions for Thin SUEX TDFS on Silicon Wafers
|UV Filtered Dose,|
mJ/cm2 @ 365 nm
|No UV Filter Dose,|
mJ/cm2 @ 365 nm
|Devl Time min||35(20 + 15)||50(30 + 20)||60(40 + 20)||75(50 + 25)||100(70 + 30)|
Frequently Asked Post-Processing Questions
If desired, bake at 125°C/60 min, 150°C/30 min or 150°C/15-20 min. A 200°C hard bake for 30 – 60 minutes is required to remove all volatile components from the film.
Oxygen plasma cleaning is frequently recommended to remove contamination and prepare the surfaces for electroplating.
SUEX is compatible with acid copper, tin/lead, tin, nickel sulfonate, most lead-free electrolytes, and acid gold plating baths.
SUEX and ADEX are normally used as a permanent, highly cross-linked film and is not intended to be removed.
For films that have not been hard baked, an NMP based remover may lift the film from the substrate. Hard baked films are readily removed using laser ablation equipment.
SUEX and ADEX are a non-hazardous, non-regulated material.
Your disposal of SUEX and ADEX as waste is in accordance with your local, state and federal environmental regulations