Dicing Hard Brittle Materials (1063250)
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Dicing Through Hard and Brittle Materials in theMicro Electronic IndustryBy Gideon Levinson, Dicing Tools Product ManagerA high percentage of micro electronics dicing applications require dicing completelythrough the substrate. While partial dicing is relatively easy, dicing through hard andbrittle materials creates both mounting and quality problems. The following articlediscusses various mounting techniques and quality problems related to the dicing process.Recommendations are made to try solve these problems.Mounting MethodsThe main methods employed in the industry include:Tape mountingWax and adhesive mountingWax and adhesive on carriersMechanical fixturingTape MountingThis is the most common method being used for thin substrates (figure 1).H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g .
c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-8550001Figure 1 - Silicon Wafer on TapeTape mounting is mainly implemented on production lines employing die bondingtechniques after the dicing process. The tape serves as a carrier for both the dicing andthe die bonding process.Tape is used as a carrier in many applications. But the main applications are siliconwafers .005" (0.127mm) up to .025" (0.63mm) thick and hard alumina substrates.010" (0.25mm) up to .080" (2.03mm) thick.
The most commonly used tape is a P.V.C..003" (0.076mm) thick with a combination of P.V.C. sheet and an adhesive applied to thetop side of the tape (figure 2). Thicker tapes are available, up to .010" (0.25mm). Thesetapes are designed for special applications, but they cannot be used on die bondingsystems. This topic will be discussed in more detail later in this article).Tapes are available with different adhesives or what is called "tackiness characteristics."The adhesion characteristics of the most common tapes are 215-315 gr/25mm.Every application should be optimized to determine exact tackiness requirements. Iftackiness is "too low" it can result in loosing dies in the dicing process.
If it is "too high",it may cause problems in the die bonding process.The following is a schematic flow of the process:a. Tape mounting to round frames (ring or flat type - figure 3).b. Substrate being mounted to the tape (figure 4). In some applications the tape is heatedfor five to ten minutes after the mounting to about 65°. This improves the adhesion.c. Frame is being mounted on the saw chuck (figure 5).H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g .
c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-8550001d. Dicing through the substrate into the tape (figure 6).e. Expanding the tape after the dicing process to separate the die (figure 7).f. Die attaching on a die bonder (figure 8).H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g . c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-8550001Tape Mounting in the Dicing Process - Related Problems andRecommendationsFor the purpose of discussion, we will focus on the most common substrates, siliconwafers and hard alumina substrate.
Other substrates behave similarly.Problem A: Loosening small die during dicing.Recommendations1. Reduce the feed rate.2. Lower the cooling flow pressure.3. Use a tape with better adhesion characteristics.4. Improve mounting technique to eliminate air gaps between the substrate and the tape.5. Optimize tape curing process (heating the tape) to improve wafer-to-tape adhesion.Problem B: Chipping at the bottom of the die when using ring type vacuum chuck(figure 9).1. Chipping at the contact between the wafer and the tape is a well known phenomenawhen using a ring type vacuum chuck (figure 10). The chipping results from internalstress created during the cutting process at the ring vacuum groves.H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g .
c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-8550001RecommendationsChange the ring type chuck to a porous type chuck (figures 11, 12 and 13). The porouschuck will perform with a much more uniform vacuum clamping. This will eliminate thering stress effect.H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g . c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-8550001Figure 12 - Ring type chuckFigure 13 - Porous type chuckProblem C: Chipping and large cracks at the wafer contact with the tape (figure 14)not related to ring type vacuum chucks.Recommendations1.
On silicon application using nickel type blades it is important to cut .001" - .0015"into the tape (figure 15). Cutting less than .001" into the tape can cause an overloadsituation because of contact between the blade edge and the tape adhesion.Overloading the cutting process will create high temperatures, resulting in access tomuch chipping and cracking.2.
Improve your mounting technique to eliminate air gaps between the substrate and thetape.H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g . c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-85500013. On the hard alumina applications using resinoid blades, the chipping cracksphenomena at the contact point with the tap is caused mainly because of high bladewear (figure 16).H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g . c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-8550001Blade wear occurs mainly at the blade edge corners, which become rounded.
This causesa small lip on the substrate at the contact point with the tape. The lip breaks off thesubstrate during the cutting process or during die separating process.Using a thicker tape and cutting deeper into the tape .005" to .010" will eliminate the lipeffect, the die will have a straight edge and the round part of the blade edge will be insidethe tape (figure 17).Cutting with resinoid blades on thicker tapes is an improvement. But the operator stillshould check and compensate the blade wear to eliminate the lip effect. A good methodto do this is by calibrating the cut depth with the HEIGHT SENSOR on the saw. A zerocalibration button is an excellent feature available on All ADT dicing saws (figure 18).The zero calibration button, located outside the cutting area, is programmable through thesaw. This enables height calibrations after any number of cuts, without the need of takingthe substrate off the saw.4.
Improve your mounting technique to eliminate air gaps between the substrate and thetape.5. If possible, change the mounting process from tape to wax mounting. (Wax mountingwill be discussed further later in this article.)H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g . c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-8550001Problem D: Chipping and large cracks on the top of the substrate mainly at the diecorners caused by die movement during the cutting process (figure 19).Recommendations1. Check the tape adhesion.
If not strong enough change tape to a stronger adhesion. Orimprove the tape handling process.2. Slow the feed rate.3. Check blade thickness and blade exposure. Using a thicker blade and a smallerexposure will minimize vibrations and improve the cut quality (figure 20).4. Check the cooling nozzle alignment and the cooling flow pressure, make correctionsif needed. *5. Dressing the blade might be an improvement. A new blade, or a blade after manylinear inches of cutting, does not have sharp diamonds exposed, and could havepowder residue between the diamonds. This will result in overloading the cuttingprocess, and will cause chipping due to high temperatures. *6.
If possible, change to a wax mounting process.* Numbers 4 and 5 are not related directly to the tape mounting but should be checkedbefore making any tape changes.H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g . c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-8550001Problem E: Soft metalizations on the backside of the substrate are not dicedcompletely through (figure 21).
This problem is caused mainly by deflection of the softmetalization in the soft tape. Another problem related to the deflection is a peel-off effectof the metalization from the substrate.Recommendations1. The best way to eliminate this effect is in the substrate design stage. The backside ofthe substrate should be designed with a pattern that will eliminate any softmetalization at the dicing area (figure 22).2. A harder more rigid tape should be used to eliminate the deflection effect.H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g .
c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-85500013. If possible, change to a wax mounting process. The substrate is mounted with wax toa solid glass or lava (or others), which eliminates the deflection effect during theprocess (figure 23).Wax and Adhesive Type MountingWax and other adhesive mounting is a very common method for applications requiringsuperior cut quality especially on very thin and brittle materials.Many different adhesives are used for mounting substrates: various types of epoxy, fastglues, ultraviolet type adhesives, thermoplastic polymers (crystal bond) and others.In this article we will concentrate only the most common method, wax mounting.H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g .
c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-8550001Most wax materials are comprised of natural materials - animal, insect, minerals andvegetable. Some are made from synthetic materials.The large variety of wax products are available in lumps, molded bricks, flakes, chips,powders. They vary in:Melting pointFlash pointSpecific gravityStructureHardnessBrittlenessFlexible and elastic characteristicsSurface characteristics (like dry, sticky, oily, slippery)OthersThe waxes used in the micro electronic industry for mounting substrates usually have alow melting point of about 65°C.
Their mechanical characteristics are such that theygenerally will provide for easy handling, accurate mounting and facile wax removal withvarious solvents.H e a d q u a r t e r s – Advanced Dicing Technologies Ltd.www.adtd i c i n g . c o m Advanced Technology Center, Haifa 31905, Israel, Tel.: 972-48545222, Fax: 972-4-8550001Figure 24 Wax mountingAdvantagesThe main advantage of using wax materials is not the wax itself acting as a superclamping media but the ability to mount a delicate substrate to a thick and flat supportingsubstrate. This substrate provides good support and the ability to make a deep cut into thesupporting substrate.
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