LTCC PROCESSING INSTRUCTIONS For Ferro A6 and L8 Tape

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4. Through cavity with stepped walls. One other type of cavity has been produced and is a major problem to control. This cavity has a floor that is not at the bottom of the laminate, i.e. the cavity bottom is only supported where it joins the walls. At Ferro Electronic Materials the preferred approach to cavity formation is to punch the cavity layers before any metallization steps (vias, conductors, resistors). Because punching is used cavity geometries are limited to rectangular shapes with rounded corners. It must be recognized that removal of much of a tape layer for cavities can seriously weaken the green sheet and cause difficulties during subsequent processing. One approach to overcome this problem is to punch the tape cavities after metallization. Frames for this have been produced by UHT. Results using this method at Ferro Electronic Materials have not been good because alignment of vias were never as good as with the single punching step. PROCESS STEPS 1. Punch each layer of tape. This punching will make both via holes and cut out the cavity. 2. Fill vias. 3. Print conductors. 4. Print cofiring resistors. 5. Stack layers on registration fixture. 6. Put inserts in cavities (see below for inserts). Do not use top plate. 7. Vacuum bag. 8. Laminate. 9. Remove from vacuum bag and remove from registration fixture. 10. Remove inserts. 11. Trim part to size. 12. Fire. Some of the above steps may not be necessary, e.g. some layers may have no vias. INSERTS Inserts are essential to prevent the cavities from distortion during lamination. At its simplest this distortion will result in rounded cavity wall edges. At the most extreme, cavities will tend to close up and the bottom of the cavity will lift. The through cavities are easiest to deal with. Here inserts can be made from hard materials that can be machined to give a good fit. With other types of cavity the Ferro Electronic Materials preferred material for inserts is Silastic J RTV from Dow Corning. These inserts are made by preparing a dummy part with cavities but
no metallization, etc. Only minimum pressure is used to laminate this dummy part to avoid any cavity distortion. With Ferro Tape, 1000 psi has typically been used. Once the dummy laminate has been prepared, the Silastic J is cast in the cavities and allowed to cure. After curing, the inserts are removed and cleaned and are then ready for use. Other materials that can be used for inserts are pieces of latex and other soft rubber. Latex must be accurately cut to size however. STEPPED WALLS It is important to understand that a major problem can arise with stepped walls. This occurs if inserts are too stiff and do not compress enough during the lamination step. Consequently the steps can receive greater or lesser pressure than the bulk of the laminate and during firing shrink at a different rate. A similar effect can occur with cavity bottoms if a top plate is used on the registration fixture that over compresses Silastic J or latex. 1.13 LAMINATION Lamination may be carried out in either isostatic or uniaxial laminators. However, lamination is critical in achieving consistent green density, and hence consistent shrinkage, hermeticity and electrical performance, and Ferro strongly recommends the use of isostatic lamination, which has been demonstrated to give the most consistent results. Recommended lamination conditions are a pressure of 3000 psi, a temperature of 70°C with a 10 minute dwell time –no pressure followed by a lamination time of 10 minutes. Ferro will provide Lamination Pressure vs. Lamination Density curves for each lot of Ferro Tape as a reference guide for processing. 1.14 BURN-OUT / FIRING Organic burn out may be combined with the firing operation in both box and tunnel furnaces, or may be performed as a separate step. The unfired laminates are heated, on their setters, at a rate of 2°C/minute to peak temperature of 450°C, which should be maintained for a minimum of 2 hours, to ensure complete combustion of all organics. This burn out procedure should be considered a starting point, although it should be more than adequate for most requirements; fine tuning of the burnout procedure will depend on part size, number of layers, and amount of metallization.
Page 1 and 2: 1.1 UNREEL TAPE LTCC PROCESSING INS
Page 3: ased stencils. A vacuum pull throug
Page 7 and 8: L8 Tape Burn out & Firing Profile B
Page 9 and 10: LTCC DESIGN RECOMMENDATIONS 2.1 CON
Page 11 and 12: 2.2 GROUND AND POWER PLANES IC Bond
Page 13 and 14: 2.4 ELECTRICAL VIAS Electrical via
Page 15 and 16: Thermal Hexagonal Via Pattern: Six
Page 17 and 18: Resistor to conductor termination o

LTCC PROCESSING INSTRUCTIONS For Ferro A6 and L8 Tape

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