Tape composition and process for internally constrained sintering of low temperature co-fired ceramic
View Patent ↗The present invention relates to a method to achieve the suppression of planar shrinkage in LTCC ceramic tape laminate structures without externally applied forces or sacrificial constraining tape. The method utilizes a non-sacrificial constraining tape that constrains a tape assembly.
1. A method for reducing x,y shrinkage during firing of a green assembly comprising
at least one layer of glass-containing non-sacrificial constraining tape and
at least one layer of glass-containing primary tape,
wherein the constraining tape and the primary tape are laminated to form an assembly, the method comprising the step of firing the green assembly,
wherein the tape components of the assembly upon thermal processing exhibit an interactive suppression of x,y shrinkage to substantially zero,
wherein the glass in the primary tape exhibits a dimensional change measured in TMA (at 5-gram loading force and 10° C./min heating rate) of about 700° C. or higher,
wherein the glass in the constraining tape exhibits a dimensional change measured in TMA of at least 75° C. lower than the primary tape,
wherein the glass of the constraining tape initiates sintering before the glass of the primary tape and the constraining tape transforms into a rigid form below 700° C. and,
wherein the glass of the constraining tape develops in excess of 50 volume % crystalline phases, and
wherein the glass in the primary tape and the glass in the constraining tape are each crystallizable-glass.
2. The method of claim 1 wherein the primary tape comprises a composition of ceramic filler and glass which upon processing transforms the tape to a rigid form.
3. The method of claim 1 wherein the constraining tape comprises a composition of ceramic filler and glass which upon processing transforms the tape to a rigid form.
4. The method of claim 1 wherein the glass of the primary tape comprises, based on total composition:SiO 2 52–54, Al 2 O 3 12.5–14.5, B 2 O 3 8–9, CaO 16–18, MgO 0.5–5, Na 2 O 1.7–2.5, Li 2 O 0.2–0.3, SrO 0–4, K 2 O 1–2 in weight %.
5. The method of claim 1 wherein the glass of the constraining tape comprises, based on total composition, B 2 O 3 6–13, BaO 20–22, Li 2 O 0.5–1.5, P 2 O 5 3.5–4.5, TiO 2 25–33, Cs 2 O 1–6.5, Nd 2 O 3 29–32 in weight %.
6. The method of claim 1 wherein the glass of the constraining tape comprises, based on total composition, SiO 2 12–14, ZrO 2 3–6, B 2 O 3 20–27, BaO 12–15, MgO 33–36, Li 2 O 1–3, P 2 O 5 3–8, Cs 2 O 0–2 in weight %.
7. The method of claim 1 wherein the non-sacrificial constraining tape comprises filler particles having a bimodal particle size distribution with D50 of the larger size particles being in the range of 1.5 to 2.0 microns and D50 of the smaller size particles being in the range of 0.3 to 0.8 microns.
8. The method of claim 1 wherein the primary tape comprises filler particles having a bimodal particle size distribution with D50 of the larger size particles being in the range of 1.5 to 2.0 microns and D50 of the smaller size particles being in the range of 0.3 to 0.8 microns.
9. The method of claim 1 , wherein the firing step is under conditions suitable for mass production.
10. The method of claim 1 , wherein the x,y shrinkage is less than 0.5%.
11. The method of claim 1 , wherein the x,y shrinkage is less than 0.1%.
12. The method of claim 1 , wherein the x,y shrinkage is less than 0.05%.
13. The method of claim 1 , wherein the ratio of the total thickness of the primary and constraining tape layers to the constraining tape layers is between 19:1 and 2:1.
14. The method of claim 1 , wherein the primary tape is 1 to 20 mils in thickness.
15. The method of claim 1 , wherein the glass of the constraining tape develops in excess of 50 volume % crystalline phases under conditions suitable for mass production.
16. The method of claim 1 , wherein the glass in the constraining tape exhibits a dimensional change measured in TMA of at least 100° C. to 150° C. lower than the primary tape.