Zero Shrinkage of LTCC by Self‐Constrained Sintering

Abstract

Low shrinkage in x and y direction and low tolerances of shrinkage are an indispensable precondition for high-density component configuration. Therefore, zero shrinkage sintering technologies as pressure-assisted sintering and sacrificial tapes have been introduced in the low-temperature co-fired ceramics (LTCC) production by different manufacturers. Disadvantages of these methods are high costs of sintering equipment and an additional process step to remove the sacrificial tapes. In this article, newly developed self-constrained sintering methods are presented. The new technology, HeraLock s , delivers LTCC modules with a sintering shrinkage in x and y direction of less than 0.2% and with a shrinkage tolerance of 70.02% without sacrificial layers and external pressure. Each tape is self-constrained by integration of a layer showing no shrinkage in the sintering temperature range of the LTCC. Large area metallization, integration of channels, cavities and passive electronic components are possible without waviness and camber. Self-constrained laminates are an alternative way to produce zero shrinkage LTCC. They consist of tapes sintering at different temperature intervals. Precondition for a successful production of a self-constrained LTCC laminate is the development of well-adapted material and tapes, respectively. This task is very challenging, because sintering range, high-temperature reactivity and thermal expansion coefficient have to be matched and each tape has to fulfill specific functions in the final component, which requires the tailoring of many properties as permittivity, dielectric loss, mechanical strength, and roughness. A self-constrained laminate is introduced in this article. It consists of inner tapes sintering at especially low-temperature range between 6501C and 7201C and outer tapes with an as-fired surface suitable for thin-film processes.

Fine structuration of low-temperature co-fired ceramic (LTCC) microreactors

“…As compared to the DP951 samples that exhibit more monolithic bonding, the HL2K ones showed a kind of layered structure that was mainly due to the tape's sandwiched structure. 31 It has been evidenced by Jurków 23 that high porosity is obtained in such a layered structure of fired HL2K samples. This might result from HL2K's self-constrained sintering behavior and/or the incomplete burn out of organics.…”

“…The generally poor acid resistance of HL2K agreed with the results in other studies. 31 They seem to exhibit less severe degradation in H 2 SO 4 than in HCl. HL2K is rich in calcium and lanthanum oxides, such as CaAl 2 B 2 O 7 and LaBO 3 , and is not supposed to be very acid-resistant.…”

“…Moreover, the tape structure of HL2K is believed to be another explanation for its weak acidic resistance. As Rabe et al 31 indicated, HL2K is a composite of three layers of ceramic thin tapes sandwiched together, with outer porous layers rich in glassy phase. These outer layers can easily be reacted with aggressive chemicals, resulting in fast dissolution especially in HCl, compared with DP951 that has a more homogenous structure of mixed glass and refractory materials.…”

“…Upon firing, these layers constrain mutually resulting in HL2K having a nearly zero fired planar shrinkage. 31 For the material stability evalua- The concentrated sodium hydroxide solution was additionally used to investigate the leaching stability of the LTCC materials, as the silicate-based glass content of LTCC is very soluble in this condition. 13 The weight loss of LTCC and alumina samples, stored at room temperature, was measured after 1, 2 and 4 weeks.…”

The Effects of Sintering Temperature Variations on Microstructure Changes of LTCC Substrate

“…It is not an easy task because all process parameters (lamination, binder burnout, sintering) and material properties (high temperature reactivity, thermal expansion, etc.) must be matched (Rabe et al, 2005). Furthermore, the material quality of the finished product and process conditions also must be optimized in micro and macro structures in order to make sure work in progress are homogeneous at each process step (Imanaka, 2005).…”