Process for producing ceramic substrate

A method for producing a ceramic substrate comprising the steps of:

• producing an unfired composite laminate comprising an unfired base material layer including a low-temperature sintering ceramic material as a main component and a shrinkage suppression layer including a hard sinterable ceramic powder as a main component, the hard sinterable ceramic powder not being substantially sintered at a sintering temperature of the low-temperature sintering ceramic material, the shrinkage suppression layer being provided on at least one principal surface of the base material layer;
• firing the unfired composite laminate at the sintering temperature of the low-temperature sintering ceramic material, thereby providing a ceramic substrate of the sintered base material layer;
• and
• removing the shrinkage suppression layer to extract the ceramic substrate;
• wherein
• in the step of producing the unfired composite laminate, a solid open bore forming material is added in the shrinkage suppression layer, the solid open bore forming material disappears in the step of firing to form open bores in the shrinkage suppression layer, the solid open bore forming material being uniformly or substantially uniformly dispersed at least in the principal surface direction of the shrinkage suppression layer;
• and
• none of the open bores extends entirely through the shrinkage suppression layer.