Patent ID: 7788948

Claim:
A process for producing a substrate comprising: heat treating a powder of borosilicate glass, pulverizing the heat treated powder of borosilicate glass, placing the pulverized heat treated powder of borosilicate glass in an atmosphere with a relative humidity of at least 55% at a temperature of at least 30° C. to remove boron, and firing a green sheet comprising the pulverized, heat treated and boron removed powder of borosilicate glass to form the substrate, wherein the heat treating of the powder of borosilicate glass consists of holding the powder of borosilicate glass at a temperature for at least 3 hours at atmospheric pressure, the temperature being higher by at least 30° C. than the glass transition temperature of the powder of borosilicate glass and lower by at most 50° C. than the softening point of the powder of borosilicate glass, and wherein, after the powder of borosilicate glass is formed, but prior to the heat treating of the powder of borosilicate glass, the powder of borosilicate glass is not previously heat treated.