Subject:                              Time:  9:02 AM
  OFFICE MEMO         FAB: E-GLASS VS. S-GLASS              Date:  3/1/96

Jim Marsico, [log in to unmask], queried about the differences between E-glass
and S-glass fabrics as follows:

"Can anyone describe the differences in physical properties between E-glass
and S-glass cloth?  What resin is typically used with S-glass?"

Reply -- 

In general, S-glass and D-glass fabrics are used with higher performance resin
systems for sophisticated printed boards, mostly multilayers.

The following are some of the properties:

                                        Glass type
                           |    "E"    |      "S"    |     "D"     |
Tensile, lb/sqin  |  500 k  |  600+ k  |  300+ k  |
TCE ppm/deg F    |    2.8    |     1.6     |     1.7     |
Dk @ 10 M#005##005##005##005#Hz        |  ~6.1    |   ~5.2    |      ~4  
  |
Df @ 10 MHz        | ~0.004 | ~0.007   | ~0.003  |

The drivers for the use of "S" and "D" are the electricals Dk and thermal TCE.
 With lower Dk's propagation velocity is increased and capacitance is reduced.
 Thermally, the alternative glasses encourage the reliable direct surface
mounting  of large ceramic components on the printed board's surface(s) that
are subjected to thermal cycling and shock, and power cycling; without the use
of constraining cores.  Most "S" and "D" glass printed boards are used in
digital systems where the Df is generally not a major concern due to the
"drive" capability of digital circuitry.  

The resin systems are generally the "higher performance" generally the cyanate
esters, sometimes polyimide, sometimes tetra/poly functional epoxies, and
seldom di-functional epoxies.

Ralph Hersey
Lawrence Livermore National Laboratory
Phn:  510.422.7430
FAX:  510.424.6886
e-mail:  [log in to unmask]