Multilayer is quickly
becoming the standard. Low layer count products represent
the largest proportion of these types with 4 layer boards
outnumbering almost all other layer counts combined.
Eddy Electronics can
produce up to 12 layer printed circuits with what is in stock at
all times.
Multilayer boards are
made by etching thin double sided panels ( cores ) and laminating
them together with uncured fibre-glass sheets ( prepreg ).
Alignment is accomplished with a series of tooling holes and
pins. When the laminated panel is drilled and plated
through, the vertical connections are made.
Blind or buried vias
are inner connections made when the cores are plated through prior
to lamination. This allows multiple connections to be made
at a single X-Y coordinate, the vias being isolated in the Z
(vertical) direction.
Internal ground and
power planes are useful for efficient distribution of power and
the elimination of noise. Ground loops on audio or RF
products can be rendered impossible. Digital and analog
signals can isolated completely with little effort.
Impedance can be controlled in critical areas to improve high
speed, high power or low noise applications. The coolest
application of internal metal is as heat sink. The space
program could probably not exist with out it! Power density
of a printed circuit product can be increased
enormously.
Obviously, this
technology allows vast flexiblity to the designer, and coupled
with options in substrate type and copper thickness, a great deal
of product capability can made on a single circuit
board.
Check with us or ask specific questions before you
get commited to a design. There are things you need to
know!
This is a shot that
illustrates a useful design for manufacturability (dfm)
tool. The window in the centre has 8 panes, one for each
layer in this 8 layer backplane. One can tell that each
piece of film has its number assigned in a way that prevents any
confusion. The final product is verifiable in the sense that
one can tell how the layers were laminated. The order of
lamination has to be specified so that the desired effects of
multilayer construction are achieved.
You can also see internal tracks
running under the surface near the bottom and top of this
board.
