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DATA BUS patterning method for PCB of LCD module Disclosure Number: IPCOM000013446D
Original Publication Date: 2000-Oct-01
Included in the Prior Art Database: 2003-Jun-18
Document File: 5 page(s) / 96K

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DATA BUS patterning method for PCB of LCD module


      Disclosed here is a PCB (Printed Circuit Board) patterning method which
is very suitable for PCBs used in LCD (Liquid Crystal Display) module. This
method makes it possible to make the PCB very narrow and also the EMI (Electro
Magnetic Interference) noise from the PCB be better than traditional
patterning methods.

Traditional ways and its disadvantages

      The major LCD module consists of a Liquid Crystal Cell (2 glasses which
sandwich liquid crystal) , Driver-ICs which supplies appropriate voltage to
the LC-Cell, and PCB(s) which provides the data signal to the driver-ICs. To
provide the signals to driver-ICs, via holes are used in PCB to make overhead
crossing of each data line across the data bus.

      The characteristics of the current PCB technology are as follows, so the
PCB patterns made by traditional ways has some disadvantages described later.

Characteristics of current PCB technology and driver-IC :

The minimum line width is 100-150um and the minimum line spacing rule is
The diameter of via holes is about 600um(min) if the via hole is through
hole type. (There exists smaller via hole technology called "laser via"
which is used in build-up PCB technology, however the PCB raw card costs
about 150% compared to ordinary through hole via technology, and in many
case the laser-type via cannot be piled just on top to the other layer
laser-type via, then the space of the via-area may not become small enough
if the data bus is placed in 3rd or more inside of the PCB layers. )

The soldering connection pitch of the input terminals on the driver-IC to
PCB is about 300-400um. (Current TAB soldering or ACF connection)

Traditional way (A) :


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Ca rd width

(Figure 1)

      To minimize the length of the surface pattern from the via to the
driver-IC (called stub line), placing the vias in zigzag position is one of
traditional ways of the patterning methods (Fig. 1) but the data bus meanders
inside the PCB,

That makes the card width to be wide. This may be a disadvantage of making
thinner & lighter LCD modules and may make it difficult to comply with the
SPWG (Standard Panel Working Group : LCD module standardization group and
also its standard) connector position etc.

    That makes the electrical length of the data bus be longer, it may be a
disadvantage from the point of EMI
(In the figure, The blue lines are the surface patterns from via to driver-IC,
the magenta ones are the data bus in internal layer of the PCB.)

Traditional way (B) :


(line : 100-150um /

 space : 100-150um)

Pitch of the driver terminals : 300-400um


(Figure 2)

      To make the PCB width narrower, placing the data bus to be straight as
possible not have to detour the vias, is the other traditional way of
patterning methods but the vias have bigger scale than the pitch of the
driver-IC terminals so,

The area of vias spreads out maybe over to the next driver-IC area, that
makes the surface l...