BACKGROUND
IN 1992, CEDAL EQUIPMENT STARTED DEVELOPMENT OF THE
ADARA SYSTEM. THE REVOLUTIONARY
CONCEPT WAS TO HEAT A STACK OF MULTILAYERS OR BASE LAMINATE MATERIALS, BY PASSING
ELECTRIC CURRENT THROUGH A CONTINUOUS BAND OF COPPER.
THE ADVANTAGES WERE READILY APPARENT. USING THIS METHOD OF HEATING, THE COPPER IS THE HEATER AND IS IN INTIMATE
CONTACT WITH THE MATERIALS TO BE RESULTING IN UNIFORM TEMPERATURE WITHIN THE WHOLE STACK.
THE
ADARA SYSTEM IS ALREADY PRESENT IN MANY PCB FACTORIES WORLDWIDE.
BASE MATERIALS AND MULTILAYERS MADE WITH
ADARA PRESS MEET THE EXPECTATION FOR HIGHER QUALITY.
THE GOOD ENGINEERING LEVEL OF THIS MACHINE AND ITS HIGH PRODUCTIVITY MADE THE
ADARA SYSTEM FOCUSED FOR IMPROVING
THE PCB FABRICATION.
COMPARISON WITH TRADITIONAL PRESS SYSTEM
IN A TRADITIONAL PRESS THE MATERIALS ARE LAID UP BY USING SHEETS OF COPPER FOIL ALONG WITH THE
INNERLAYER AND PREPREG OR, IN CASE OF LAMINATE, ONLY PREPREG. A STAINLESS STEEL PLATE
USUALLY SEPARATES EACH PIECE. THE SMALL STACKS OF ABOUT 30 mm HEIGHT ARE THEN PLACED INTO THE SEVERAL
OPENINGS OF THE PRESS AND HEATED BY THE PLATEN ABOVE AND UNDER THE STACKS; IT IS NECESSARY TO
HEAT AT A SLOW RATE TO AVOID OVERHEATING THE OUTER PROCESS. EVEN WITH SLOW HEATING THERE WILL BE
TYPICALLY 30°C DIFFERENCE BETWEEN THE OUTER PIECES AND THE CENTRE PIECES.
AT A CERTAIN TEMPERATURE, DEPENDING ON THE NATURE OF THE PREPREGS, THE EXPOSY WILL BECOME LIQUID
AND THEN AT A HIGHER TEMPERATURE WILL BECOME SOLID AGAIN AS THE RESIN POLYMERIZES (CURES).
WITH SUCH A LARGE DIFFERENCE IN TEMPERATURE SOME OF THE MATERIALS WILL BE SOLID AND SOME WILL BE LIQUID.
THERE IS NO GREAT CONSEQUENCE IF THE TEMPERATURE DIFFERENCE IS ONLY IN THE Z -AXIS, BUT IF THERE IS A
DIFFERENCE IN THE XY PLANE, THE THERMAL STRESS PRODUCES A DISTORTION
OF THE MATERIALS.
WITH THE
ADARA, THE MAXIMUM DIFFERENCE BETWEEN ANY TWO POINTS IN THE STACK
WILL BE NO MORE THAN 5 °C IN THE Z-AXIS. IN THE X-Y AXIS THERE IS BASICALLY NO DIFFERENCE.
THE MOST INNOVATIVE POINTS OF ADARA PRESS
HEATING SYSTEM
In the traditional presses, the plates heating system are made by electrical heaters or by flow
of oil or other liquid which are separately heated.
Since the heat exchange between the hot plates and the material to be pressed is made by
simple contact,it is understandable that not many sheets of it can be applied
simultaneously between the two plates.
The resin material, in fact, is a bad heat conductor, so the material sheets can have up to 30°C
of temperature difference in the various sheets levels.
This temperature gap reduces when the material reaches the final polymerization temperature.
In the
Adara press the material is heated by the Joule effect directly in the copper foils
which envelop the resin sheets. Each material sheet is heated then, by the copper foil which is in
intimate contact with it and plays as a heater.
By this system the temperature gap between two multilayers is not over ±3°C.
That means a great quality value even if the pre-preg has not constant performances.
Due to the controllable heating system in real time by electrical parameters, in the
Adara press there is
not needs to use any Kraft or other tools to slow down the heating effect as per the traditional presses.
In the
Adara Press it is very easy to control the flow during pressing cycle by working
on the internal stack temperature and its rising rate.
A rise of 2°C/min. reduces the flow effect, while a rise of 4°C/min. generates a good flow effect.
By controlling all these process parameters it is possible to minimize voids in the circuits.
Many
Adara users have reduced the free spaces around the PCB, at less than 15
mm
on the multilayers with more than 4 layers, also at about 10
mm on multilayers with 4 layers.
The minimum flow allows to reduce the over dimension of prepregs from 50
mm
which is in standard press, to 30
mm with
Adara press