Circuit fabrication using a particle filled adhesive

Details Circuit fabrication using a particle filled adhesive Circuit fabrication using a particle filled adhesive

1999-03-12

2001-03-27

Lee, Eddie C. (Department: 2815)

Active solid-state devices (e.g., transistors, solid-state diode

Combined with electrical contact or lead

Of specified material other than unalloyed aluminum

C257S759000, C257S789000

Reexamination Certificate

active

06208031

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to circuit fabrication. More particularly, the invention involves the use of a particle filled adhesive coating in circuit fabrication.
Printed circuit boards (PCBs) typically are used as a replacement for wiring to connect electrical components of an intricate electrical system. PCBs save space, weight and labor, and increase reliability of the circuit as compared with round wire connections. Instead of metal round wire, the conventional PCB includes a metal foil layer (e.g., a copper foil layer) which is adhered to a base (e.g., a fiberglass/epoxy board). Once adhered to the base, the foil layer is then imaged and etched into a desired pattern of conductive lines to form a circuit. Foil layers may be adhered to both sides of the base to produce a double-sided circuit.
A particular type of printed circuitry, often called flexible circuits, or “flex,” has the same basic structure as conventional hard PCBs, or “hardboards.” Flexible printed circuits typically offer many advantages over standard hardboard printed circuits and round wire technology. For example, due to its flexibility, connection of a flexible circuit to a read/write head of a hard disk drive permits cycling of the head across the disk drive many millions of times.
The flexible printed circuit is formed from at least one conductive foil layer (e.g., a copper foil layer) that is adhered to a flexible base film. This base film typically is an electrically nonconductive, or dielectric, film substrate, such as polyimide film or a polyester film (e.g., PEN film or PET film). Similar to the PCB, once adhered to the base film, the foil typically is then imaged and etched into a desired pattern to form a circuit. The foil may be adhered to both sides of the base film to produce a double-sided flexible circuit. Adhesives (e.g., polyimides, epoxies and acrylics) may be used to bond the foil layer to the film substrate. However, the foil layer may also be adhered to the film substrate without adhesives by using, for example, plating or vapor deposition.
Although the base film provides surfaces for a double-sided circuit, many complex circuit designs require more than two layers for electrical connection requirements. Therefore, quite often the flexible circuit requires additional copper layers to yield a “multi-layer” circuit. The inner double-sided circuit is often called the core of the flexible circuit.
Referring to
FIG. 1
, as an example, to form a multi-layer circuit
10
, metal foil layers
12
(only one foil layer
12
is shown in
FIG. 1
) are adhered to, or laminated, to both sides of a dielectric film substrate
14
to create an inner core
16
. The foil layers
12
are then imaged and etched to form conductor lines
18
, as shown in
FIG. 2
, (only one conductor line
18
is shown in FIG.
2
). Thus, the inner core
16
provides up to two etched foil layers of conductor lines.
To form additional etched layers, additional outer foil layers
20
may be laminated to inner core
16
on top of the existing etched foil layers (i.e., on top of existing conductor lines
18
). Outer foil layers
20
may then be etched to create additional conductor lines.
Lamination of the foil layers typically includes the use of high temperature and high pressure. As a result, the adhesive that bonds adjacent layers together tends to flow away during lamination. In this manner, conductor lines on different layers may contact each other. To prevent this from occurring, dielectric films
22
are placed between adjacent foil layers.
Thus, multi-layer flexible circuits have traditionally used dielectric films to separate adjacent etched foil layers. As a result, typically, the overall thickness of the flexible circuit is limited by the thickness of these layers.
SUMMARY OF THE INVENTION
The invention is generally directed to using a particle-laden adhesive compound to mount conductive layers of a circuit assembly (e.g., a flexible printed circuit or a printed circuit board (PCB)) together.
In general, in one aspect, a circuit assembly has a substrate layer, a first conductive layer mounted to the substrate layer and a second conductive layer. The circuit assembly also has an adhesive layer mounting the first and second conductive layers together and having particles for separating the first and second conductive layers.
In accordance with one or more embodiments of the invention, the substrate layer may be a flexible substrate of a flexible circuit. The particles may be dielectric particles, thermally conductive materials or ceramic particles. The adhesive layer may also include an adhesive base, and the particles have a concentration in the adhesive layer between two and forty percent. The adhesive layer may be between four and 150 microns thick. The adhesive layer may include a thermoplastic adhesive or a thermoset adhesive. The first conductive layer may have an etched circuit pattern.
In general, in one aspect a method for making a circuit assembly includes mixing particles with an adhesive base to form an adhesive material, using the adhesive material to mount at least two conductive layers of the circuit assembly together and using the material to keep conductive traces of the layers isolated.
In accordance with one or more embodiments of the invention, the mixing particles with an adhesive base may be mixing dielectric particles, thermally conductive particles or ceramic particles with an adhesive base.
In general, in one aspect, a circuit assembly has an inner core, a first conductive layer mounted to the inner core and a second conductive layer. The circuit assembly also has an adhesive layer mounting the first and second conductive layers together having particles for separating the first and second conductive layers. The circuit assembly may include a third conductive layer and another adhesive layer mounting the second and third conductive layers together having particles for separating the second and third conductive layers.
In general, in one aspect a flexible circuit has an inner flexible core, a first foil layer mounted to the inner core and a second foil layer. The flexible circuit also has an adhesive layer mounting the first and second foil layers together having particles for separating the first and second conductive layers.
Other advantages and features will become apparent from the following description, the claims and the attached drawings.


REFERENCES:
patent: 3652907 (1972-03-01), Page et al.
patent: 4118595 (1978-10-01), Pfahnl et al.
patent: 4141055 (1979-02-01), Berry et al.
patent: 5120665 (1992-06-01), Tsukagoshi et al.
patent: 5164816 (1992-11-01), Nishizawa et al.
patent: 5384690 (1995-01-01), Davis
patent: 5688584 (1997-11-01), Casson et al.
patent: 5781412 (1998-07-01), de Sorgo
patent: 5977642 (1999-11-01), Appelt et al.

Affiliated with

Also associated with

Rating

Circuit fabrication using a particle filled adhesive does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Circuit fabrication using a particle filled adhesive, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit fabrication using a particle filled adhesive will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2485943