Circuit boards including capacitive coupling for signal transmission and methods of use and manufacture

• US 5,466,892 A
• Filed: 02/03/1993
• Issued: 11/14/1995
• Est. Priority Date: 02/03/1993
• Status: Expired due to Term

• Current Assignee: Hadco Santa Clara Incorporated (Sanmina-SCI Corporation)
• Original Assignee: Zycon Corp. (Sanmina-SCI Corporation)
• Inventors: Howard, James R., Lucas, Gregory L.
• Primary Examiner(s): Thomas, Laura
• Application Number:
  US08/013,076
• Time in Patent Office: 1,014 Days
• Field of Search: 174/261, 174/255, 174/250, 361/790, 361/795, 361/748
• US Class Current: 174/261
• CPC Class Codes: H05K 1/0239 Signal transmission by AC coupling
• CPC Class Codes: H05K 1/0298 Multilayer circuits
• CPC Class Codes: H05K 1/112 directly combined with via connections
• CPC Class Codes: H05K 1/162 incorporating printed capacitors
• CPC Class Codes: H05K 2201/09672 Superposed layout, i.e. in different planes
• CPC Class Codes: H05K 2201/10689 Leaded Integrated Circuit [IC] package, e.g. dual-in-line [DIL]

Abstract

A circuit board and method of forming a circuit board with signal and receptor pads arranged on layers spaced apart in a Z direction with a dielectric layer therebetween, parameters of a resulting AC signal transmitting circuit resulting wherein:

capacitive reactance is defined by the equation (I) ##EQU1## where F is frequency and C is capacitance; inductive reactance is defined by the equation (II)

X.sub.L =2πFL

where F is frequency and L is inductance;

capacitance is defined by the equation (III) ##EQU2## where A is the effective mutual area of the signal and receptor pads, D is Faraday'"'"'s constant, E is the dielectric constant, and τ is the thickness of the dielectric layer; and

inductance is defined by the equation (IV)

L=0.005 ln (4h/d)μH/in.

where ln indicates the natural logarithm for the value 4h/d, where h is the distance above a ground plane, and d is the equivalent diameter of a conductor;

wherein capacitance and inductance are established in equations I and II with X_C and X_L being equal or approaching equality and the values of A, D, τ, I_N, h (etc.) are preselected or calculated from equations III and IV.

Claims

1. A circuit board for mounting electrical components and having conductive layers spaced apart and electrically insulated from each other, and at least one circuit for transmitting AC signals from one layer to another, the AC signal transmitting circuit comprising

a conductive signal pad formed by a first conductive layer in the circuit board and adapted for coupling with means for generating an AC signal,

a conductive receptor pad formed by a second conductive layer in the circuit board and adapted for coupling with means for responding to the AC signal, and

a dielectric layer arranged between the signal and receptor pads, the thickness and dielectric constant of the dielectric layer and the respective areas of the signal and receptor pads being selected for developing effective capacitive coupling between the signal and receptor pads in order to electrostatically transmit the AC signal from the signal pad to the receptor pad,

the signal and receptor pads and the dielectric layer having electrical characteristics approaching a resonant frequency condition in the AC signal transmitting circuit whereby capacitive reactance and inductive reactance approach equality in order to optimize capacitive coupling.

2. The circuit board of claim 1 further comprising additional conductive circuit means formed on the first and second conductive layers, the thickness and dielectric constant of the dielectric layer, the respective areas of the signal and receptor pads also being selected in combination with spacing of the additional conductive circuit means front the signal and receptor pads for minimizing capacitive coupling with the additional conductive circuit means.

3. The circuit board of claim 2 wherein the additional conductive circuit means on the first and second conductive layers form additional signal and receptor pads separated by additional dielectric layers for developing effective capacitive coupling between sets of the additional signal and receptor pads on the first and second conductive layers also for electrostatic transmission of AC signals therebetween.

4. The circuit board of claim 1 wherein the circuit board is of a multi-layer type having at least a third conductive layer and further wherein the additional conductive circuit means on the adjacent pairs of the first, second and third conductive layers form additional signal and receptor pads separated by additional dielectric layers for developing effective capacitive coupling between sets of the additional signal and receptor pads on the first and second conductive layers for electrostatic transmission of AC signals therebetween.

5. The circuit board of claim 1 wherein:

capacitive reactance is defined by the equation (I) ##EQU6## where F is frequency and C is capacitance;

inductive reactance is defined by the equation (II)

space="preserve" listing-type="equation">X.sub.L =2π

FL

where F is frequency and L is inductance;

capacitance is defined by the equation (III) ##EQU7## where A is the effective mutual area of the transmitting and receptor pads, D is Faraday'"'"'s constant, E is the dielectric constant, and τ

is the thickness of the dielectric layer; and

inductance is defined by the equation (IV)

space="preserve" listing-type="equation">L=0.005 ln (4h/d)μ

H/in.

where ln indicates the natural logarithm for the value 4h/d, where h is the distance above a ground plane, and d is the equivalent diameter of a conductor;

wherein capacitance and inductance are established in equations I and II with X_C and X_L being equal or approaching equality and the values of A, D, τ

, I_N, h (etc.) are preselected or calculated from equations III and IV.

6. The circuit board of claim 5 wherein capacitance is initially selected followed by calculation of capacitive reactance from equation I with inductive reactance being assumed equal to or approaching equality with capacitive reactance.

7. A method of forming a circuit board for mounting electrical components and having conductive layers spaced apart and electrically insulated from each other, and at least one circuit for transmitting AC signals from one layer to another, comprising the steps of forming a conductive signal pad and conductive receptor pad on surfaces of the circuit board spaced apart in a Z direction with a dielectric layer therebetween,

the conductive signal pad being adapted for coupling with means for generating an AC signal,

coupling the conductive signal pad with means for generating an AC signal,

coupling the conductive receptor pad with means for responding to the AC signal,

selecting the thickness and dielectric constant of the dielectric layer and the respective areas of the signal and receptor pads for developing effective capacitive coupling between the signal and receptor pads in order to electrostatically transmit the AC signal from the signal pad to the receptor pad, and

selecting electrical characteristics of the signal and receptor pads and the dielectric layer to approach a resonant frequency condition in the AC signal transmitting circuit whereby capacitive reactance and inductive reactance approach equality in order to optimize capacitive coupling.

8. The method of claim 7 further comprising the step of forming additional conductive circuit means on the first and second conductive layers, the thickness and dielectric constant of the dielectric layer, the respective areas of the signal and receptor pads also being selected in combination with spacing of the additional conductive circuit means from the signal and receptor pads for minimizing capacitive coupling with the additional conductive circuit means.

9. The method of claim 8 wherein the additional conductive circuit means on the first and second conductive layers form additional signal and receptor pads separated by additional dielectric layers for developing effective capacitive coupling between sets of the additional signal and receptor pads on the first and second conductive layers also for electrostatic transmission of AC signals therebetween.

10. The method of claim 7 wherein the circuit board is of a multi-layer type having at least a third conductive layer and further wherein the additional conductive circuit means on the adjacent pairs of the first, second and third conductive layers form additional signal and receptor pads separated by additional dielectric layers for developing effective capacitive coupling between sets of the additional signal and receptor pads on the first and second conductive layers for electrostatic transmission of AC signals therebetween.

11. The method of claim 7 wherein:

capacitive reactance is defined by the equation (I) ##EQU8## where F is frequency and C is capacitance;

inductive reactance is defined by the equation (II)

space="preserve" listing-type="equation">X.sub.L =2π

FL

where F is frequency and L is inductance;

capacitance is defined by the equation (III) ##EQU9## where A is the effective mutual area of the transmitting and receptor pads, D is Faraday'"'"'s constant, E is the dielectric constant, and τ

is the thickness of the dielectric layer; and

inductance is defined by the equation (IV)

space="preserve" listing-type="equation">L=0.005 ln (4h/d)μ

H/in.

where ln indicates the natural logarithm for the value 4h/d, where h is the distance above a ground plane, and d is the equivalent diameter of a conductor;

wherein capacitance and inductance are established in equations I and II with X_C and X_L being equal or approaching equality and the values of A, D, τ

, I_N, h (etc.) are preselected or calculated from equations III and IV.

12. The method of claim 11 further comprising the step of initially selecting capacitance for the AC signal transmitting circuit and then calculating capacitive reactance from equation I with inductive reactance being assumed equal to or approaching equality with capacitive reactance.

13. A circuit board for mounting electrical components and having conductive layers spaced apart and electrically insulated from each other, and at least one circuit for transmitting AC signals from one layer to another, the AC signal transmitting circuit comprising

a conductive signal means formed by a first conductive layer in the circuit board and adapted for coupling with means for generating an AC signal,

a conductive receptor means formed by a second conductive layer spaced apart in a Z direction from the first conductive layer in the circuit board and adapted for coupling with means for responding to the AC signal,

a dielectric layer arranged between the signal and receptor means, characteristics for the conductive signal means, the conductive receptor means and the dielectric layer arranged therebetween being selected for developing effective signal transmission coupling between the signal and receptor means in order to electrostatically transmit the AC signal from the signal means to the receptor means, and

the signal and receptor means and the dielectric layer having electrical characteristics approaching a resonant frequency condition in the AC signal transmitting circuit whereby capacitive reactance and inductive reactance approach equality in order to optimize capacitive coupling.

14. The circuit board of claim 13 wherein the circuit board is of a multi-layer type having at least a third conductive layer and further wherein the additional conductive circuit means on the adjacent pairs of the first, second and third conductive layers form additional signal and receptor means separated by additional dielectric layers for developing effective signal transmitting coupling between sets of the additional signal and receptor means on the first and second conductive layers for electrostatic transmission of AC signals therebetween.