Browse Prior Art Database

TRIMMABLE CAPACITOR WITH LASER OR MANUALLY OPENABLE SHORT FOR FILTER TRIMMING

IP.com Disclosure Number: IPCOM000006516D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-11
Document File: 2 page(s) / 92K

Publishing Venue

Motorola

Related People

Robert L. Sapashe Jr.: AUTHOR [+2]

Abstract

Due to unavoidable component tolerances, prese- lectors and other discrete, L-C falters often need to be tuned. In our factories, this is most easily accomplished by laser trimming, using Dishal's method (Dishal, M. "Alignment and Adjustment of Synchronously Tuned Multiple-Resonant-Circuit Filters:' Electrical Commu- nication, pp. 154-164, June 1952). In this method, each filter pole is tuned individually, with the untuned poles severely detuned or, in practice, shorted. As the tuning proceeds, shorted poles are unshotted one at a time, then tuned. While extremely accurate and repeatable, this trimming method does require that each filter pole be manufactured in a shorted condition, then unshorted during the trimming process. At present, this is accom- plished by separate O-ohm resistors, placed in each falter pole and opened by laser as required. After the tuning procedure is complete, the now-open resistors are left on the circuit board for the lie of the product, serving no function.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Page 1 of 2

MOTOROLA INC. Technical Developments Volume 16 August 1992

TRIMMABLE CAPACITOR WITH LASER OR MANUALLY OPENABLE SHORT FOR FILTER TRIMMING

by Robert L. Sapashe Jr. and Edgar H. Callaway, Jr.

  Due to unavoidable component tolerances, prese- lectors and other discrete, L-C falters often need to be tuned. In our factories, this is most easily accomplished by laser trimming, using Dishal's method (Dishal, M. "Alignment and Adjustment of Synchronously Tuned Multiple-Resonant-Circuit Filters:' Electrical Commu- nication, pp. 154-164, June 1952). In this method, each filter pole is tuned individually, with the untuned poles severely detuned or, in practice, shorted. As the tuning proceeds, shorted poles are unshotted one at a time, then tuned. While extremely accurate and repeatable, this trimming method does require that each filter pole be manufactured in a shorted condition, then unshorted during the trimming process. At present, this is accom- plished by separate O-ohm resistors, placed in each falter pole and opened by laser as required. After the tuning procedure is complete, the now-open resistors are left on the circuit board for the lie of the product, serving

no function.

  This invention will eliminate a O-ohm chip resistor for each preselector falter pole now trimmed in the fac- tory with Dishal's method This wilJ simplify board layout, reduce board space, parts count, direct material cost, and defects accordingly. Trimming time will also be reduced, since the laser will have fewer components to target.

  The invention springs from the realization that many tunable capacitors, manual or laser, are used in filters trimmed by Dishal's method. That is, it would be to great practical advantage if the capacitor were to be ini- tially a short circuit, as described above. Consider fast the case of the laser trimmable capacitor. The design of commerciaJJy available laser trimmable capacitors is gen- erally of one of two types (seen in cross section):

i Dielectric 1

Solder pad

Type 2

Dielectric

Sold...