reactance of 0805 and smaller SMT resistors? preferred suppliers?

John Nieznanski (jniez@kodak.com)
Thu, 12 Jun 1997 13:34:17 -0400

Hello SI-list readers/contributors:

>From Motorola's "MECL SYSTEM DESIGN HANDBOOK", 4th ed. ,1988, p.66-67,

"Standard carbon resistors were carefully measured at high frequencies
to determine their reactive components. Results are listed in Fig. 4-4

Fig. 4-4 Impedance Characteristics of Carbon
Resistors Measured on a GR Admittance Bridge

Test Condition Z = R + jX
============== ==========

1/2W, 51 ohms, 500 MHz Z = 51.8 + j15.5
1/2W, 51 ohms, 300 MHz Z = 51.4 + j5.6
1/4W, 51 ohms, 500 MHz Z = 48.8 + j6.1
1/4W, 51 ohms, 300 MHz Z = 49.4 + j0.29
1/8W, 51 ohms, 500 MHz Z = 51.5 + j6.7
1/8W, 51 ohms, 300 MHz Z = 51.7 + j1.6

The effective circuit is a resistor with an inductor in series. Carbon
resistors display more inductive reactance as the resistor values become
smaller, and display more capacitive reactance as the values get larger.
However, 75 ohm resistors are normally close to being purely resistive."

I have several questions:

1. Has any work been published on the high frequency behavior of
physically small SMT resistors (0805 and smaller) on PWBs? I am
interested in obtaining characterization data for a range of resistance
values (from 0 ohm resistors [shorts] up to about 1 kilohm) over as
broad a frequency range as possible, hopefully up to a few (<10) GHz.

2. What suppliers have provided the most consistent, low reactance SMT
resistors?

3. What parameters (resistance values, physical dimensions, thin film
formulations, base material composition, terminator metallizations,
special processing, operating temperature range, etc.) must be
controlled to ensure compliance with these objectives?

4. Has anybody investigated how SMT assembly/rework processes affect
these high frequency characteristics?

Thanks in advance for any inputs you may be able to provide to this
worthwhile cause!

-- 

============================================================ John Nieznanski Eastman Kodak Co. jniez@kodak.com 2/4/EP MC35313 PH: 716-726-2520 901 Elmgrove Rd. FX: 716-726-0745 Rochester, NY 14653-5313 ============================================================