1. Case History: Development of Ink-Jetted Polymer Thick Film Resistors
Situation:
Almost every electronics assembly contains resistors. Some Printed Circuit Boards (PCBs),
especially computer motherboards can contain many hundreds of resistors. There are usually
many different values and sizes of resistors on a PCB. Automated assembly machines called
Pick-and-Place (P&P) machines are used to pick up resistors and other electrical components
from a component holder/feeder and place the component on the proper location of the PCB.
Using discreet resistors requires the purchase and inventory of these parts. P&P machines,
besides being very expensive and occupying a large amount of factory space, require
programming to know where the part feeders are located and where on the PCB surface to place
the resistors. Running automated placement equipment requires trained operators and
maintenance staff. In quantity, resistors cost about one cent each, but the total material, labor
and overhead (MLO) cost associated with using resistors for a large manufacturer is between
four and six cents each.
Prior to this project, there were two alternative methods for obtaining planar resistors on the
outer or inner layers of a PCB. One method is to screen print carbon thick-film resistors on the
outer layer of the board. Polymore Circuit Technologies, LP provides this service, mostly to the
automotive industry. The second method is to use a nickel-phosphorous/copper foil laminated to
one or more inner layers of the PCB during its fabrication. This material, trade named
OhmegaPly by Ohmega Technologies, is photochemical etched in a two-step process to
selectively remove the some of the copper layer and then the underlying nickel-phosphorous
layer to leave nickel-phosphorous resistors on the PCB laminate. Both technologies have
significant limitations, the biggest being that electrical resistance tolerances are limited to
+/- 20% of the desired (designed-in) value. Cost per resistor for both technologies is inversely
proportional to the quantity of resistors per PCB.
Project Conception:
An engineer at Sandia National Laboratories was working with an material composed of
electrically conductive, microscopically small fibrils (fibers). He proposed to The National
Center for Manufacturing Sciences (NCMS) that it was feasible to combine this material with a
liquid polymer, ink-jet dispense it onto a PCB, cure it and create planar electrical resistors.
My role in solution:
I participated in several meetings conducted by NCMS to develop a team to work this effort. I
eventually volunteered to champion it. NCMS assigned a project manager to manage the budget
and maintain the schedule. I was responsible for developing and managing the technical portion
of the project, coordinating the writing of the project report, and authoring the sections detailing
the work led by me at Texas Instruments (TI). At TI, I coordinated the fabrication of the test
boards and coordinated the reliability testing of all test vehicles. Test vehicle fabrication was
done at TI’s Austin, TX PWB fabrication facility. Ink-jetted resistor reliability testing was
performed at TI’s McKinney, TX facility.

2. Project Participants:
• MicroFab, Plano, TX
• Sandia Nation Laboratories, Albuquerque, NM
• Polymore Circuit Technologies, L.P., Maryville, TN
• Delco Electronics, Kokomo, IN (Now Delphi Electronics)
• National Center for Manufacturing Sciences (NCMS), Ann Arbor, MI
• Morton Electronic Materials, Div. of Morton International, Tustin, CA
• Texas Instruments (TI), Defense Systems & Electronics Group, Lewisville, TX
(Now Raytheon Systems Company, Tucson, AZ)
Project Scope:
We decided to divide the effort into three parts or phases, and contractually agreed to work on
Phase 1.
Phase 1 was a feasibility demonstration, requiring:
• Formulation of a material that could be ink-jet dispensed and cured to create resistors
• Development of the ink-jet dispensing and curing technology for the resistor material
• Tighter electrical resistance tolerances than could be achieved by two alternative planar
resistor materials
• Low thermal coefficient of resistance (TCR) over automotive temperatures of –55 o
C to
+ 160 o
C.
• Potential total MLO costs of less than one cent per resistor
If Phase 1 was successful, Phase 2 would be to improve the resistor formulation and to develop
and implement a Beta Ink-jet dispensing machine in a participant’s PCB fabrication facility.
Phase 3 would be full-scale demonstration/implementation of a production resistor dispenser.
Team accomplishment:
The dispensing of the initial materials formulated by Sandia and Morton proved much more
difficult than anticipated, due to the agglomeration of the fibrils prior to curing. Using the
chosen conductive material in a polymer resin required significantly efforts than anticipated at
the inception of the project. These efforts included different materials formulations,
development of a new ink-jet dispensing reservoir technology to maintain homogeneity, and
different curing method trials.
The team finished its efforts in 1999, having completed reliability testing of the ink-jetted
resistors and writing our final report.
Results:
The results demonstrated that ink-jetted resistor technology was capable of surpassing the
original goals for cost and performance. The raw material cost was estimated to be less than
$0.0001 per resistor. The expected savings to users of this technology range from millions to
hundreds of millions of dollars per year, depending on the size of the PCB assembly operations.

3. However, the conductive material selected for use in a polymer resin for this Phase 1 of the
program proved difficult to contain in suspension during formulation, shipping and dispensing.
This required use of a mixing technology that is proprietary to the project team. We
recommended Phase 2 be initiated, and a new conductive ink material be developed.
Phase Two was started in 1999. Project participants include 3M, Delphi, MicroFab, Northern
Telecom (Nortel) and several others. The National Institutes of Science and Technology (NIST),
as an Advanced Technology Program (ATP) is funding the majority of this Phase Two effort.
NCMS is again managing the budgets and maintaining schedules.