Development of Printed Circuit Board Systems through Improved Resin
Matrix Characterization
Marty Choate, Principal Scientist
Kathy Kelly, Principal Engineer
Isola Laminate Systems Corporation
La Crosse, Wisconsin
Abstract:
Printed Circuit Board laminates in various OEM applications are requiring increasingly advanced
laminate material systems with improved thermal, mechanical and dielectric properties. One of the
key components driving the performance of the laminate material as a system is the resin matrix
between the reinforcement substrate. This paper focuses on a development approach to better
measure, resolve, understand and predict the contributions of the resin system matrix in multilayer
printed circuit boards (PCBs) for high speed digital / RF / microwave and other laminate system
applications.
The objective of this paper is to communicate an approach to better characterize resin matrices
and their property interactions with various reinforcement substrates. The primary focus will be on
the thought process and techniques for characterizing and developing resin systems to better
resolve and predict property differences in reinforced composite property behaviour and new OEM
printed circuit board applications.
Introduction:
The process of developing new laminate systems for an increasingly sophisticated PCB market is
becoming more complex and somewhat expensive by traditional development methods as trends
toward thinner constructions, tighter design specifications, high thermal performance and high
frequency applications. The formulator is tasked with balancing an increasing number of
performance factors and must develop better ways to understand components and interactions
comprising any given high performance laminate
The development of laminate systems at the laminator level has historically focused primarily on
prepreg and laminate properties alone with little to no emphasis placed on the quantifiable
contribution of intrinsic cured resin matrix properties. This practice has been mostly justifiable and
often economical for the laminator in the case of most FR4 multilayer and rigid board applications.
The older development method of focusing primarily on downstream process steps begins to want
both economically and practically as the circuit substrate industry is forced to consider an ever
increasing number of new (and often times, initially costly) resin systems and reinforcement
substrates. This need has been driven to meet new OEM design requirements with thinner
constructions and finer lines and spaces with improved thermal and electrical properties.
Development of more technically sophisticated laminate systems requires an improved
understanding of all components of the laminate system, particularly the resin system.
Past studies of both thermoset and thermoplastic resin systems towards the development of nonPCB composite applications in aerospace and defense is legion. This paper will limit its scope to
an overview of the casting process and example relationships found between resin and laminate
properties. This added method of focusing one step upstream of the traditional prepreg and
laminate steps will also attempt to show the economical, time saving and improved resolution
advantages in down selecting resin systems toward the development of new laminate systems.
Overview Process Diagram of Electronic Substrate Development
Figure 1
General Product Development Process
Raw Material Suppliers & Equipment
Design & Redesign
Marketing Consumer Research
Receipt, Test
of Raw Materials
Copper
Resin
Distribution
Customer
Production
Assembly
Customer
Inspection
Glass
Receipt & Test
of Raw Materials
Treaters
Press
Continual Measurement of Processes,
machines., methods, costs
Receipt & Test
of Raw Materials
Production
Production
Assembly
Assembly
Inspection
Inspection
Field Representative
Distributor
2
Process Diagram of Electronic Substrate Resin System Development
Figure 2
RESIN SYSTEM CASTING PROCESS & SCREENING
Compound Resin
Measure :Kinetics- Rheology - Spectroscopy
~1– 2 DAYS Dry per conditions < onset SC temperature > Solvent BP
~1-2 DAYS
~1/2 DAY
Drive off excess solvent to < 1.0%
Pulverize and screen dried friable resin @ 23C or below
~1-2 DAYS Re-evaluate Rheology - Kinetics - Spectroscopy
~1-3 DAYS
Cast resin
1-2 weeks Depending on
TestsTesting
Submit Castings 2for Testing:
Test Electrical, Mechanical , Thermomechanical, Spectroscopic &
Phase Morphology
RECORD & GRAPH ALL DATA
UNDER H:TECH/LOW
The above diagram illustrates a typical cast neat resin screening process to capture many
common thermal, mechanical and electrical properties encountered for PCB.
There are many other tests that could be added or subtracted depending on the question being
asked. The key point is that the resolution achieved when trying to understand the contributions of
the resin and the measurement system can be improved through study of the neat resin as a
discreet system prior to characterizing the complete laminate system. An example of he
magnitude of this resolution difference can be seen in figures 6 & 7.
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Low Loss Resin Laminate Development Process Overview
Resin Varnish-Laminate Development Process
1-5 yrs Trial & Error to Market:
Estimate Laminate Solution
Formulate or Obtain Resin Supplier Resin System
Resin Varnish-Casting-Laminate
Development Process:
6 months - 1yr. To Market
Literature Search
MSE
Intrinsic Resin
Property Knowledge Base
Prepreg Trial Lab Hand Sheets
5-10 yds2 glass/2-6 litres varnish
3-4 systems down-selected
Neat Resin System Screening
Evaluation & Selection system
1-6 litres varnish
Planned Experiment Prepreg
by Lab Hand Sheet system
5-10 yards of glass
Prepreg Trial & Error Treater Runs
100 - 500 yds2 & 1000
5000 litres of varnish ea.
Customer Evaluation
Downselected
Intermediate
Df Laminate
System
Development
1-2 Treater Runs
100 - 500 yds2 &
1000 - 5000 litres
varnish each
Production Laminate
Development
figure 3
Knowledge of neat resins can be measured, saved and applied towards new applications,
decreasing their time to development as knowledge increases. The process is illustrated in figures
3.
4
Product Knowledge Material Consumption
Laminate/PCB
Development
Method Comparison
Method 1:
Trial & Error
Resin/Prepreg/Laminate
T&E Experimentation
to Laminate Scale-Up
Method 2:
Resin Plaque
Characterization
& Development
to Laminate Scale-Up
Time to Development & Material Cost
figure 4
A great deal of time and material can be saved over the course of laminate and PCB development
through the study of fully cured intrinsic resin properties. The two methods are illustrated in figure
4. Method One shown in red using the resin varnish-laminate development approach can actually
consume significantly more time and materials over the long term though initially method 1 may
seem to be apparently the fastest way to market. Method Two although apparently slower initially,
can screen many more potential systems economically (less materials consumed) with improved
accuracy and degree of belief through better understanding of cured resin intrinsic properties with
laminate substrate system components. This knowledge can also lead to faster response times to
technical service material/process issues during the course of the product lifetime. This method
can offer improved resolution between the more subtle characteristics of the cured resin from the
substrate rather than relying on the study of complex laminate systems alone.
Casting Process Development
The manufacture of castings is not an easy proposition with many thermoset resin systems and at
times can seem almost impossible due to varying kinetics, solubility and rheology of different
systems. There are no specific methods for the manufacture of castings in general and the
method for each system must be developed empirically. The characterization of neat resin
systems in prepolymer or monomeric mixtures can serve as guides towards the development of
casting conditions. These tools might typically include DSC for kinetics, Rheometrics (steady state
nondestructive shear) for rheology, various spectroscopic methods and simple bench solubility
determinations. There are various general methods and variations for the manufacture of fully
cured thermoset resin castings that lead beyond the scope of this paper. An example method of
resin casting preparation found useful for many FR4 PCB systems is listed below in Diagram 1.
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Diagram 1
Vacuum Oven Strip Solvent
Neat Resin Casting
Cold pressedpreform
Remove Meringue from Pan
Preform
Match Metal
Compression Mold
40 mesh screen
Resin must thoroughly
melt prior to
applying
pressure.
This method may also be used for the manufacture and study of reinforced cured composites to
study:
a) Improved thickness characterization of small lab samples to better control resin content,
conduct shrink measurements and reducing taper for critical measurements than
conventional PCB press conditions.
b) Studying interfacial adhesion properties between resin, copper and other substrate composite
systems.
c) Achieving specific desired cast surface textures through mold surface finish or interface with
various non-porous substrates.
Examples of some typical castings are shown in figure 5.
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figure 5
As figure 5 illustrates, cured neat resin castings come in many degrees of color and transparency.
These properties can be measured with refractive index and/or various colorimeters for the
purpose of determining cure, resin system properties. These may be useful towards simple
improved laminate color prediction, resin system component compatibility and even microscopic
morphology of phase size separation. Most thermal and mechanical properties related to PCB
performance and manufacture can be measured using many common ASTM & IPC test methods.
Overall improved intrinsic property resolution including interactions between properties can be
achieved with castings using commonly measured laminate property methods.
The application of studying fully cured thermoset resin castings allows for improved resin system
down-selection and performance prediction in reinforced cured composite laminate/PCB systems.
The study of intrinsic resin system properties provides increased resolution between and within
resin system variation that might normally be lost or confounded with process and/or substrate
factors that also profoundly affect cured laminate system properties. Effects of lot to lot resin
system variation can be better resolved in castings and resolve problem approach from a resin,
laminate and/or process viewpoint. Molded cure variation from initial cure conditions of both
castings and laminate systems can be minimized through post cure at or slightly above the cure
temperature (as determined by DSC) when maximum cured system properties are of interest.
Increased quantitative understanding of the interactions of neat resin system components and
true resin cure conditions can be evaluated with a higher degree of belief through the subtraction
of substrate influence. Conversely the effects of substrate on the laminate system can be better
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understood if the intrinsic properties of the cured resin system are known. Resin/glass ratio effects
can realize improved resolution and more accurate predictive models developed. An example of
the magnitude difference in determining property interactions between DSC Tg and moisture
absorption as well as the effects of different glass influence can be seen in figures 6 & 7.
figure 6.
DSC Tg & % Water Gain 24/100 Comparing Resin Systems A & B vs. Respective 8 ply 7628
Laminate Constructions using Resins A & B
Tg DSC
24/100 % moisture
190
2.5
2.36
184
185
2
180
179
177
1.5
% by wt.
Deg C
175
170
1.088
164
165
0.989
1
0.778
160
0.5
155
150
0
FR4 Resin A
FR4 Laminate 8 ply 7628
43% Resin A
FR4 Resin B
FR4 Laminate 7628 43%
Resin B
Sample Description
figure 7.
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Resin C & D Castings vs. C & D Resin on 6 ply 1080 vs. 8 ply 7628 Constructions
TMA Tg
cte 23 - 150 C
220
70
65
210
60
55
200
190
45
ppm
deg C
50
40
180
35
170
CASTING DATA
C vs. D RESIN SYSTEMS
30
1080 LAMINATE DATA
C vs. D RESINS
7628 LAMINATE DATA
C vs. D RESINS
160
25
20
FR4 Resin C
FR4 Resin D
FR4 Laminate FR4 Laminate
1080 68%
1080 68%
Resin C
Resin D
FR4 Laminate FR4 Laminate
7628 43%
7628 43%
Resin C
Resin D
While there are apparent significant differences in the magnitude of DSC and absorption property
interactions between FR4 resin systems A & B in figure 6. These differences are somewhat
obscured in figure 7 when comparing resin systems A & B on 1080 68% RC and 7628 43% RC
woven glass systems using common sizing agents. The confounding factors are primarily resinglass ratio, weave style and layer count that somewhat dampen the relationship between the two
resin systems. These differences and/or similarities can be constructively applied, depending on
the question being asked, in models useful towards improved prediction of a given resin system in
various laminate systems and constructions.
Summary of Advantages using Neat Resin Characterization Development
Method:
1.
2.
3.
Reduce development time and cost by lowering initial resin and glass material consumption
when laminate system knowledge is low, particularly where newly synthesized or limited
availability resins and/or additives are being evaluated.
Improved resin system property resolution to better down select discreet differences from
what might otherwise be confounded with intrinsic laminate properties. (resin/glass ratio,
weave styles, prepreg process, layer counts….)
Enhance the ability to resolve property differences in color, specific gravity, thermal
conductivity, toughness and other subtle resin properties that may become increasingly
important as laminates decrease in thickness and PCB designs become increasingly
demanding.
References:
1. Stephen J. Mumby, “ An Overview of Laminate Materials with Enhanced Dielectric
Properties.” J. Electron. Mateer., Vol. 18 (2), P. 241-250 (1989).
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2. T.D. Newton, “ Predicting Dielectric Properties.” Proc. Of the IPC Mg. In Boston, Spring 1986.
3. Fundamental and Industrial Applications of MW & RF Fields by G. Roussy and J.A. Pearce.
4. A. B. Bereskin, “ Microwave Dielectric Property Measurements.” Microwave Journal, vol 35,
no.7, pp. 98 – 112.
5. D.R. Moore et al - Testing for Toughness and the Development of Toughened Thermosetting
Moulding Compounds SAE International Congress and Exposition 1990, Detroit MI 890251
6. M. Choate, P. Eustace - Toughened Epoxy Resin Molding Compounds RETEC, 1990,
IL.
Chicago
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