1. Thermally Conductive Substrates; A Rapidly Growing PCB Mfg Opportunity
Thank you for your kind introduction…
I am Mark Goodwin from Ventec (Leave it at that. Don’t do the big corporate intro!)
There’s increasing interest in cost-effective thermal management of electronics
Thermally conductive printed circuit substrates are becoming the solution of choice
I will try to give an overview of some of the available options and applications, and the main processing characteristics
I will raise a few questions about suitability for purpose, and some reliability considerations.

2. Thermal Management Requirements Increasing in Demand in the Marketplace
Areas of Thermal Substrate Application Development;
Power Electronics: DC power supplies, inverters, power controllers, motor drivers.
Automotive Electronics: ABS braking modules, brake energy regeneration
High Speed Computing: Higher speeds mean more excess heat to dissipate.
LED lighting: Backlit LCD monitors*, commercial displays, municipal lighting.
The need to dissipate heat from electronic modules and assemblies is becoming increasingly important--not only as a consequence of the inevitable "smaller, faster" trend for microelectronics to operate at higher frequencies and higher-performance levels.
In the field of automotive engineering, an increasing number of functions, previously accomplished mechanically, are now solved electronically: Braking and power steering are two examples.
Elsewhere in power electronics, thermal management becomes a critical consideration in the design of DC power supplies, inverters, power controllers and motor drivers.
But it is the exponential growth in LED technologies that is creating huge market demand for efficient, reliable, low-cost thermal management solutions.

3. Everywhere lighting is in use, LED designs will replace it
Thermal Management Requirements Increasing in Demand in the Marketplace
(Almost)
Everywhere lighting is in use,
LED designs will replace it
within 5-8 years.
The need to dissipate heat from electronic modules and assemblies is becoming increasingly important--not only as a consequence of the inevitable "smaller, faster" trend for microelectronics to operate at higher frequencies and higher-performance levels.
In the field of automotive engineering, an increasing number of functions, previously accomplished mechanically, are now solved electronically: Braking and power steering are two examples.
Elsewhere in power electronics, thermal management becomes a critical consideration in the design of DC power supplies, inverters, power controllers and motor drivers.
But it is the exponential growth in LED technologies that is creating huge market demand for efficient, reliable, low-cost thermal management solutions. 3

4. What is “Watts per meter-Kelvin”?
“Heat flow across a surface per unit area per unit time, divided by the negative of the rate of change of temperature with distance in a direction perpendicular to the surface. Also known as Coefficient of Thermal Conductivity”
What does Watts per metre-Kelvin mean?
The heat flow across a surface per unit area per unit time, divided by the negative of the rate of change of temperature with distance in a direction perpendicular to the surface.
Also known as coefficient of heat conductivity.
Because it’s a coefficient, it needs to be considered in conjunction with thickness.
Thermal Impedance is proportional to the ratio of thickness to CTE
See the examples on the next slide.

5. Thermal Management Lexicon
in2
Thermal Impedance: ∆Cº- /watt
“The effective temperature rise per unit power dissipation above the temperature of a stated external reference point under conditions of thermal equilibrium. Also known as thermal resistance.”
Thermal Resistance: ƼC/watt
“A measure of an object's ability to prevent heat from flowing through it, equal to the difference between the temperatures of opposite faces of the body divided by the rate of heat flow. Also known as heat resistance.”
Thermal Conductivity: Watt/ k “A measure of the ability of a substance to conduct heat, determined by the rate of heat flow normally through an area in the substance divided by the area and by minus the component of the temperature gradient in the direction of flow.”
What does Watts per metre-Kelvin mean?
The heat flow across a surface per unit area per unit time, divided by the negative of the rate of change of temperature with distance in a direction perpendicular to the surface.
Also known as coefficient of heat conductivity.
Because it’s a coefficient, it needs to be considered in conjunction with thickness.
Thermal Impedance is proportional to the ratio of thickness to CTE
See the examples on the next slide. m2 5

6. How to Disperse Excess Heat?
Radiation/Convection;
- Passive/active energy transmission into immediate
environment
Conduction;
External heat-sink: Copper “ladder” add-on frame
Internal heat-sink: (Copper-INVAR-Copper)
Thermally conductive substrate (non-metallic)
Thermally conductive insulated metal substrate (IMS)
Radiation
Convection
Conduction
External heatsink
Internal heatsink
Thermally conductive substrate 6

7. How to Disperse Excess Heat?
Passive Heat Sink Active Heat Sink;
Radiation
Convection
Conduction
External heatsink
Internal heatsink
Thermally conductive substrate 7

8. Types of Thermally-conductive dielectric materials;
Pastes & Adhesives:
- Passive device thermal under-fill and encapsulation
- Passive device permanent mounting. (“Fralock”)
Substrate core and prepregs
- Woven-glass reinforced
- Non-reinforced dielectric
- Metal-clad & metal core substrate;
> (IMS, Aluminum, Copper, INVAR core)
Dielectric has the function of thermal conduction, insulation and bonding.
The dielectric is a laminating resin loaded with a thermal conductive ceramic filler.
It gives a good bond to the copper foil and to the metal substrate
It may be glass-reinforced or unreinforced
Aluminum substrate is most popular due to its better mechanical performance.
Alternative metal substrates include copper and steel plate. 8

9. Functions of Thermally-conductive Dielectric Materials (IMS);
Thermal conduction of extraneous heat away from active and passive electronic devices.
Electrical insulation of circuitry from chassis.
Adhesion – bonding copper to aluminium (IMS substrate) or heat-sinks to chip sets
Structural electronic thermally conductive platform.
Dielectric has the function of thermal conduction, insulation and bonding.
The dielectric is a laminating resin loaded with a thermal conductive ceramic filler.
It gives a good bond to the copper foil and to the metal substrate
It may be glass-reinforced or unreinforced
Aluminum substrate is most popular due to its better mechanical performance.
Alternative metal substrates include copper and steel plate.

10. Typical Thermal Conductivity Values;
What does Watts per metre-Kelvin mean?
The heat flow across a surface per unit area per unit time, divided by the negative of the rate of change of temperature with distance in a direction perpendicular to the surface.
Also known as coefficient of heat conductivity.
Because it’s a coefficient, it needs to be considered in conjunction with thickness.
Thermal Impedance is proportional to the ratio of thickness to CTE
See the examples on the next slide. 10

11. How to Disperse Excess Heat?
Thermally conductive PCB laminates and prepregs
Conventional PCB substrates are designed to have good electrical insulation.
They also tend to have good thermal insulation properties as well.
Thermally conductive printed circuit laminates and prepregs are now available.
The thermal conductivity is achieved by loading the resin with a thermally conductive ceramic filler.
These materials can be used to build multilayer PCB structures which can then be bonded to a heat-dissipating base.
Insulated Metal Substrates (IMS) are commercially available.
They offer cost effective performance with straightforward fabrication, good mechanical stability and a range of thermal conductivities to suit particular configurations.
The concept is not new - Materials have been available since the 1960s, but only recently has the volume demand driven the development of new and improved versions. IMS materials generally consist of a thermally conductive dielectric layer sandwiched between a copper foil and an aluminium plate.
The dielectric may be unreinforced, or woven-glass reinforced.

12. How to Disperse Excess Heat?
Thermally conductive insulated metal substrate (IMS)
Radiation
Convection
Conduction
External heatsink
Internal heatsink
Thermally conductive substrate 12

13. How to Disperse Excess Heat?
Radiation
Convection
Conduction
External heatsink
Internal heatsink
Thermally conductive substrate 13

14. Typical CTE Values for Thermally Conductive Materials;
What does Watts per metre-Kelvin mean?
The heat flow across a surface per unit area per unit time, divided by the negative of the rate of change of temperature with distance in a direction perpendicular to the surface.
Also known as coefficient of heat conductivity.
Because it’s a coefficient, it needs to be considered in conjunction with thickness.
Thermal Impedance is proportional to the ratio of thickness to CTE
See the examples on the next slide. 14

15. CTE differences Inherent in IMS Materials
CTE differences between copper, dielectric & aluminium highlighted during thermal cycling.
Power-on & power-off heating & cooling cycling.
Day/night & seasonal temperature & humidity variation.
Thermal Stress fatigue may ultimately cause cracking of solder joints, ceramic components, or delamination of substrate to aluminum.
In typical LED street lighting applications, the main reliability issue for insulated metal substrates is not dielectric breakdown, since operating voltages are relatively low, but the effect of shear stress resulting from CTE differences between copper, dielectric and aluminium and ceramic components during the severe thermal cycling between power-on and power-off, together with day-night and seasonal ambient temperature and humidity variation.
These stresses and strains may ultimately cause fatigue cracking of solder joints or ceramic components and delamination of the substrate. Glass reinforcement of the dielectric reduces the CTE mismatch between the substrate and the ceramic components reducing the failure rate of solder joints or component cracking through mismatched CTEs

16. Typical Characteristics of IMS laminates
Company
Material Type
Thermal Conductivity (W/m*K)
DuPont
CooLam LX
0.80
Arlon
91ML2380
1.00
Bergquist
CML-11006
1.10
99ML
Ventec
VT4A-1
1.30
MP-06503
92ML
2.00
HT-04503
2.20
VT-4A2
2.50
Laird
T-Lam SS 1KA04
3.00
VT-4A3
Printed circuit fabrication is by conventional print-and-etch techniques.
The aluminium is protected during etching by a peelable film, usually a PET or PI
Single-layer technology is suitable for most applications, but multilayer constructions are feasible by sequential lamination using thermally conductive prepregs, and thin laminates constructed from thermally conductive prepregs. Typical characteristics of IMS laminates are: Aluminium from 0.5 mm to 3.0 mm thick, available in different grades to suit mechanical requirements, copper from 18 um to 410 um , and dielectric thickness from 75 um to 150 um. Thermal conductivity 0.4 to 2.5 Watts per metre Kelvin. (Ventec products as 1.6 w/km and 2.2 w/km) there are products being sold as IMS for thermal management that use just FR4 PP for the dielectric, so have thermal conductivity of around 0.4 w/km and bring no benefit in terms of thermal conductivity
Copper is about 380W/mK, aluminium 200W/mK,and normal FR4 laminate in the region of 0.4W/mK 16

17. Characteristics of IMS laminates: Beware of Data Sheets
Characteristics of IMS laminates: Beware of Data Sheets! A Sampling of Data Sheet Test Methods;
Spec/Test Method
Intended Spec Purpose
ASTM F433-02:
Standard Practice for Evaluating Thermal Conductivity of Gasket Materials
* ASTM D :
Standard Test Method for Thermal Transmission Properties of Thermally
Conductive Electrical Insulation Materials
ASTM E :
Standard Test Method for Thermal Diffusivity by the Flash Method NA
No specification or test method listed
* Intended specification for use with Thermally Conductive Electrical Insulation Materials
Printed circuit fabrication is by conventional print-and-etch techniques.
The aluminium is protected during etching by a peelable film, usually a PET or PI
Single-layer technology is suitable for most applications, but multilayer constructions are feasible by sequential lamination using thermally conductive prepregs, and thin laminates constructed from thermally conductive prepregs. Typical characteristics of IMS laminates are: Aluminium from 0.5 mm to 3.0 mm thick, available in different grades to suit mechanical requirements, copper from 18 um to 410 um , and dielectric thickness from 75 um to 150 um. Thermal conductivity 0.4 to 2.5 Watts per metre Kelvin. (Ventec products as 1.6 w/km and 2.2 w/km) there are products being sold as IMS for thermal management that use just FR4 PP for the dielectric, so have thermal conductivity of around 0.4 w/km and bring no benefit in terms of thermal conductivity
Copper is about 380W/mK, aluminium 200W/mK,and normal FR4 laminate in the region of 0.4W/mK 17

18. Typical Characteristics of IMS Substrates
Single-sided, print-and-etch technology
Aluminium 0.5mm – 3mm (.020”-.120”) thick
Different grades (5052/6061) available to suit different applications
Different Alloys have significant differences in mechanical characteristics
Dielectric thickness 75μm – 150μm (.003”-.006”)
Copper thickness’; 18 μm+ (1/2 oz +)
Thermal conductivity ranges;
- Glass reinforced: 0.4 to 3.0 W/mK
- Up to 8+ W/mK available for non reinforced dielectrics
Printed circuit fabrication is by conventional print-and-etch techniques.
The aluminium is protected during etching by a peelable film, usually a PET or PI
Single-layer technology is suitable for most applications, but multilayer constructions are feasible by sequential lamination using thermally conductive prepregs, and thin laminates constructed from thermally conductive prepregs. Typical characteristics of IMS laminates are: Aluminium from 0.5 mm to 3.0 mm thick, available in different grades to suit mechanical requirements, copper from 18 um to 410 um , and dielectric thickness from 75 um to 150 um. Thermal conductivity 0.4 to 2.5 Watts per metre Kelvin. (Ventec products as 1.6 w/km and 2.2 w/km) there are products being sold as IMS for thermal management that use just FR4 PP for the dielectric, so have thermal conductivity of around 0.4 w/km and bring no benefit in terms of thermal conductivity
Copper is about 380W/mK, aluminium 200W/mK,and normal FR4 laminate in the region of 0.4W/mK

19. Primary IMS Aluminum Alloys 5052 & 6061
What does Watts per metre-Kelvin mean?
The heat flow across a surface per unit area per unit time, divided by the negative of the rate of change of temperature with distance in a direction perpendicular to the surface.
Also known as coefficient of heat conductivity.
Because it’s a coefficient, it needs to be considered in conjunction with thickness.
Thermal Impedance is proportional to the ratio of thickness to CTE
See the examples on the next slide. 19

20. PCB Fabrication considerations: Alloy Physical Differences
Alloyed With
Tensile
Elongation %
Yield
Brinell Hardness
5052 H32 Mg
33000
12%
28000 60
6061 T6
Mg+Si+Fe
44000
17%
41000 95
H-strain-hardened (wrought products only). Applies to products which have their strength increased by strain-hardening, with or without supplementary thermal treatments to produce some reduction in strength.
If you’re building multilayer constructions, rather than making straightforward single-sided circuits (And we also have customers who fabricate their own IMS laminate), you need to be aware that thermally conductive prepregs need the sort of press parameters you would use for a low-flow.
You can make the resin flow, if you’re quick with your heat-up and getting the pressure on. And with the right technique, you can encapsulate 2oz tracks.
You have to try harder if you want to fill patterns deeper than 2oz.
T-applies to products which are thermally treated, with or without supplementary strain-hardening, to produce stable tempers. 20

21. PCB Fabrication considerations: Lamination
Heavy filler loading leads to differing prepreg flow characteristics at lamination;
- Moderately less flow than “standard” prepreg materials
> No fill required, therefore less flow not a process concern
- Aluminum-FR4 lamination bonds materials with
highly differing CTE rates;
> Low/slow rates of cooling at conclusion of cure segment
are advised.
> “Pin-less Lamination” requires caution in tooling stack heights.
If you’re building multilayer constructions, rather than making straightforward single-sided circuits (And we also have customers who fabricate their own IMS laminate), you need to be aware that thermally conductive prepregs need the sort of press parameters you would use for a low-flow.
You can make the resin flow, if you’re quick with your heat-up and getting the pressure on. And with the right technique, you can encapsulate 2oz tracks.
You have to try harder if you want to fill patterns deeper than 2oz. 21

22. PCB Fabrication considerations: Drilling
Tendency to rapid tool wear due to presence of thermal filler and aluminum.
Drill bits with under-cut geometry preferred
Chip loads 50-60% of that used for FR4
Spindle speeds 60-70% of that used for FR4
Drilling from copper side generally more successful in avoiding exit/entry burrs.
With ceramic dielectrics, recommended spindle speeds should be reduced by 20%.
Tool life will be reduced by approximately half in comparison to FR4 dielectrics.
Minimal lubrication may give benefits
Talk to your tool supplier

23. IMS PCB Fabrication considerations: Routing
Rapid tool wear a significant Issue
General Parameter Recommendations;
- Router RPM speed; 15,000 to 20,000 RPM
- Table Feed; IPM
- Router Type:
- Carbide or Diamond coated 2-flute end mill best option.
- Tools (2 or 3 flute end-mills) tend to pull out of collet.
- No vacuum path required/desired
- Change backer with each new pass.
Break-away tabs do not need to be as wide as
in standard designs for FR4 laminates.
> Scoring across break-away tabs may be effective to assist
in part removal with minimal “flash” removal required.
With ceramic dielectrics, recommended spindle speeds should be reduced by 20%.
Tool life will be reduced by approximately half in comparison to FR4 dielectrics.
Minimal lubrication may give benefits
Talk to your tool supplier 23

24. IMS PCB Fabrication considerations: Array Scoring
Scoring Aluminum-FR4 IMS composite a Challenge
Suggested Starting Parameters;
- Scoring Blade RPM range: 1,500 – 2,500 RPM
- Scoring Head/Table IPM range: IPM
- Blade Tooth Count: 35-70
> 1-3 blade passes, dependent upon cut depth & material thickness.
- Lubricant use very helpful: (“Tap Magic: Aluminum”).
- Scoring across routed array tabs is a good design
practice in Al substrate array designs.
With ceramic dielectrics, recommended spindle speeds should be reduced by 20%.
Tool life will be reduced by approximately half in comparison to FR4 dielectrics.
Minimal lubrication may give benefits
Talk to your tool supplier 24

25. PCB Fabrication considerations: Solder Mask
Much of the surge of interest in IMS is LED Lighting demand.
LED Lighting in visual ranges often requires white solder mask as a reflecting surface to enhance brightness.
White LPI Solder Masks often brown after assembly due to exposure to flux chemistries and heat in combination.
- White LPI does hold up as well as desired, and becomes brittle when cured
sufficiently to avoid pink/purple assembly discoloration.
- Two newer white masks have shown promise in resisting discoloration;
> Peters (SD2491SM TSW)
> Sun Chemicals (CAWN 2589/2591)
If you’re building multilayer constructions, rather than making straightforward single-sided circuits (And we also have customers who fabricate their own IMS laminate), you need to be aware that thermally conductive prepregs need the sort of press parameters you would use for a low-flow.
You can make the resin flow, if you’re quick with your heat-up and getting the pressure on. And with the right technique, you can encapsulate 2oz tracks.
You have to try harder if you want to fill patterns deeper than 2oz.

26. IMS Compatibility with lead-free soldering and thermal cycling
Reliability influenced by construction & manufacturing process of IMS.
Glass reinforced dielectric has lower Z-axis CTE than non-reinforced materials.
Wide range in Tg values in currently available thermal substrates;
- Resin chemistry determines Tg and Td
Insulated metal substrates are generally compatible with lead-free soldering processes.
Construction has a significant influence on reliability.
Woven glass reinforcement of the dielectric reduces its coefficient of thermal expansion both in the XY plane
Resin chemistry determines characteristics, such as Tg (glass transition temperature) and Td (decomposition temperature), which, likewise, affect reliability under thermal stress and thermal shock conditions.
Surface treatment of aluminium prior to bonding is critical, both to achieve high bond strength and to avoid high-resistance shorts from metallic debris. 26

27. Compatibility with lead-free soldering and thermal cycling
Surface treatment of aluminium critical in thermal shock performance
- Mechanical or chemical roughening of surface
μm Rz surface roughness desired for mechanical
bond strength.
Presence of moisture is critical at Pb-free HASL assembly; Higher internal vapour pressures are generated as the moisture is expelled during reflow operations.
Desiccate!
Insulated metal substrates are generally compatible with lead-free soldering processes.
Construction has a significant influence on reliability.
Woven glass reinforcement of the dielectric reduces its coefficient of thermal expansion both in the XY plane
Resin chemistry determines characteristics, such as Tg (glass transition temperature) and Td (decomposition temperature), which, likewise, affect reliability under thermal stress and thermal shock conditions.
Surface treatment of aluminium prior to bonding is critical, both to achieve high bond strength and to avoid high-resistance shorts from metallic debris.

28. Compatibility with lead-free soldering and thermal cycling
Desiccate prior to Assembly!
Bake panels;
Time: minutes (at temp)
Temp: 225º – 235º F (107º- 113º C)
Stack (preferred): 1-1.5” (25.4 – 38 mm)
Rack: Use only vertical racks with support the full
height of panels.
Insulated metal substrates are generally compatible with lead-free soldering processes.
Construction has a significant influence on reliability.
Woven glass reinforcement of the dielectric reduces its coefficient of thermal expansion both in the XY plane
Resin chemistry determines characteristics, such as Tg (glass transition temperature) and Td (decomposition temperature), which, likewise, affect reliability under thermal stress and thermal shock conditions.
Surface treatment of aluminium prior to bonding is critical, both to achieve high bond strength and to avoid high-resistance shorts from metallic debris. 28

29. Summary
Increasing interest in cost-effective thermal management of electronics;
- IMS-type materials are the board-level solution.
Choose materials to suit the application
- Many different levels of thermal relief available.
Do your own qualification tests, and don’t take data sheet values too literally.
- Ventec VT4A-1 data sheets under-state the thermal capabilities of the material.
(Just read the slide)

30. Thank you for your attention!