©ventec electronics thermally conductive substrates; a rapidly growing pcb mfg opportunity

©VENTEC ELECTRONICS

Thermally Conductive Substrates;

A Rapidly Growing PCB Mfg Opportunity


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.

Thermal Management Requirements Increasing in Demand in the Marketplace


(Almost)

Everywhere lighting is in use, LED designs will replace it

within 5-8 years.

Thermal Management Requirements Increasing in Demand in the Marketplace


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”


Thermal Management Lexicon

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: ∆ºC/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.”

in2

m2


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)



Passive Heat Sink Active Heat Sink;


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)


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.


Typical Thermal Conductivity Values;

0

100

200

300

400

500

W/m.K

FR4 Steel Aluminum Copper Silver

Thermal Conductivity



Thermally conductive PCB laminates and prepregs



Thermally conductive insulated metal substrate (IMS)


Typical CTE Values for Thermally Conductive Materials;

0

5

10

15

20

25

ppm/ºC

FR4* Steel Aluminum Copper Silver

CTE Values: Thermally Active Materials


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.


Typical Characteristics of IMS laminates

Company Material TypeThermal

Conductivity (W/m*K)

DuPont CooLam LX 0.80

Arlon 91ML2380 1.00

Bergquist CML-11006 1.10

Arlon 99ML 1.10

Ventec VT4A-1 1.30

Bergquist MP-06503 1.30

Arlon 92ML 2.00

Bergquist HT-04503 2.20

Ventec VT-4A2 2.50

Laird T-Lam SS 1KA04 3.00

Ventec VT-4A3 3.00


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 D5470-06: Standard Test Method for Thermal Transmission Properties of Thermally

Conductive Electrical Insulation Materials

ASTM E1461-07: 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


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


Primary IMS Aluminum Alloys5052 & 6061

Ma

gn

esiu

m

Sili

co

ne

Zin

c

Ch

rom

ium

Ma

ng

an

ese

Tita

niu

m

Co

pp

er

Iro

n

5052

6061

0.00

0.50

1.00

1.50

2.00

2.50

Alloy Content: Remaining 3%

5052

6061


PCB Fabrication considerations: Alloy Physical Differences

Alloy

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.

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.

T-applies to products which are thermally treated, with or without supplementary strain-hardening, to produce stable tempers.


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.


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.


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; 12-15 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.


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: 15-25 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.


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)


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


Compatibility with lead-free soldering and thermal cycling

Surface treatment of aluminium critical in thermal shock performance

- Mechanical or chemical roughening of surface

- 5-25 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!


Compatibility with lead-free soldering and thermal cycling

Desiccate prior to Assembly!Bake panels; Time: 60 - 90 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.


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.


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©ventec electronics thermally conductive substrates; a rapidly growing pcb mfg opportunity

Documents

ventec electronics functions

ventec electronics types

excess heat

thermal resistance

thermal cycling

passive heat

automotive electronics

thermal diffusivity