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BUILDING HDI STRUCTURES USING THIN FILMS AND LOW TEMPERATURE SINTERING PASTE James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits Chris Hunrath – Integral Technology

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BUILDING HDI STRUCTURES USING THIN FILMS AND LOW TEMPERATURE SINTERING PASTE. James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits Chris Hunrath – Integral Technology. Two Basic elements of a PCB. HDI- Driving more connections. 1704 PIN BGA 33 x 33 mm 1.0 mm pitch. - PowerPoint PPT Presentation

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Page 1: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

BUILDING HDI STRUCTURES USING THIN FILMS AND LOW TEMPERATURE SINTERING PASTE

James Haley – Ormet CircuitsCatherine Shearer – Ormet CircuitsChris Hunrath – Integral Technology

Page 2: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Two Basic elements of a PCB

Page 3: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

HDI- Driving more connections

3

144 PIN BGA

11 x 11 mm0.5mm pitch

1704 PIN BGA33 x 33 mm1.0 mm pitch

Page 4: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Sequential Build-Up

• Structure is layered 1 at a time on each side.

• Allows unrestricted via placement.

• Requires repeated trips through the PCB manufacturing process.

Page 5: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Changing the Build-Up Sequence

• Via formation before lamination– Buried vias

• Copper plated through holes and vias.• No connections formed during the lamination cycle.

– Z-axis connections other than plated copper• Conductive material is applied to individual layers.• Connection is made during lamination.• There are several methods and materials to do this.

Page 6: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Conductive Pastes for Z-axis connections

• Many different types are curable at PCB temperatures.

• Particle to particle connection made when polymer matrix cures and shrinks.

• Most do not sinter.

Page 7: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Sintering• Sintering refers to a process where a mixture of particles is

fused together, usually thermally.

• Thermal sintering usually happens at high temperatures (>800ºC).

• Sintering mixtures can be used for structures, dielectrics as well as conductors.

• If sintering can be done at temperatures compatible with organic PCB laminating temperatures, strong bonds can be formed.

Page 8: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Transient Liquid Phase Sintering• Transient Liquid Phase Sintering takes advantage of the fact that a

liquid metal will interdiffuse with a non-molten metal to form a solid metallurgical joint at relatively low temperatures.

• Interdiffusion starts at 150ºC– Well with in the range of PCB lamination.

• This type of interdiffusion – in this case between copper and tin – results in a metallurgical bond between the two metals that is stronger than a mere particle surface-to-layer contact.

Page 9: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Sintering is not the same as melting.What happens at assembly temperatures.

Sintered Interconnect Matrix Components

Melting Point(C)

Percentage of Matrix

Cu 1085

>85%Cu6Sn5 415

Cu3Sn 640

Bi 271 < 15%

Page 10: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Forming Conductors in B-Stage

• Allows changes in PCB processing sequence.

• TLPS is applied to B stage layer before lamination.

• B-Stage for TLPS material needs do the following;– Laser drill compatible.– Maintain B stage properties through paste process steps.– Bond and flow in the z-axis.– Keep TLPS paste in place until sintered.– CTE, Td compatible with lead free assembly.

Page 11: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Standard B Stage

• Not made for B Stage processing– Pre-tacking– Laser drilling– TLPS paste drying

Page 12: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

B-Stage Structures• Glass cloth in prepreg is integral to both it’s B stage and C stage

characteristics.– Allows handling of B stage form– Controls flow and pressed thickness

• Standard processing allow opportunities for undesirable paste flow through gaps in glass.

Page 13: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Film for TLPS Interconnects• Replace the glass with a polymer matrix.

– Holds the paste particles in place until sintered (final lamination)

• Use a Second polymer to provide bonding and high temperature characteristics.

• Second polymer does not cure during initial paste processing.– Pre-tacking– Laser drilling– Paste drying

Page 14: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

TLPS Interconnect in Film

Page 15: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Metallurgical Bond to Copper Layers

• Matrix keeps high temperature B stage polymer from interfering with paste/layer interaction.

Page 16: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

TLPS Paste and Film create thermally stable structure

As is 1x 2x 3x 4x 5x 6x "+60 sec

0123456

Daisy chain test vehicle of 120 paste viasResistance change after 10 sec float @ 288°C

4 mil 6 mil 8 mil

Ohm

s

via diameter >

Page 17: James Haley – Ormet Circuits Catherine Shearer – Ormet Circuits

Conclusion• TLPS materials provide metallurgical bonds to both particles

within the paste and the copper foil circuits of various PCB layers.

• Dielectric materials should be chosen carefully for use with TLPS pastes.

• Films can offer processing and reliability advantages if;– Flow characteristics allow good paste sintering.– B stage properties can be maintained through paste processing.– Cure properties of the film provide thermal performance.

• In combination, the paste and film offer copper plating like reliability while enabling beneficial changes in HDI PCB construction.