james haley – ormet circuits catherine shearer – ormet circuits
DESCRIPTION
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 PresentationTRANSCRIPT
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BUILDING HDI STRUCTURES USING THIN FILMS AND LOW TEMPERATURE SINTERING PASTE
James Haley – Ormet CircuitsCatherine Shearer – Ormet CircuitsChris Hunrath – Integral Technology
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Two Basic elements of a PCB
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HDI- Driving more connections
3
144 PIN BGA
11 x 11 mm0.5mm pitch
1704 PIN BGA33 x 33 mm1.0 mm pitch
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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.
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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.
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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.
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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.
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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.
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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%
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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.
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Standard B Stage
• Not made for B Stage processing– Pre-tacking– Laser drilling– TLPS paste drying
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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.
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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
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TLPS Interconnect in Film
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Metallurgical Bond to Copper Layers
• Matrix keeps high temperature B stage polymer from interfering with paste/layer interaction.
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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 >
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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.