power integrity guidelines samtec pet/pes series connector...

Copyright © 2008 Teraspeed Consulting Group LLCCopyright © 2008 Samtec, Inc

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Power Integrity Guidelines Samtec PET/PES Series Connector Measurement and Simulation Data

Scott McMorrow, Director of Engineering



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PET/PES Power Integrity Guidelines Test & Evaluation Board Set



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PET/PES Power Integrity GuidelinesModeled Section

PES/PET Power Integrity Test and Evaluation System

Split in plane

PET BoardPES Board

Split in plane

Thermal Spoke Plane

Contacts

Direct Plane Contacts

PES Board

PET Board

Thermal Spoke Plane

Contacts

Thermal Spoke Plane

Contacts

Direct Plane Contacts

Multiple Test PointsMultiple Test Points



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PET/PES Power Integrity Guidelines Test Board Layer Stackup

Layer ThicknessCross

Section Layer Definition Material Type

0.5 mil Solder Resist

0.8 mil Cu Plating

1 1.2 mil Plane 1 oz

58 mil Core FR4

2 1.2 mil Plane 1 oz

0.8 mil Cu Plating

0.5 mil Solder Resist

63 mil Finished Thickness



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PET/PES Power Integrity Guidelines

• The PES/PET Power Integrity test and evaluation system is comprised of two test boards connected together by dual PES/PET connectors

• This board set is designed for the precision measurement of contact, breakout, via, and plane spreading resistance, as encountered in realistic system applications.



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PET/PES Power Integrity Guidelines Measurements

• The PES/PET Power Integrity test and evaluation system is designed to facilitate measurements from a precision Milli-Ohm meter, such as an Instek GOM-802, utilizing Kelvin 4-wire probe techniques.



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PET/PES Power Integrity Guidelines Modeling and Simulations

• PES/PET Power Inegrity modeling and simulations were performed with the DC modeler available in Ansoft SIWave.



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PET/PES Power Integrity Guidelines Test Structures

• Serial via resistance– Arrays of 40 vias with 53 mil finished hole diameter are available for

the accurate measurement of average via resistance, with the inclusion of attach traces.

– Also used for the accurate adjustment of PCB fabrication parameters for modeling and simulation purposes.

• Copper thickness• Via barrel plating thickness



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• Daisy Chained Connector Pin Array– A serial connection of 6 PES/PET contacts is used for the

measurement of average contact resistance, including the increased resistance due to attach vias.



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PET/PES Power Integrity GuidelinesTest Structures - Daisy Chained Connector Sections

PES/PET Power Integrity Test and Evaluation System

6 daisy chained connector sections are interconnected

between two boards.

Test Point Test PointPES Board

PET Board



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• Direct Plane Attach– Two connector contacts are attached directly to the top

and bottom plane. – Measurement locations are provided for several points

across the plane on both attached boards.



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• Contact Types– Two plane contact types are used.

• Direct plane connection– Best DC resistance

• Thermal spoke plane connection– Improved manufacturability and rework

– Slightly increased DC resistance

Direct Connect Thermal Spoke



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PET/PES Power Integrity Guidelines Documentation Goals

• Provide Information for :– DC characterization of the PES/PET power

connector system.• Accurate measurement of “real world” per contact

resistance.• Include mounted breakout resistivity.• Include via resistivity.• Correlate simulation to measurements



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PET/PES Power Integrity Guidelines A Simple Problem

– Via test strip contains• 40 - 52 mil vias• 39 – trace connections between vias• 2 – trace connections from test point to via

array.• 40 – Via/Trace overlaps

– 40 Vias• 52 mil hole• 1.65 mil plating

– 39 Via-to-via trace connections• 90 mil trace width• 2 mil trace thickness• 48 mil trace length

– 2 Test point-to-via trace connection• 90 mil trace width• 2 mil trace thickness• 123 mil trace length

– 40 Via/Trace overlaps• 40 via/trace overlapping areas• Via increases effective trace resistance



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PET/PES Power Integrity GuidelinesSimplified Incremental Modeling of Vias Connected by Traces

Model as Rectangular

Trace


Trace


TraceModel as Via Model as Via



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PET/PES Power Integrity GuidelinesVia/Trace Overlap Model Approximation

– Model as a trace and then scale for surface area lost.– Assume that negligible current flows on far side of via trace.

• This assumption is confirmed by 3D finite element simulation.• Resistance of Trace = Resistivity x length/Area• Surface Area of Trace = Via Inner Diameter x Via Pad Diameter / 2• Surface Area of Via Hole = π x Via Diameter 2 / 2• Scale Factor = (Surface Area of Trace – Surface Area of Via Hole) / Surface Area of Trace



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PET/PES Power Integrity Guidelines Via Resistance Calculation

• The resistance of a via can be approximated by calculating the resistance of the equivalent rectangular volume described by the following: – Via Resistance = Resistivity x Length of Via / Area of Via Plating– Area = pi x (Inner diameter + Plating thickness) x Plating

thickness– Resistivity of Copper = 1.7e-6 Ω-cm (.67e-6 Ω-in)

• For a 52 mil via hole 62 mils long with 2 mil plating• Via Resistance = .67E-6 x .062 / π x (.052 + .002) x .002• Via Resistance = 122 µΩ



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PET/PES Power Integrity GuidelinesVia-to-Via Trace Resistance Calculation

• The resistance of a trace can be calculated by the following standard formula:– Trace Resistance = Resistivity x Length of trace / Area of trace– Area = Trace Width x Total Thickness (copper + plating)– Resistivity of Copper = 1.7e-6 Ω-cm (.67e-6 Ω-in)

• For a 48 mil long trace, 90 mil wide, with 2 mil thickness• Trace Resistance = .67E-6 x .048 / (.090 x .002)• Trace Resistance = 179 µΩ



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PET/PES Power Integrity GuidelinesTest Point-to-Via Trace Resistance Calculation


• For a 143 mil long trace, 65 mil wide, with 2 mil thickness• Trace Resistance = .67E-6 x .123 / (.090 x .002)• Trace Resistance = 458 µΩ



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PET/PES Power Integrity GuidelinesVia/Trace Overlap Resistance Calculation


• For a 26 mil long trace, 90 mil wide, with 2 mil thickness• Trace Resistance = .67E-6 x .026 / (.090 x .002)• Trace Resistance = 97 µΩ• Surface Area of Trace = .052 x .090/2 = 2.34e-3• Surface Area of Via Hole = π x (.052/2) 2 /2 = 1.062e-3• Scale Factor = (2.34e-3 - 1.062e-3) / 2.34e-3 = .546• Resistance = 178 µΩ



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PET/PES Power Integrity Guidelines52 mil Via Test Array Resistance Calculation

• The resistance of the via array is calculated as follows:– 40 Vias

• 40 x 122 µΩ = 4.88 mΩ (24.5%)– 39 Via-to-via trace connections

• 39 x 179 µΩ = 6.98 mΩ (35.1%)– 2 Test point-to-via trace connection

• 2 x 458 µΩ = 0.916 mΩ (4.6%)– 40 Via/Trace overlaps

• 40 x 178 µΩ = 7.12 mΩ (35.8%)

• Total 19.90 mΩ (100%)

Key Point: Breakout traces attached to vias contribute 75% of the via resistance.



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PET/PES Power Integrity GuidelinesVia Array Resistance Measurements

159 µΩ

Ansoft Extracted Via Barrel

Resistance

510 µΩ

Average Linear Via

Interconnect Resistance

351 µΩ

Residual non-Via

Interconnect Resistance

19.38 mΩ (19.9 by hand)21.9 mΩ52 mil

40 Via Resistance Simulated

Ansoft SIWave

40 Via ResistanceMeasured

Via

Linear Via Interconnect Resistance – the resistance of the via barrel, pad and connecting trace, calculated by removing the test trace resistance from the 40 via measured resistance and dividing by 40.

Via Barrel Resistance – the resistance of the via barrel by itself.

Residual non-via interconnect resistance – the resistance of the pad and connecting trace for one via, calculated by subtracting the barrel resistance from the linear resistance.



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PET/PES Power Integrity GuidelinesDaisy Chained Resistance Test of 6 Contacts

----1.18 mΩ---------Test Point Trace Direct Connect to Pads

----

3.96 mΩ

3.22 mΩ

Measured Resistance with Test Point

1.39 mΩ

----

----

Simulated Resistance

---------Test Point Trace Thermal Spoke to Pads

428 µΩ

340 µΩ

Average Resistance per Contact (with

mounting)

----Direct Plane Connect

62 µΩThermal Spoke Connect

Average Additional Resistance of 8 Parallel

Thermal Spokes (12 per daisy chain)

Connection Type

Specified connector contact resistance 280 to 440 µΩ.

Mounting adds up to 60 µΩadditional resistance for a direct connect contact and 150 µΩ for a Thermal Spoke contact, including vias and copper.



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PET/PES Power Integrity GuidelinesDaisy Chained Resistance Test

• The chained resistance test provides a reasonable estimate of the total mounted contact resistance for a connector that is mounted to small fill areas of limited size.

– Most interconnect resistance can be calculated using trace resistance calculations. (see slides 10-17)

• Resistance of Trace = Resistivity x length/Area

– Mounted contact resistance (one mated contact), for the direct connect case, can be estimated from the previous slide as 500 µΩ maximum, if we assume that the connector contact resistance is at it’s upper limit of 440 µΩ.

• At rated current of 35.9A for a 30C temperature rise, this would amount to a voltage drop across the connector of 17.95 mV, and a total power dissipation of 644 mW per mated contact.

– Mounted contact resistance (one mated contact), for the Thermal Spoke connect case, can be estimated from the previous slide as 590 µΩ maximum, if we assume that the connector contact resistance is at it’s upper limit of 440 µΩ.

• At rated current of 35.9A for a 30C temperature rise, this would amount to a voltage drop across the connector of 21.2 mV, and a total power dissipation of 760 mW per mated contact.



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PET/PES Power Integrity GuidelinesResistance from Plane to Pad (Bottom Layer Attach)

0.81 / 0.608 mΩPES/PETShort Path

Thermal Spoke Connect

0.69 / 0.566mΩPES/PETShort Path

Direct Connect

1.06 / 0.855 mΩPES/PETLong Path

Thermal Spoke Connect

0.914 / 0.812 mΩ

PES/PETLong Path

Direct Connect

Measured vs. Simulated

Connection Type



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PET/PES Power Integrity GuidelinesCurrent Density Plot (Plane to Contact Pad)



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Measurement uncertainty due to difficult test probes is larger than actual contact resistance.

Specified connector contact resistance is 280 to 440 µΩ.

Mounting and plane spreading resistance is dominant.

This will be significant for power systems using multiple contacts!

PET/PES Power Integrity GuidelinesDirect Plane Attach (1 contact)

1.99 / 2.08mΩ1.69 / 1.77mΩPlane-to-Plane Mated Through One Contact

0.914 / 1.06 mΩ0.69 / 0.81 mΩPlane to PET Connector Pad

162 / 0 µΩ

0.914 / 1.06 mΩ

Measured ResistanceShort Path

(direct/thermal)

0.69 / 0.81 mΩPlane to PES Connector Pad

310 /160 µΩContact Resistance(Calculated)

Measured ResistanceLong Path

(direct/thermal)

Connection Type



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PET/PES Power Integrity GuidelinesDirect Plane Attach Resistance Test (1 contact)

• The direct plane attach resistance test provides a reasonable estimate of the total mounted contact resistance for a connector that is mounted through vias on large planes.– Resistance of plane spreading resistance and attachments

dominates the total resistance.– Measurement uncertainty, due to difficult test probes and points,

is larger than actual contact resistance.• Since attach and plane spreading resistance dominates, this is not an

issue.

– For multiple contact power systems the focus needs to be on the resistive loss through the planes.



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PET/PES Power Integrity GuidelinesPowering Multiple Contacts

• When multiple contacts on a power connector system are used, power delivery is mostly accomplished by one or multiple planes within a PCB.– Plane attach resistance measurements and simulations from the

previous section apply ONLY to the case where one contact is powered from a given plane, with no current path sharing to other contacts.

• When multiple contacts are powered from the same plane, current path sharing increases the resistance seen through each contact.

• Because of this, it is necessary to either de-rate the resistance, or to simulate this with appropriate software that can model DC drop.



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PET/PES Power Integrity GuidelinesCurrent Density Plot (One Contact Excited @ 1 A)



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PET/PES Power Integrity GuidelinesCurrent Density Plot (Seven Contacts Excited @ 1 A each)

4.8” x 4.8” PCB.

2 mil thick copper plane.

Connector mounted on top side of PCB near edge of board.

Power plane at bottom of board 58 mils from top.

8 x 52 mil via connections to each power blade

200 mil via used for power delivery to plane, spaced 3.5”away from connector.

Multiple current sources used to inject 1A current into each contact individually.



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Connector connections to planes experience current sharing, which increases the path resistance to each contact. As more contacts are added, this additional resistive loss must be accounted for, either through measurement or simulation.

Connectors placed at the edge of a PCB exhibit current starvation on the outside edge of the board, because the current required for all connector contacts must be diverted around the edge and share the same path. Current densities become higher in these cases.

PET/PES Power Integrity GuidelinesCurrent and Voltage Gradient (Seven Contacts Excited)



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PET/PES Power Integrity GuidelinesAverage Thermal Spoke Via Attach Resistance Results

0.753.001.500.906.290.442.937

0.783.111.560.935.600.442.586

0.813.241.620.974.860.442.215

0.863.431.721.034.120.441.844

0.933.701.851.113.330.441.453

1.064.232.121.272.540.441.052

1.405.582.791.671.670.440.621

Total Parallel

Resistance (2 x 1 Oz

Cu)

Total Parallel

Resistance (1/2 Oz Cu)

Total Parallel

Resistance (1 Oz Cu)

Total Parallel

Resistance (2 mil Cu)

Plane-to-Plane Resistance per Contact (mΩ)

PES/PET Resistance per Contact (mΩ)

Attach Resistance (per PCB)

# Contacts



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PET/PES Power Integrity GuidelinesParallel Power Resistance w/ Recommend Thermal Spoke Vias

Current sharing on the power plane(s) ultimately limits the lowest resistance that can be achieved through a power connector.

As additional connector contacts are added to the plane, parallel resistance reduces asymptotically.

These results are valid for only the tested configuration. Other architectures should be validated through measurement or simulation.

PES/PET Parallel Power Resistance

0.00

1.00

2.00

3.00

4.00

5.00

6.00

1 2 3 4 5 6 7

(Number of Contacts)

Res

ista

nce

(mΩ

) Total Parallel Resistance (2 mil Cu)

Total Parallel Resistance (1 Oz Cu)

Total Parallel Resistance (1/2 Oz Cu)

Total Parallel Resistance (2 x 1 Oz Cu)



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PET/PES Power Integrity GuidelinesAverage Direct Contact Attach Resistance Results

0.742.971.480.896.230.442.907

0.773.081.540.925.540.442.556

0.803.191.600.964.790.442.185

0.843.381.691.014.050.441.814

0.913.641.821.093.270.441.423

1.034.132.071.242.480.441.022

1.365.452.721.631.630.440.601

Total Parallel

Resistance (2 x 1 Oz Cu)

Total Parallel

Resistance (1/2 Oz Cu)

Total Parallel

Resistance (1 Oz Cu)

Total Parallel

Resistance (2 mil Cu)

Plane-to-Plane Resistance per Contact (mΩ)

PES/PET Resistance per Contact (mΩ)

Attach Resistance (per

PCB)# Contacts



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PES/PET Power Resistance Comparison (with and without Thermal Ties)

0.80

0.90

1.00

1.10

1.20

1.30

1.40

1.50

1.60

1.70

1.80

1 2 3 4 5 6 7

Number of Contacts

Res

ista

nce

(mΩ

)

Thermal Tie ViaDirect Contact Via

PET/PES Power Integrity GuidelinesDirect Via Attach vs. Thermal Spoke Connection to Plane

Current is delivered through the planes 3.5 inches away from the connector.

Previous measurements, and current simulations, show that plane spreading resistance dwarfs any resistance advantage to using non-thermal spoke vias.

Plane spreading inductance continues to dominate multiple contact power delivery systems.



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PET/PES Power Integrity GuidelinesThermal Spoke Connection through 2 mil Cu Plane Voltage Drop vs. Current

Plane spreading resistance and current path sharing dominate the voltage drop through the PES/PET system.

This plot represents a one-way current path from one board to another through PES/PET mated connectors. Total voltage drop for a ground and power system would incorporate a round-trip current loop, and would be double the total voltage drop from these curves.

PES/PET Thermal Spoke Attach Through 2 mil Cu PlaneVoltage Drop vs. Current

0

20

40

60

80

100

120

140

160

180

1 2 3 4 5 6 7

Number of Contacts

Volta

ge D

rop

(mV) 1 Amp

10 Amp25 Amp50 Amp75 Amp100 Amp



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PES/PET vs. HPM/HPF Power Integrity GuidelinesContact Efficiency Comparison

Simulations and measurements show that the PES/PET power connector system is 3 times more efficient than the HPM/HPF.

By design, the PES/PET connector will allow for 3 times the current density per mated contact as the HPM/HPF connector.

< 1 mΩ total roundtrip DC resistance achievable with multiple PES/PET contacts and multiple power/ground planes.

PES/PET vs. HPM/HPF Total Path Resistance Comparison 2 mil Cu Planes

0.5

1.0

1.5

2.0

2.5

3.0

3.5

1 2 3 4 5 6 7

Number of Contacts

Res

ista

nce

(mΩ

)

HPM/HPFPES/PET



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PET/PES Power Integrity GuidelinesSummary

• Key PES/PET conclusions:– Attach resistance (pads, vias, breakout traces,

plane spreading resistance) dominates.– Current sharing on planes between multiple

contacts reduces connector power efficiency.– Negligible difference between direct plane

contact and thermal spokes.• < 1 mΩ DC power/ground resistance achievable

with multiple PES/PET contacts and multiple 1 oz Cu power/ground planes

power integrity guidelines samtec pet/pes series connector...

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