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Effects of Device Packaging and PC Board Materials on Radiation Dose in the Die

Edward R. Long, Jr.Longhill Technologies, inc.

Waynesboro, VA

540-363-0104LonghillTechnologies@PolyRAD.net

2004 MAPLDRonald Reagon Building & International Trade Center

Washington, DCSeptember 8-10, 2004Session P, Paper 150

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Presentation Outline

Aspects of spacecraft and on-board electronics that contribute to radiation shielding

What was modeled for total dose A single electronics board populated with a 3 X 5 array of microelectronic devices

whose packaging are plastic or ceramic (with and without lids), each of which are represented with several degrees of supplemental shielding and the board is studied with and without a 4-oz copper ground plane

Dose-at-the-die for the array of devices for two board locations in two spacecraft designs Three orbital environments: GSO, GTO, and SSO

Discussion of the resultsEffects of packaging, PCB, and shielding on TID

Implications for dosimeter measurements

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Aspects of Spacecraft and On-board Electronics

That Contribute to Radiation Shielding Aspects discussed in an earlier presentation1

Board location Where on the spacecraft Which board in an ordered stack of boards

Board Orientation Device position

Location on the board Adjacent devices

The structure, materials, and location of other on-board components

Aspects discussed in this presentation Device packaging materials

Plastic Ceramic

PCB materials No ground plane 4-0z Cu ground plane

Supplementary shielding 10-mil, 20-mil, 40-mil, and 80-mil PolyRAD

Two inward-facing board locations (between –X shear panel and –X battery)Near –X shear plane Near –X battery

1. - Long, Edward R., Jr., Modeling the Requirements for Radiation Shielding, 2003 MAPLD International Conference, Washington, DC, September 9-11, 2003

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Description of the Dose Modeling Two spacecraft designs

A Generic spacecraft1

Three-Quarter view

Intrinsic shielding equivalent to 0.135-in aluminum

Thin-walled version of the generic spacecraftIntrinsic shielding equivalent to 0.040-in aluminum

1. - Long, Edward R., Jr., Modeling the Requirements for Radiation Shielding, 2003 MAPLD International Conference, Washington, DC, September 9-11, 2003

Exterior instruments

Solar panel

Tanksupport panel Shear

panel

Anti-bucklepanel

-X Battery

Internal component

Instrumentsupport panel

Tanks

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Orbits GSO: 35800 km x 35800 km x 0 deg GTO: 36000 km x 300 km x 7 deg SSO: 800 km x 800 km x 98 deg

Single electronics board consisting of a 3 X 5 array of copies of a device, modeled with plastic and ceramic encapsulation (packaging).

Description of the Dose Modeling(continued)

Column 1 (plastic

encapsulate)

Column 2, (alumina

encapsulate, with kovar

lid)

Column 3, (alumina encapsulate, without kovar lid)

Non- shielded Row

10-mil PolyRAD

Shielded row

0.062-in FR4

0-oz or 4-oz copper ground plane

10-mil PolyRAD

Shielded row

10-mil PolyRAD

Shielded row

10-mil PolyRAD

Shielded row

Sketch is not to scale

kovar liddie

Column 1 (plastic

encapsulate)

Column 2, (alumina

encapsulate, with kovar

lid)

Column 3, (alumina encapsulate, without kovar lid)

Non- shielded Row

10-mil PolyRAD

Shielded row

0.062-in FR4

0-oz or 4-oz copper ground plane

20-mil PolyRAD

Shielded row

40-mil PolyRAD

Shielded row

80-mil PolyRAD

Shielded row

kovar liddie

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Cross section of modeled device, shown using ceramic encapsulation

Description of the Dose Modeling(continued)

0.295”

0.705”0.300” 0.208”0.197”

0.201”0.123”

0.042” 0.157”

0.039” x 0.039”

0.087”0.027”

0.027”

XY

XZ

Kovar lid: 0.455” x 0.274” x 0.010”

Top and side views(Kovar lid removed)

When in place, the lid is centered on the top of the device

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Discussion of the Results External and internal annual doses for solar maximum conditions1 in three

orbit types and a PCB with no (0-oz) ground plane

1.: Trends for solar minimum conditions are the same2 : 40-GSO-0Oz-Batt represents the 40-mil spacecraft in GSO having an electronics board that has no rear ground plane and located near the –X battery 3: An external location on the top of the spacecraft4: An internal location inside the Spacecraft next to the +Z,-Y corner of the electronics board 5. A location on the populated face of the electronics board, near the +Z,-Y corner of the electronics board

NOTE: The board’s populated side faces the +X direction, i.e. towards the center of the spacecraft.

CommentsThe additional shielding provided by the 135-mil spacecraft varies with the energy distributions of the electrons and protons within the orbit. It is a factor of approximately 30 for GSO, 15 for GTO, and 8 for SSO. The effect of the location in the spacecraft (at the negative-X axis’s battery or shear panel) on the dose is a complex consideration that depends on the exposure’s solid angle, exterior panel thickness, and adjacent interior components. The PCB (without a 4-Oz ground plane on its backside) reduces the dose by an additional factor of 2. Although this amount of dose reduction is not sufficient in most cases it does indicate that the board material and its sizing should be included as part of the dose modeling.

40-mil Spacecraft, rad(Si) 40-GSO-0oz-Batt2 40-GSO-0oz-Shear 40-GTO-0oz-Batt 40-GTO-0oz-Shear 40-SSO-0oz-Batt 40-SSO-0oz-Shear

OUTSIDE SPACECRAFT3 1.25E+09 1.25E+09 8.05E+09 8.05E+09 2.74E+05 2.78E+05

INSIDE SPACECRAFT4 9.18E+05 8.18E+05 1.93E+06 1.86E+06 1.08E+04 9.18E+03

ON SURFACE OF BOARD5 5.06E+05 2.09E+05 1.05E+06 5.45E+05 5.95E+03 3.24E+03

135-mil Spacecraft, rad(Si) 135-GSO-0oz-Batt 135-GSO-0oz-Shear 135-GTO-0oz-Batt 135-GTO-0oz-Shear 135-SSO-0oz-Batt 135-SSO-0oz-Shear

OUTSIDE SPACECRAFT 1.24E+09 1.24E+09 8.01E+09 8.01E+09 2.69E+05 2.69E+05

INSIDE SPACECRAFT 2.62E+04 2.86E+04 1.19E+05 1.25E+05 1.18E+03 1.35E+03

ON SURFACE OF BOARD 1.66E+04 1.22E+04 7.78E+04 5.22E+04 8.15E+02 7.90E+02

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Discussion of the Results(continued)

ON SURFACE OF BOARD, rad(Si)

40-GSO- 0oz–Batt

40-GSO-0oz-Shear

40-GSO-4oz-Batt

40-GSO-4oz-Shear

40-GTO-0oz-Batt

40-GTO-0oz-Shear

40-GTO-4oz-Batt

40-GTO-4oz-Shear

40-SSO-0oz-Batt

40-SSO-0oz-Shear

40-SSO-4oz-Batt

40-SSO-4oz-Shear

SOLAR MIN 5.05E+05 2.08E+05 5.20E+05 2.39E+05 7.57E+05 3.85E+05 7.65E+05 4.29E+05 2.80E+03 1.58E+03 2.50E+03 1.44E+03

SOLAR MAX 5.06E+05 2.09E+05 5.21E+05 2.40E+05 1.05E+06 5.45E+05 1.06E+06 6.15E+05 5.95E+03 3.24E+03 5.18E+03 2.90E+03

ON SURFACE OF BOARD, rad(Si)

135-GSO-0oz-Batt

135-GSO-0oz-Shear

135-GSO-4oz-Batt

135-GSO-4oz-Shear

135-GTO-0oz-Batt

135-GTO-0oz-Shear

135-GTO-4oz-Batt

135-GTO-4oz-Shear

135-SSO-0oz-Batt

135-SSO-0oz-Shear

135-SSO-4oz-Batt

135-SSO-4oz-Shear

SOLAR MIN 1.57E+04 1.12E+04 1.54E+04 9.48E+03 5.89E+04 3.92E+04 6.05E+04 3.91E+04 5.23E+02 5.02E+02 5.22E+02 4.78E+02

SOLAR MAX 1.66E+04 1.22E+04 1.63E+04 1.05E+04 7.78E+04 5.22E+04 7.98E+04 5.18E+04 8.15E+02 7.90E+02 8.13E+02 7.43E+02

Comments The dose reduction due to board location (outboard near the battery versus inboard near the shear panel) is larger for the 40-mil spacecraft and varies more with the orbit. Thus PCB’s contribution to the total shielding is more significant for smaller spacecraft. The additional shielding provided by the 4-Oz copper ground plane is not consequential for either the 40-mil or the 135-mil spacecraft.

Annual dose on the surface of the board, with and without a ground plane (1), for the two board locations (2), and the three orbits.

(1) – “0oz” means without ground plane and “4oz” means 4-oz ground plane(2) - “Batt” means located near the battery and “Shear” means near the shear panel

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Discussion of the Results(continued)

Dose reduction effects of plastic and ceramic encapsulation

Comments Dose modeling typically models the dose inside the spacecraft (bar 1) and doesn’t include device encapsulation For the 40-mil spacecraft, plastic encapsulation (bar 2) reduces the dose an additional order of magnitude in all 3 orbit types. The ceramic encapsulation (bar 3) reduces the dose 2 additional orders of magnitude, except for the SSO. For the 135-mil spacecraft, the plastic encapsulation (bar 2) reduces the dose by a factor of ~5 and the ceramic encapsulation (bar 3) reduce the dose an additional order of magnitude. The trends for the effects of encapsulation are also true for near the shear panel and for solar minimum conditions at both locations. (data not shown) The additional shielding provided by encapsulation may explain flight cases for which parts do not fail even though gamma radiation tests suggest the opposite.

Non-shielded Devices on 0-oz PCB in 40-mil Spacecraft Near Battery(solar maximum conditions)

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

Annu

al d

ose,

rad(

Si)

INSIDE SPACECRAFT Plastic- NoShield Ceramic w Lid - NoShield

GSO GTO SSO

Non-shielded Devices on 0-oz PCB in 135-mil Spacecraft Near Battery(solar maximum conditions)

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

Annu

al d

ose,

rad(

Si)

INSIDE SPACECRAFT Plastic- NoShield Ceramic w Lid - NoShield

GSO GTO SSO

40-mil Spacecraft 135-mil Spacecraft

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Discussion of the Results(continued)

Additional dose-reduction provided by PolyRAD1 for plastic encapsulated (packaged) die

Comments These data are for plastic encapsulated (packaged) die adjacent to the –X battery inside the 40-mil spacecraft. Conventional representation of the dose reduction provided by a supplemental shielding, as shown in the next slide, does not include the encapsulation material. The limit for dose reduction is achieved by a shield thickness of approximately 20 mils. This is 25% of the thickness indicated by conventional representations (see the next slide) and thus a significant weight savings.

1 – PolyRAD is an advanced radiation shielding material developed under a NASA SBIR contract

PolyRAD Shield Performance at Solar Max Conditions for Encapsulated Devices(at the battery location)

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

0 10 20 40

PolyRAD shield thickness

Annu

al D

ose

at th

e di

e, r

ad(S

i)

GSO GTO SSO

Dose in the spacecraft but outside the encapsulant

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Discussion of the Results(continued)

PolyRAD Shielding for Solar Max Conditions

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

1.E+10

1.E+11

0 20 40 60 80 100 120 140 160

PolyRAD shield thickness, mil

Annu

al d

ose,

rad(

Si)

GSOGTOSSO

PolyRAD Shielding + 40-mil Aluminum for Solar Max Conditions

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

0 20 40 60 80 100 120 140 160

PolyRAD shield thickness, mil

Annu

al d

ose,

rad

(Si)

GSO

GTO

SSO

Conventional methods for representations of the dose-reduction provided by PolyRAD1

Comments On the left: Just PolyRAD, thus the dose for zero thickness is that of bare (neat) space On the right: PolyRAD + 40-mil aluminum, thus the dose for zero thickness is that behind 40-mil aluminum. The limit for dose reduction requires from 80- to 160-mil thick PolyRAD. Thus conventional modeling may overestimate the amount of required supplemental shielding. This could be a error for small, weight-critical spacecraft.(Conventional modeling does not account for shielding provided by the spacecraft/internal component structure and the material type and size for electronic boxes, PCB, and die encapsulation.)

1 – PolyRAD is an advanced radiation shielding material developed under a NASA SBIR contractNo spacecraft 40-mil spacecraft

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Discussion of the Results(continued)

Dosimetry implications of encapsulation

Comments The ceramic-packaged die in this study is similar to a candidate radfet package for space flight dosimetry. The measured dose predicted by the modeling (kovar lid in place) is from 1 to 2 orders of magnitude less than on the board surface:

For 40-mil spacecraft – Modeled measured dose is from 1 to 8 percent of that at the board For 135-mil spacecraft – Modeled measured dose is from 1 to 4 percent of that on the board

Removal of the Kovar lid significantly reduces the dosimetry error.

Board near battery on 40-mil spacecraft, solar maximum conditions

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

Orbit

Annu

al d

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rad

(Si)

ON SURFACE OF BOARD

Ceramic with kovar lidCeramic without kovar lid

GSO GTO SSO

Board near battery on 135-mil spacecraft, solar maximum conditions

1.00E+02

1.00E+03

1.00E+04

1.00E+05

Orbit

Annu

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rad(

Si)

ON SURFACE OF BOARD

Ceramic with kovar lid

Ceramic without kovar lid

GSO GTO SSO

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Summary Remarks This study modeled the dose-at-the-die for an array of copied devices on a single

board at two locations in two different generic spacecraft designs (40-mil and 135-mil) for GSO, GTO, and SSO radiation environments.

Observations from the modeled doses: PCB (0.062”) reduced the dose approximately 50 % 4-oz Copper ground planes did not have a significant effect on the dose. For the 40-mil design the location of the board varied the dose as much as 50%. The combined effect of the spacecraft structure, internal adjacent components, the PCB and its location, and the device encapsulation reduced the dose two orders-of magnitude for GSO and GTO and a little more than one order-of-magnitude for the SSO.

The amount of supplemental shielding (in this study PolyRAD) to attain low doses using the detailed approach to modeling in this study is 25 % or less than that determined from conventional modeling. This indicates that significant savings in the mass cost of supplemental shielding are possible.

The effects of encapsulation material can introduce significant dosimetry errors for devices such as radfets.