Techbriefs... Electronic Components and Circuit, Electronic Systems,... 02-03... National Aeronautics and Space Administration... March 2002

67 Pages·2002·14.8 MB·English

by  National Aeronautics and Space Administration

Nas =h ike Ofb3
Electronic Components and Circuits
Electronic Systems
Physical Sciences
Fa>rication Technology
Mathematics and li.t0. mation Sciences
TOOOOOFYDU! :
Life Sciences
02-03 POCA EAS FS © Gul Cc March 2002
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NASA Tech Briefs, March 2002

& TechBriefs
National Aeronautics and
Space Administration
Electronic Components and Circuits
11 Electronic Systems
19 Physical Sciences
31 Materials
41
47
51
2||O'#B0/ 0 0/6 9|0
61
ir
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{BILAN PAGE
Electronic Components and
Circuits
Hardware, Techniques, and Processes
7 Mounting Flip Chips on Heat-Dissipating, Matched-CTE Boards
8 Lightweight, Dimensionally Stable Printed-Wiring Boards
8 Nanoelectronic Devices With Precise Atomic-Scale Structures
Books and Reports
10 PCI Bridge to Instrandu Tmeleecomnmunticastio n Systems
b BLAN PAGE
Mounting Flip Chips on Heat-Dissipating, Matched-CTE Boards
John H. Glenn ResearCecnther ,
solder joints are less likely to fail. Cleveland, Ohio
“Fip chip on board (COB) with high
thermal conduacnd ttaiilorved icoetffiycie nt
of thermal expansion (CTE)” denotes a
Gevelocopncempt eforn reltativaelyl in ex-
pensive, ightweight packaging of electron-
ic croults to accommohgdh adetnsieti es
of compaond nof eintnercotnnecstion s.
The cor.cept addresses several issues thal
pertain to fp-chip performaandn rcekaet¥ -
ity and to the integration of fip chips with
other compoTnhesee nisstuess in:clu de
munsrof iundzesiared tmiismaotchnes of
CTEs between fip chips and printec-winng
boards (PWBs), removal of heat from high-
power fip chips, and the need to madmize
Usually, a conventPiWBo insa mlad e
of an epoxy-matro/giass-lfarimnbienarte ,
Called “FR-4," with copper surface lay-
ers that can be etched to form signal
and power conducAt PoWBr sof. th e
present developtmypee nintcluadels a
core layer that contains a carbon cloth,
sandbewtweien cFR-h4 oueter dlaye rs.
Typically, the thickness of the carbon-
Cloth layer is about one-third the overall
thicokf nthee lasminsaie .
Carbon doth is used in the core ayer
because ft has several properties that ae
Gesirable with respect to the issues men-
tioned above. There properties include the
high thermal conductivity of carbon
fibers (up to 1,100 Wim), low CTE
|<<10°* (Cy" in some cases], low mass
density |=0.07 bin? (1.9 kg/m) for carbon
versus =0.1 bin? (28 kg/m) for av
minum], and high stifiness jup to =42 Mpsi
(=290 GPa) for carbon versus =10 Mos
(~69 GPa) for atminum].
The uss < 3 carbon-cofrie blayeerr t o
increase the therma conductance of a
PWS and thus the ability of the PWB to dis-
sipate haat offers two benefits. One benefit
is higher refabity: t has been estimated
that in many cases, lowering the ternpera-
These Temperature Maps were computed in a finite-element simutation of thermal conditions on
ture of operation of electronic components
a PWB on which four heat-generating fip chips are mounted. For each of the two cases shown
by 10 °C approddnouablets ethle myea n
here, the peak temperature mentioned in the text was caicuéated as an average over all nodal
values within the “ootprints” of the flip chips.
fi chp was estimated to be «277 F PWB was found to be «2.1 x 10°5 °C)’.
(=136 °C) on a conventiFRo-n4 aPlWB Thus, the carbonc-oref eixhibbiets rle ss
but only «129 °F (<54 °C) on a carbon- CTE mismatch with the chip substrate
fiber-core PWB. material — silicon — for which the CTE
in one example in the CTE-mismatch ranges from 3 x 10° to 5 x 10°6 ¢Cy"’.
fiber-core FCOBs have shown the poter- analysis, the effective CTE of the region Ultrasonic imaofg caribon-nfibegr-co re
tial for matchingo f CTEs and lowenng of a carbon-fibweherre- cfiop rcheip s FCOB specafiter mtheermaln tescts of
Operating temperoaf ctomupornenetss. in would be mounted was foutnod b e the specreveraledn theat tnhe tsher mal
one @arnple m the temperataunarlyesi s = 1.0 x 10°° (C}"; in contrast, the cor- tests dij not result in any detectable
(see figure), the peak temperatuundreer a respCToE ofn a dconvientinonagl F R-4 increase in the incidence of faiures of
NASA Tech Bnefs, March 2002 7
fip-Chip-mosuolndteri jnomgt s inquines concneghitms fiortnheg co m- Altn: Steve Fedor Mai Slo4p-8 21000
Ths work was done by Gan Lee ax meraal use of ths nverton should be Brookpark Road Cevela Oho 44135
Willan E Devs of Anpled Maternal Tech addrto eNAS‘s Glsenne Redsea rch fete to LEW-16890
nologres, inc., for Glenn Research Cx:er Center, Commercaal Technology Office,
Lightweight, Dimensionally Stable Printed-Wiring Boards
in comparison with traditional PWBs, these offer John H. Glenn Research Center,
better heat dissiapnd aCTtE imaotchning . Cleveland, Ohio
ad te comporets feo. badess Cm
Camers) mounted on them. Prevous sobp
tons to the heat-cisasndp aCTtE oprno t
lens fheve moiced Te use of copper
inver/co(OpOp ecorre s. WhCIeC co res
contribute to reduced CTEs and noreased
thera conducttheuy tasio econstri,bu te
to Incr¢me wagaitss aend scos ts.
Carbon cloth is used in the core layers
of the present PWBs because @ affords a
Comboif prnopeartiets filow oCTEn. h igh
and hgh stifiness) that help io satisfy the
requirements mentioned above. [The use
of carbon cloth in the core layers of PWBs
for this reason is reported in the preceding
article, “Mounting Fip Chips on Heat-
Dissipating, Matched-CTE Boards” (LEW-
16890).| The present carbon-coPrWBes
Offer the advantbuta nogt ethes d,isa d-
vantages, of PWBs with CIC cores: that
is, unlike those with CIC cores, these are
This PWB Contains a Carbon-Cioth Core and a total of engi copper layers. The overall dimen-
sions of the board are approxim3.a25 tbey 4l2y5 in. (ab8.3o byu 10t.8 c m)
Printed-vwiing boards PWBs) tet ae plus inner cores thal cortan carbon Goth
especialy sudable as substrates for hghy rel- These PW2Ss are intended to accornmno-
abe, ightwagt d@ectonc croutts fo aca date wh densities of d@ectrornc compo-
and spacheavec berena defveltope d. Like nents and of interconneacmotnig otnhsan
vaditona PVs, these PVs are laminated The designs of these PWSs can be opb-
compthat oinclsude ciialatctnc einnesr la yers mized to satsly sevea requreme;nts.,
ps copper oute ayers that can be etched including removal of heal generated nm elec:
to form signal and power conductorGsa.ng tronic components, ma@enization of stiffness Center, Commercial Technology Office,
beyoy! the desgns of taditiond PVWGs, with minwnof wwazg, aantd omrwnriz a- Attn: Steve Fedor, Mail Stop 4-8, 21000
these PWSs node muffpie copper ayers ton of mismbeatweetn tche hcoefsicen ts Brookpark Road, Cleveland, Ohio 44135
separated by Gielectnc (e.g... polyrride) layers, of thermal epangon (CTEs) of the PWBs Retto LeEW-r166 48
Nanoelectronic Devices With Precise Atomic-Scale Structures
Field-effect transistors with nanometer dimensions are Ames Research Center,
under development. MofFfielde, Ctalitforn ia
Since its invention in 1948. the transistor hon of integratechidps- hcavre osiuzets o f below 0.1 umn — a thousandth of the wadih
has revolutionzed everyday life. The elec- «18 umn, and the eiectroncs industry has of a hurnahna r However, studies ncicate
trorecs revolution is based on mwatunza- completed development of O.13-urn tran- that the mwwaturof vsoaont tiranoasntor s
ton of transistors; snaler transistors ae sistors, woh wil enter productwointh n wil soon reach its knw
faster, and Genser crouitry has more func the next few yeas. ndusty researchers For further progress in microelectronics,
tonality Transn tihe sprteseont rgesner a- are now wortdng to reduce transistor sizes iti S Necessary to turn to nanotechnology
NASA Tech Bnets. March 2002
Rate flan cor@rury to rewire ra
seis © @ port wee fey becore
urvelabie, nanctactrOffoeris oheg yne w
approach of buliding devices on the aforn-
ic scale. One wsion for the ned generation
of mwwhre dectok Gosty & ta of
@tomic-chan @lectorics, according to fs
vigion, each devic:s is composed of alors
aged on top of a .istate astace na
regula pattem. The Atomic Chain Gec-
tonics Project (ACEP) — part of a nan
Cecnology goup @ Ames Reseach
Carter .— has been developing the theory
fo understanding alormic-chan devces.
ad 8 patert to aomc-chain e@actorics
has been Sed and is now pending.
The use of Goparts 6 clicd lo fe
tirctonaity of tarestors. Doparts we
mpuries merntadodedn tao tlhe ysar e
contadnsisiuo: Ccharreti to; rais e or
lower the device swic+-on voltage
Typically, @ macroscopic varsisio’ fore
wih a size of the order of 10° m contains
severa fousand dopant alors fal, on
the scale of the over device, apped to
be sneered ouf as a dopart “jelly,” as @us-
vated in the top part of Figure 1. Because
of the large nurrbe of dopart ators, the
Source
precise location of each dopart atom is
not very enportart to the tunctioning of the
vangistor. Howewhevn tehe rsiz,e of a
vanaistor is reduced to the range of 10°*
to 10°” m, as Gustated in the middie part
of gure 1, the nunibe of dopart atoms s
less fran about 100, n which case fe
Ato<m10°i mc (ta:p) (c)
of the few dopant atoms precisely, and as Figure | Transistors Heve Been Mintsartesd. startny form fhe macroscop scale. where Mou
a ream, ond vemos fm irctowg sands of dopat storns can be regarded as being © a encom deeingon Pet deternmes fhe
switt-on voRtage Al the mesoscope scate, anemstors hove Giterert sxitt+on volagss, depend
ocoy among tranaistors. Such variaiions
ig on precisaly where fhe dopart storms ave located To prevert such u-to-w veriafors, fhe
ae tata’ when miiors o blions of tarais-
Next step © murusturizeton w8 not be ecoomplished by matung comentora/ vansist-ys safer
tors we megated m a commuter Cw,
retesd. vaneiwish Gtreonsrorss <1 rym wi be made turn chams of preciesly posiiioned strns.
because the variations can cascade fom
one device to the next. evertualy gg not) appied — field effect. Metals aways atoms in air iti s necessary to place them
fee tf a marci A sohdioof nfi s conduct cvrert. A feki-eflect ranistor on top of a substrate. Surface atoms of
aspect of te minetvization protien, uses @ semicontodr tuhe cChtannoa ran d tte s.israte attract ators in the chan
devised by the ACEP és to cuate di te @ meta to d@ectanod dfse 6s h,ow & and hokd then at ted positions. The sur-
device structures wih aor Cwis ed actweves large gan. Thus, @ is necessary face of a substrate can be made to have
oul na reguéer precise pattern by anchor- to devee Chains wih semiconductasr d atc" *cale Corrugaatndu thnesse ,ca n
rg atoms to a sierate, as stated n meta properties. Fret, fe ACEP tean be used to creste ¢ precise pattern for
the botptarto ofr Fignure 1. tackéed @ senple protien theoretically ff @omic-chan d@ecturics. However, te
A second oftical aspect of the function one can arrange siicon atoms dong a re atractve toro, between the sisrate
ng Of a vanesto 6 gan te ag of te foating in a, is tis Chan sericoncact- and chain ators that ae srnply placed n
vangistor shouid be a magiied version of rng? The weve 6 superg Shag the corruigs iaco tweiak oton ssecv e
& rout. ACEP rosheasa iecd bh t e buk or twin silicon is sericoni.ctry, atorne reliably, ACE reseahars ctehd t o
condusion that n desigwng atomic-chain @n isolated chain of silicon atorns is aways the concthlat ua Chsemiicalo bonndi ng
vansitos ptrodoucre sga n, ore sou metalic. FortunACaEP treeselarcyh ,as o scheme is neede:! to secure Chain atorns
egicot te tek ofect, wih 6 Te ov letaf fde sfixi ng Tal 2 magnesium rehably, and to the turther conclusion that
mechveriiaed nepeiimenstalyn ©) tr Chain iss emiconduevcent tiounghg ,bu k the properties of a C.ain are strongy inf
a@t the atorric scale. Serra ochuctors o> magnesisi muetamli c enced by the substrate material and au-
@uct current only when a ode voRage is és Of course, @ is not possittoi feoa t face orienwhetn cahetmicial obonndi ng