Aerospace & Defense Technology - February 2022 - 29

RF & Microwave Technology
Using Open-Cavity Plastic Packages in Avionics Applications
S
emiconductor makers invest significant
resources in the development
and manufacture of their devices,
including packaging and assembly
techniques that accommodate their
material, mechanical, electrical, reliability,
and footprint specifications. They
must meet very tight time-to-market
windows as cost-effectively as possible.
Fast-turn prototype package assembly
is frequently employed for rapid IC
design verification. Open-cavity plastic
packages (OCPP) are an attractive quickturn
assembly option when commercial
off-the-shelf (COTS) prototype packages
are not available. QP Technologies can
convert any existing IC plastic packages,
whether dummies, electrical test rejects
or excess inventory, into open-cavity
packages, ready to be assembled with
new die. By converting a range of popular
package types, sizes and pin counts,
new packages can be created that will
fit an established footprint. This allows
them to be easily inserted into test sockets
and boards, so that no retooling or
redesign is required.
OCPP is also viable for production
package assembly. It becomes an attractive
option when there are no onshore
sources for the particular plastic package
assembly, and lead time and ITAR*
constraints prohibit offshore assembly.
When avionics ASIC provider Device
Engineering, Inc. (DEI) ran into this
problem, QP Technologies' OCPP
approach was an effective solution for
DEI's crucial production schedule, reliability
requirements, and ITAR supply
constraints.
OCPP vs. OmPP
QP Technologies' two key types of
package offerings are OCPP and its
patented Open-molded Plastic Package
(OmPP™) technology. What's the difference?
*
OCPP is analogous to a quality " preowned
car. " Using OCPP allows us to
reclaim existing " dummy " packages,
e.g., electrical rejects, test packages,
or excess inventory. After removing
all plastic and existing die, down to
the copper, a new package is then
built within the OCPP shell. OCPP
is well suited for cost-sensitive projects
or those that only require small
batches.
* OmPP is the " new car. " Using these
packages, we start with the bare leadframe
and copper, perform die attach,
then wire bond and overmold the
die, and then we singulate and trim
the device. Tested to RF frequencies of
40+GHz, OmPP is a proven, cost-effective
alternative to industry-standard
ceramic for most applications.
Another key application for OCPP
is to employ it as an interim solution,
optimizing the package and working
out any kinks, before transitioning to
OmPP.
DEI's Challenge
DEI turned to OCPP technology for
production assembly of a 64-lead TQFP
[thin quad flat pack] 10 × 10 mm ePad
product when its onshore assembly
provider ceased doing business. DEI
sourced suitable dummy (no die) IC
packages from an offshore supplier, and
QP Technologies converted them to
OCPP, developing the assembly process
and materials to achieve the required
package performance.
The IC was characterized for JEDEC
moisture sensitivity level (MSL), as
determined by J-STD-020, and qualified
via environmental stress-based accelerated
reliability tests. The IC was qualified
in the end product and has since
entered production.
QP Technologies' Methodology
To find the right process that would
meet DEI's specifications, QP Technologies
experimented to evaluate various
types of OCPP. First, 64-lead TQFP
packages were opened and sent out to
plating to protect the copper with a
nickel-gold (Ni+Au) alloy. Nickel acts as
a diffusion barrier, with gold protecting
the circuit from elements.
Various die-attach epoxies were then
evaluated. These included Ablebond
84-1lmi and H70E, both electrically
conductive epoxies with silver particles.
In both cases, epoxy bleed-out later
created delamination between encapsulation
and surface of the
package, with parts failing
solder stress tests as
detected by CSAM [scanning
acoustic microscopy]
imaging.
Next, another designof-experiment
sets (DOEs)
was started, working with
unplated OCPP packages.
Again, various epoxies
were evaluated, and
Ablebond QMI529HT was
determined the winner.
This newly formulated
epoxy is designed specifically
for copper, features
minimal bleed-out, and
Figure 1. Qualification test plan for 64QFP OCPP
Aerospace & Defense Technology, February 2022
www.aerodefensetech.com
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Aerospace & Defense Technology - February 2022

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