1. THE METHOD OF MAKING LOW-COST MULTIPLE-ROW QFN
Mary Jean Ramos, Rico San Antonio, Lynn Guirit, Anang Subagio and Hadi Handoyo
Unisem Singapore Pte Ltd
1 Maritime Square, #09-80 HarbourFront Center
Singapore 099253
jramos@aitemail.com, rsantonio@aitemail.com, lguirit@aitemail.com, asubagio@aitemail.com and
hphandoyo@aitemail.com
Abstract
QFN demand has dramatically increased during the past 3
years. It has been replacing older packages like SOIC and
TSSOP mainly because of the added thermal enhancements
from the exposed pad, as well as the elimination of
coplanarity issues. QFN is also being chosen for next-
generation packages because it has a relatively bigger pad
size, allowing more flexibility in accommodating bigger die
size, die integration and the added advantage of thermal
enhancement. However, as the package requires more I/O in a
smaller footprint, current QFN structure will have some
limitations. Currently, there is a solution for two rows of I/O
but any higher than that, the available solution becomes more
expensive – one solution requires laser cutting to isolate each
row and another requires use of photo-imaging, develop and
etching process to define the I/O.
This paper describes an alternative methodology for
making a low-cost QFN with multiple rows. The leadframe
raw material that will be used will be solid copper, half etched
on one side, with selective silver plating. The difference from
existing QFN leadframes is that this does not need tape during
molding.
There will be two new processes introduced: selective
copper etching and electroless plating. Although these
processes are commonly used in other industries, the
challenges and proposed solutions encountered in adopting
them in IC packaging assembly will be discussed.
Apart from the cost advantage, manufacturing and
performance advantages and disadvantages related to these
new methods will also be tackled.
Keywords: multiple-row QFN, Cu etching, electroless/
immersion plating.
Introduction
Leadframe-based packaging is a low-cost IC solution.
However, conventional leadframe proves to have limitation in
the ever increasing complexity of the product. Moving to a
substrate-based solution is inevitable since it offers a lot of
flexibility through routing and multi-layer metal construction.
However, the drive for a low-cost solution is still commonly
preferred. Multiple-row QFN has brought the package to
another step of satisfying the increase in I/O. The inner leads
could be produced by using a narrow tie bar attached to the
connecting bar that is holding the outer leads (refer to Figure
1, Type A). The inner leads are very challenging to make and
the narrow tie bar lacks rigidity, making the wire bonding
process more difficult. This results in lower productivity and
yield. On the other hand, dual-row QFN can also be produced
by having the inner leads connected to the die pad (refer to
Figure 1, Type B). This is more robust, but it requires a two-
pass sawing process, whereby the first pass is using partial cut
to isolate the inner lead from the die pad and the second pass
is the final cut to singulate the units. Due to this two-pass
process, the saw capacity is reduced 50 percent and is likely
to produce rejects (i.e., burr, smear and metal shorting). Refer
to
Figure 1 to illustrate the two designs. Type A illustrates the
former method and Type B illustrates the latter method.
With the current challenges on the existing dual-row
QFN, a new multi-row leadless packaging was developed to
offer not only dual-row but also higher I/O low-cost
packaging with the advantage of better wirebond stability
with patronizing standard manufacturing processes such as
the single pass sawing process.
This paper will discuss in detail the methodology and
construction of etched leadless package (ELP) as the new
alternative multi-row packaging.
Type A Type B
Figure 1. Dual-row QFN options. In Type A, the inner leads are attached to
the same connecting bar that holds the outer leads. In Type B, the inner leads
are connected to the die pad.
Comparison Between Multi-row QFN and ELP
Leadframe Design and Bondability
A standard multi-row QFN utilizes the conventional
leadframe-making process: the majority of the leads and
features are created by etching through the top and bottom of
a copper stock, which is about 0.20mm thick. For Type A
multi-row QFN, the inner leads are attached to a half-etched
connecting bar. This makes the structure weak and prone to
bent leads.
A common problem for a typical QFN with tape is the
stability during the second bond formation. The use of Type
Die Pad
Connecting bar

2. A QFN makes this even more difficult due to longer lead
lengths and thinner connecting bars.
Dual-row Type B QFN provides better stability of the
leads during wirebond since the inner leads are shorter and
connected to a more rigid structure (i.e., connecting bar and
die pad). However, this solution requires a dual-pass package
saw singulation process that results not only in low yield and
productivity, but also in design limitations such as a smaller
die pad and a smaller number of leads to allow path for a saw
blade during inner cutting. Currently, both solutions, Type A
and Type B, allow for a maximum of two rows of leads only.
ELP is a multi-row leadless package that utilizes a
partially etched leadframe. The top portion is half-etched
which defines the desired features such as leads, power,
ground rings and die pad. The bottom portion of the
leadframe is solid. Due to the rigidity of the leadframe,
multiple heavy wire bonding such as 2mil Au wire, aluminum
wedge/ribbon bonding and copper wire bonding, are viable.
Figure 2 illustrates examples of design flexibility for ELP.
Figure 2. (A) Wire-bonded multi-row. (B) Isolated power and ground rings.
(C) Flip-chip (1. Peripheral, 2. Array). (D) Multi-chip module/system in
package.
Thermal Performance
The thermal performances of QFN and ELP are
comparable because they have similar features. Refer to
figure 3 for a theta ja comparison between QFN and ELP.
THERMAL PERFORMANCE
Figure 3 Thermal dissipation comparison between QFN and ELP.
Post Mold Cleaning
Typical QFN comes with tape underneath to prevent mold
flash. Depending on the tape used, this will require an
additional cleaning process after mold to remove the tape
residue and mold flash. Current cleaning methods available
are laser cleaning, chemical deflashing and mechanical
buffing. These additional processes and the tape required add
to the cost of the overall package by as much as 15 percent.
ELP has a big advantage in this area because it does not
require tape, therefore no extra cleaning is required and the
tape cost is eliminated.
Package Saw Singulation
Package saw singulation for a QFN requires metal cutting
between units. The metal thickness can range from full to half
the copper leadframe thickness.
There are several issues associated with this. First is low
productivity: Saw speed is typical at the range of 35-
60mm/sec, which is very slow compared to a standard punch
singulation process. Second is high blade consumption due to
metal cutting. Third is unavoidable cosmetic concerns such as
copper burrs and smear.
ELP undergoes back-etching process after mold. At this
stage, the copper in between units is fully etched out, leaving
only 100 percent mold compound left for sawing. This results
in an improved saw speed up to 120mm/sec, longer blade life
and absolutely burr-free units.
Refer to Table 1 for a summary comparison of multi-row
QFN and ELP.
Multi-Row QFN
Features
A B
ELP
Leadframe Full etched Full etched Partial etched
Taping Yes Yes No
Number of Rows 2 2 3
Pwr & Grd Rings No No Yes
Back Etching No No Yes
Standoff No No Yes
Plating SnPd / Sn SnPb / Sn Immersion Sn
Plate Thickness 7.6µm-20µm 7.6µm-20µm 1µm MIN
Saw Singulation 1 pass 2 pass 1 pass
Metal Cutting Yes Yes No
Typical Cut Speed 35-60 mm/s 35-60 mm/s >120 mm/s
Table 1. Basic comparison between multi-row QFN and ELP.
ELP Process Flow
Generally, ELP has similar processes and applicable
controls as an existing QFN package except for the etching
process and immersion plating process needed to isolate and
plate the leads respectively. For QFN, the isolation is done by
either sawing or punching. Figure 4 shows the typical ELP
process flow.
(A) (B)
(C)1 (C)2
(D)
(A) (B)
(C)1 (C)2
(D)
0
5
10
15
2 0
2 5
3 0
0.0 0.5 1.0 1.5 2.0
Velocity (m/s)
Theta-Ja(deg.C/W)
ELP DP soldered to PCB VQFN DP soldered to PCB

3. Figure 4. ELP process flow.
Backside Etching
In backside etching, the features are pre-defined by a pre-
plated mask. The process of masking can be done during
leadframe assembly or after the mold assembly process. Since
masking is an established process in leadframe assembly, it is
preferred to perform the masking during leadframe
preparation for process simplification and better control such
as placement accuracy.
The mask is either NiPdAu or Ag and can be the same
material plating used on the leadframe bonding side. Ag
masking is used because it employs straightforward stripping
before final plating. For NiPdAu, the stripping process is very
complex and costly due to the multiple stripping processes
needed (i.e., separately stripping Ni, Pd and Au). For this
reason, Ag masking is selected, as the process is simple and
takes only one stripping procedure.
To isolate the leads, rings and pads, the leadframe material
needs to be back-etched. This is done after the mold process.
After etching the backside to define the features, it is optional
to leave the Ag mask as a final finish. However, the Ag mask
will have overhang after etching. Since the mask is very thin,
it will tend to deform at any direction, which is cosmetically
unacceptable. Stripping off the Ag mask and re-plating it with
the desired finish is suggested.
There are two industry standards available for copper
etching: acid-based and alkaline-based. So far, there is no
known process that uses Ag as a mask. In selecting the
etching process, it is important to understand the chemical’s
effect on the Ag mask.
Ferric chloride and cupric chloride are the most commonly
used acid-based copper etchants, and ammonium chloride is
used as an alkaline-based copper etchant. Based on the study,
both chemistries were able to etch the copper, but acid-based
etchants easily attacked the Ag mask. After etching, the Ag
mask turned a dull color and was difficult to strip off.
Ammonium chloride slowly etches the Ag when exposed
to it for more than 1 minute. The etch time can speed up by
increasing the temperature to about 55 degrees Celsius to
make the chemical more aggressive. However, it shortens the
life of the bath due to the high loss of ammonia that results in
inconsistent etching. Increasing the pH will also increase the
etching rate of the chemical. This eliminates the Ag attack
and can operate at a lower etching temperature which
stabilizes the chemical. Another observation is that
ammonium chloride does not affect the Ag mask and thereby
enables the Ag stripping process. For reference, a starter
makeup has 8.2-8.6 pH. The pH can be adjusted by the
supplier and is maintained by adding ammonia liquid or gas
during the process.
Further evaluation was done to fine-tune the process using
alkaline-based etchant. There are two challenges: etching
consistency and attack on the Ag mask. Etching consistency
is defined as the etching rate uniformity on every strip
processed, which can be measured. The attack on Ag mask is
a visual criterion evident in the surface of the pad. Once the
Ag mask is attacked, the texture of the copper will be rough
or, in the worst case, etched. Refer to Figure 5.
Figure 5. Attack on the Ag mask.
There are four components in the alkaline etchant that
may affect etching consistency and Ag mask attack. These are
pH, copper content, temperature and chloride content. A
process guideline study for alkaline etching was used as
reference for the alkaline etching optimization.2
It was
determined that all of these factors must be analyzed and
controlled in order to find the fastest etch rate and the least
amount of undercut. The pH is a measure of the relative
amount of free ammonia (NH3) that is available to the etching
process. The lower the pH, the less the undercut. However, in
order to not attack the Ag mask, there is a need to bring up
the pH. On the other hand, if the copper content increases, the
amount of undercut decreases. Therefore, to compensate for
the high pH effect on undercut, the copper content must be
increased. The recommended range is between 140~165
gm/liter Cu. The chloride concentration indicates the amount
of ammonium chloride (NH4Cl) present in the system. As the
chloride concentration increases, more copper metal can be
held in the solution, allowing a decrease in the amount of
undercut. The chloride component also acts as a buffering
agent in the etchant, permitting a narrow pH window. The
etch rate will increase with the increasing bath temperature,
but so will the undercut. The best compromise between etch
rate and minimum undercut exists when the alkaline etch
baths are run at temperatures between 43~48 degrees Celsius
with 55 degrees Celsius as a maximum. Lower temperature
drives off less ammonia, making control of pH much easier. A
good balance between these four main factors must be
maintained to obtain the best and consistent etching. Table 2

4. below summarizes the effects of these four factors and the
recommended controls.
Further experimentation has been conducted to confirm
the impact on etching speed and time to the etching quality.
In the experiment, it was noted that lower speed increases
etching rate due to an increased in etching dwell time. For a
higher temperature setting, etching dwell time can be set
shorter. while longer dwell time is needed if lower
temperature setting is used.
Main Factors Process Effect Test Method
Control
Method
Copper
Concentration
Affects etch speed
Too high = risk of
precipitation
Too low = slow etch
Titration
(e.g., with
thiosulfate,
weekly)
SG controller
High = dump
Low =
dissolve
copper salt
Chloride
Concentration
Use to hold copper in
the solution
Too high = solubility
limit
Too low = slow etch
Titration
(e.g., silver
nitrate,
weekly)
High = dilute
with
concentrated
ammonia
Low = add
ammonium
chloride
pH Free ammonia is
needed to complex and
keep cuprous and
cupric salts in solution
Too high = lowers
etching rate due to
copper dilution
Too low = attack on
silver mask
pH meter
(handheld,
daily)
High =
evaporate
Low = add
aqueous
ammonia or
ammonia gas
Temperature Affect etch rate
High = higher etch rate
but rapid loss of
ammonia to ventilation
Low = low etch rate
Thermometer
(weekly)
Heater/cooler
on/off; adjust
set point
Table 2. Effects of etching factors and recommended controls.
Electroless/Immersion Plating
After backside etching, surface finishing is applied on the
isolated circuitry to prepare the material for board mounting.
While the leads and pads are already isolated, conventional
electrolytic process is not applicable and
electroless/immersion process is the suitable process. There
are two designs in the market: horizontal and vertical
immersion plating processes. The difference between the two
is that for horizontal process, the material is fed through a
conveyor, while for vertical, racks or trays are used to carry
the materials and dip them from station to station. Immersion
or electroless process is a longer process compared to
electrolytic. To achieve the plating thickness required for
electroless/immersion plating, the materials must be
submerged in the chemical for a long period of time. This is
where the decision must be made to either go vertical or
horizontal. If there is a space constraint, the vertical process is
recommended since a horizontal process could be as long as
40 meters. If there is no space limit and the capacity
requirement is high, the horizontal process is the best choice.
Both processes should have similar output in terms of quality.
In this paper, the process used was vertical
There are many immersion processes that can be used for
ELP: electroless Ni and immersion Au (ENIG), immersion tin
(ISn), organic solderability preservatives (OSP) and
immersion Ag (IAg). Each has its pros and cons. Refer to
Table 3 for a basic comparison.
Factors ENIG ISn IAg OSP
Solder Joint Ni-Sn Cu-Sn Cu-Sn Cu-Sn
Plating
Thickness
Ni 3-6 µm
Au ~ 0.08 µm
>1 µm
>0.127
µm
0.01 µm
Contact E-test E-test E-test No
Whisker No Yes No No
Shelf Life 24 mo 6 mo 12 mo 6 mo
Cost $$$$ $$$ $$$ $
Table 3. A basic comparison of electroless/immersion plating chemistries in
the market.
ENIG is a very stable plating solution. However, the cost
is high and the process control is challenging since there are
two metal components involved, nickel and gold. Also, waste
treatment must be considered due to the cyanide component
of Au. OSP is the cheapest solution but there is concern of
visual in-process control since it is colorless. There is also a
concern for electrical testing since it is non-conductive.
Immersion Ag is a cheaper solution than ENIG. The plating
time is very quick and low-temperature with plating thickness
only above 0.127 µm. However, IAg is very sensitive to the
environment and is easily tarnished. Good material handling
and environment control must be employed. Immersion Sn is
comparable in cost to immersion Ag. The thickness of ISn is
also relatively thin but doesn’t easily tarnish compared to
IAg. In IPC -4554 section 3.2.1, the immersion Sn thickness
shall be 1 µm minimum at 4 sigma. To achieve ISn thickness,
the plating process must be extended. Typically, it requires
about 30 minutes dwell at 70 degrees Celsius in the main
plating chemistry. This will define the length of the plating
system.
The plating thickness of ISn being only over 1 µm may
affect solderability due to quick intermetallic growth. It is
then suggested to have a 6-month shelf life to ensure
solderability. There is also a question on whisker growth
common to Sn plated products. ELP is considered as leadless
package and is exempted from the whisker growth category
based on JEDEC JESD201, as the leads will be fully covered
by solder during board mounting. However, the chemistry
selected has a whisker-limiting agent.
Studies on the kinetics of whisker growth state that
whisker is produced by compressive stress coming from the
buildup of Cu-Sn IMC during storage.3
This stress is relieved
by diffusion of Sn atoms resulting in whisker growth. This
whisker can occur along the Sn grain boundaries or near
lattice defects (see Figure 6).

5. Figure 6. Whisker growth along the Sn grain boundaries and near lattice
defects.
Whisker can be controlled by thermal excursion or what is
commonly called baking. This process increases the
oscillation of atoms within a crystal and at the same time
heals the lattice defects. However, since ISn is very thin,
thermal excursion or baking is not ideal since the temperature
will speed up the IMC growth that affects solderability. With
this as limitation, change in the chemistry must be made. The
chemical identified for ELP has a proprietary additive that
changes the Sn crystal structure to control diffusion. The
additive blocks the pathway along the grain boundaries and
heals the lattice defect, thus preventing whisker growth. With
solderability still a question due to the thickness, the
chemistry process requires pre-plating of a dense Sn layer
prior to final plating. This was done at a low temperature of
about 25 degrees Celsius. The purpose of this pre-plating is to
minimize IMC growth, ensuring better solderability after long
storage and multiple reflow processes. Refer to Table 4 for
information from the whisker growth study.
7-months Data Collection
Test Chemistry
26.04 06.05 17.05 31.05 09.07 07.09 22.11
Standard 0 4 7 7 9 9 9Ambi-
ent
temp. Additive 0 0 0 0 0 0 0
Standard 0 1 1 1 1 1 12X
Reflow Additive 0 0 0 0 0 0 0
Table 4. Whisker growth study. Rating @ 100x, where, 0=0,
1=<10µm/<5pcs, 4=<50µm/<5pcs, 7=>50µm/<5pcs, 9=>50µm/>10pcs.
ELP Package Construction
The etching process makes ELP construction different, as
shown in Figure 7. Since the leadframe is half-etched at the
beginning, a conventional locking feature is not applicable,
such as “lip” on lead tips and pad edges. A different approach
can be applied, such as slots on pad and irregular lead shapes
and profiles. Also, the external leads will be tapered as a
result of the etching process. The lead will have higher
standoff to about 2-4 mils (50-100µm). Refer to Figure 8 for
an ELP and QFN lead comparison. This feature will have
stronger soldering to the PCB and at the same time will
provide helpful space for flux cleaning when required.
Since the lead has a narrow tip compared to conventional
QFN and has more leads, test socket manufacturers need to
design good and reliable contacts. Several suppliers have
reviewed the design requirement and suggested that it can use
conventional socket design. So far, two sockets were tested
using 228L 12x12 ELP with triple-row, 0.5mm pitch. The test
insertion is only one pass with 100 percent yield.
Figure 7. ELP package construction.
Figure 8. ELP and QFN lead comparison.
Second-level reliability studies were performed to define
the limitations of the new lead design. These were done at an
independent lab in Hong Kong. The tests included package
pull test, mechanical drop test, mechanical bending test and
temperature cycling test. Refer to Table 5 for test references
and conditions.
Test Reference Testing Condition
Failure
Criteria
Mechanical
Drop Test
JESD22-B111
Condition B
g-level: 1500g
Duration: 0.5 ms
20% resistance
increase
Mechanical
Bending
Test
IPC/JEDEC-9702
Load Span: 70 mm
Support Span: 90 mm
Strain Rate: 5000 micro-
strain/s
20% resistance
increase
TC JESD22-A104-C
Condition G
Max. Temp: 125oC
Min. Temp: -40oC
Ramp Time: 15 mins
Dwell Time: 15 mins
> 10 kΩ
(not specified in
the standard)
Table 5. Second-level reliability reference.
The package pull test was done in comparison with 10x10
72L QFN package. To have one-on-one comparison, only the
outer leads of ELP were soldered to the PCB and both die
pads were unsoldered. The resulting pull forces were very
close to each other, with ELP showing two failure modes
(lead and pad). Lead failure mode is observed when the pull
force is <150N. Therefore, ELP lead pull strength is
comparable with QFN. Refer to Figure 9 for a package pull
data comparison between 10x10 QFN and 10x10 ELP.
Remarks:
1: Overall package
2: Leadframe
3: Die attach epoxy
4: IC die
5: Gold wire
6: Mold compound
7: External leads/
pad profile
8: Plating/surface
finish
1
6
54
3
2
87
HALF-ETCHED
QFN QFN
ELP
FULL LEAD ELP

6. Figure 9. ELP vs. QFN package pull data.
In the mechanical drop test, a high-speed oscilloscope was
used to monitor the daisy chain resistance in real time. The
oscilloscope can only measure voltage, not resistance.
Therefore, an extra bridge box setup is needed. The voltage
across the 100-ohm resistor was measured. If the package
failed during the drop test, the resistance of the daisy chain
would increase and the voltage across the resistor would drop
to zero. The units passed the mechanical drop test since no
failures were observed on all samples after dropping each
PCB up to 30 times. Refer to Figure 10 for the mechanical
drop test setup and results.
Figure 10. Mechanical drop test setup and results.
In the mechanical bending test, the crosshead speed was
2.54 mm/s. A strain gauge was installed in the middle of the
PCB to monitor the load, displacement and strain reading in
real time. The samples passed the mechanical bending test
since no failure was observed in all the test boards. Refer to
Figure 11 for the mechanical bending test setup and results.
Figure11. Mechanical bending test setup and results.
In the temperature cycle test, each unit in the board was
monitored in real time inside the chamber. The ELP samples
tested has reached >1,300 cycles @ -45/+125 degrees Celsius
without any failure and was still an ongoing test. Refer to
Figure 12 for temperature cycle test setup.
Based on board-level reliability design studies, an 8x8
QFN package was able to reach 1,126~1,356 cycles in
-45/+125 degrees Celsius conditions.4
Table 6 shows that
ELP performance is comparable with QFN package.
Figure 12. Temperature cycle test setup.
140N 150N 156N 270N
QFN
ELP
136N 230NQFN (Break @ Pad)
ELP (Break @ Pad)ELP (Lead Failure)140N 150N 156N 270N
QFN
ELP
136N 230NQFN (Break @ Pad)
ELP (Break @ Pad)ELP (Lead Failure)
-40
-20
0
20
40
60
80
100
120
140
0 20 40 60 80 100 120 140 160 180
Time (min)
Temperature(C)
Temperature Profile

7. Table 6. QFN lifecycle reference.
Package Reliability
Internal features such as pad and lead designs promote
interlocking with the mold compound and contribute to
package integrity during reliability tests.
The ELP internal feature design is different from the QFN
internal feature design, but it offers the same interlocking
strength as shown in its reliability test results in Table 7.
QFN interlocking has defined corners and extended lead
lengths while the ELP interlocking is on the curved half-
etched portion of multiple leads.
MSL 2
@260C
TCT
-65C/150C
500 cycles
Autoclave
121C, 15 PSIG,
168hrs
HTST
150C
1000hrs
Lot 1 0/77 0/77 0/77
Lot 2 0/77 0/77 0/77
Lot 3 0/77 0/77 0/77
Table 7. Reliability results on 68L 6x6, 2row ELP @ MSL2 and 260C IRR.
Assembly Challenges
As the construction of ELP limits routing of bond post, it
is expected to have long wire lengths, especially for triple-
row applications. The die sizes are typically small with fine
pitch bond pads requiring small bonding wire diameter. This
impacts the wirebond and molding capability.
Wirebond Process
The wire length is increased by 30-50 percent and requires
multi-row bonding. Standard loop or square loop type for
QFN is practically not adequate for ELP, as the latter package
requires good vertical clearance between different loop tiers
and extra kinks to support the longer wire lengths. It is
therefore recommended to use a loop profile capable for >3
kinks for better loop stability. Refer to Figure 13 for an
optimized multi-tier looping profile evaluated on two
wirebond platforms.
W/B Platform A W/B Platform B
Figure 13. Looping profile from two wirebond platforms using 0.9mil Au wire
diameter with 160 mils span.
Mold Process
With complexity in wire layout, it is necessary to
determine wire sweep performance after mold. Parameter
optimization was conducted to get the best mold response to
eliminate risks of wire short and wire sagging. Also, a new
mold compound type was considered to ensure robustness in
the molding process.
The property of this new mold compound is such that it
puts less pressure on the wires during the mold transfer
process. It has lower narrow gap flow pressure (NGFP) that is
most suitable for longer wires with multiple wire loop tiers.
As shown in Figure 14, the new molding compound shows
better wire sweep response than the standard mold compound.
0
1
2
3
4
5
6
7
8
9
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Wiresweep
Standard New
Figure 14. Wire sweep response between standard and new mold compound.
Conclusions
ELP is a solution to bring leadframe-based packaging
closer to substrate-based packaging. It offers flexibility that a
standard leadframe package cannot support such as heavy
wire bonding, split pad, SIP, etc. Its design improves yield by
eliminating known issues at assembly such as second bond
stability, mold flash and tape residue, all of which has a direct
impact to packaging cost.
Though the ELP package-locking feature is different from
QFN conventional locking design, the package- and board-
level reliability test results are comparable.
ELP introduces new processes that need to be considered,
such as back-etching and immersion plating. Back-etching
uses alkaline-based chemistry and plating uses immersion
type. These processes are not new but were used in different
industries. It is shown that with fine-tuning, these processes
will be able to support ELP requirements.
With the limitation of routing and with the higher I/O
design, the wire length will be longer and bring challenges to
wirebond and molding capability. It is needed to optimize the
looping parameter and mold parameter to ensure good wire
clearance. Using a low-pressure mold compound also helps
improve the manufacturability of ELP.
The simplicity of the process and the advantages at saw
singulation and mold processes makes ELP the best available
alternative solution for low-cost multiple-row leadless
packaging.

8. Acknowledgements
The authors would like to thank Wei-Leong Lee of
Atotech for support in the ISn evaluations, Sharon Loh of
MacDermid for support in the etching evaluations, Lowel
Begonia of KNS for W/B evaluation support, Raymond Koh
and CS Lim of ASM also for W/B evaluation support,
Benedict Yuen of ASM for support in mold evaluation, and
Clarence Loh and Chen Ping of Sumitomo for support in
mold evaluation. The authors would like to thank AIT’s QA-
FA team, Denny Muharyadi and Tanti Rahayu for the SEM
and DECAP support.
References
1. ELP patent, U.S. patent Nos. 6,777,265, 6,812,552 and
7,129,116
2. Chemcut, “Process Guidelines for Alkaline Etching”
(Technical Report for Alkaline Etching)
3. Atotech Deutschland GmbH, Sven Lamprecnht, Carl
Hutchinson, “Immersion Tin - Kinetics of Whisker
Growth” (technical paper for whisker-free ISn plating)
4. Advanced Packaging PennWell with title “Board Level
Reliability Design by Tong Yang Tee,” reference for QFN
board-level reliability
5. JEDEC MO-239, “Thermally Enhanced Plastic Very
Thick, Quad Flat No Lead Package,” reference for dual-
row QFN
6. IPC -4554 section 3.2.1, reference for minimum thickness
requirement for ISn
7. JEDEC JESD201 section 1 scope stating QFN type
package is excepted to whisker growth criteria