Study of Die Bond on Rou

Raymond Solis CAriel

In168 Kallan

Abstract This paper studies the challenges and beh

material between the silicon (Si) material aNi/Pd/Au-Ag alloy-plated Copper (Cu) leadfraµPPF) with anti-epoxy bleed-out (EBO) duprocess. Die bond on die attach paddle (DAPµPPF using Silver (Ag)-based epoxy has been its manufacturability in terms of maintaining thfillet height for a 300 µm Si chip thickness. Throughened µPPF utilizing die bond parameterepoxy on standard Ag-plated DAP Cu leadframheight greater than the maximum target limit thickness and reaching as high as 100% filleoccurrence leads to risks of epoxy componentthe chip surface which is detrimental (delamination on die top) and can cause manuloss due to die contamination and non-stick oduring wire bonding. The processability of thesurface of the roughened µPPF leadframeestablished due to this significant difference result when compared to the Ag-plated Cu lehas a major impact in the quality of the chip development of the die bond process for the rois separated into two assessments, namely escale assessment and die bond parametexperiment (DoE). The epoxy dispense scastudies the optimum epoxy glue coverage with area that will ensure a consistent epoxy voluthe Si chip (bond line thickness or BLT) anlinear epoxy fillet height formation along the sidchip. Once the optimum dispense scale is eDoE, the critical die bond parameters identifwindow where a controlled fillet height is obany impact on the functionality test responseThe study shows that a high epoxy dispenoptimum die bond parameter, namely, compondistance and dispensing height are required optimum epoxy fillet height control along the sSi chip.

1. INTRODUCTION The introduction of roughened Ni/Pd

preplated copper leadframe (known as µPPF) epoxy bleed out (EBO) as an alternative to plated Cu leadframes has been gaining grounalternative for usual Ag-plated Cu frames due treasons. First, legislative requirements are bewith regard to the safety disposal of hazard

ughened NiPdAu-Ag Pre-Plated Frame with An

Cabral*, Joseph Aaron Mesa Baquiran, Wu-Hu Li,Lizaba Miranda, Mary Grace Mercado

nfineon Technologies Asia Pacific Pte Ltd, ng Way, Singapore 349253, Republic of Singapore

* Corresponding Author

havior of epoxy and roughened ame (known as

uring die bond P) of roughened

a challenge for he target epoxy he study on the rs for Ag-based me yielded fillet

of 75% of die et height. This t creeping onto on reliability

ufacturing yield on pad (NSOP) e epoxy on the e needs to be in fillet height

eadframe which assembly. The

oughened µPPF epoxy dispense ter design of ale assessment respect to chip me underneath

nd achieving a dewall of the Si established via fy a parameter

bserved without e of the epoxy. nse scale and

nent over travel to achieve an

side wall of the

d/Au-Ag alloy [1] with anti-the usual Ag-

nd as a reliable to the following ecoming stricter dous chemicals.

Primary concern is the impact ofhazardous materials leaching into contaminating the water supply overtiand marketing forces are driving theremove certain hazardous materials fSecondly, µPPF is a good alternmechanical as well electrical propertiproperties of Pb in terms of packagingthe utilization of the leadframe on bacprovides shorter lead time as solder plfinal lead finish, is eliminated. The ecoating process saves investment on mand reduces the assembly cost of prparts.

Roughened µPPF with anti-EBOduring die bond process using Ag-badie thickness as manufacturability hFillet height of Ag-based epoxy onsurface proves to be a challenge to ctarget of maximum 75% of die thevaluations performed at die bond prthe samples having fillet height forma100% DT (Figure 1(a)). Attemptvolume, to compensate for the highinsufficient epoxy coverage at the chip

(a) Figure 1 (a) High epoxy fillet height reachi(b) Insufficient epoxy coverage at the chip corne

The occurrence of high fillet heigh

it causes the following problems fepoxy component bleed out creepingchip causes die surface contamination visual inspection screening as ma(Figure 2(a)). The surface contaminaStick on Pad (NSOP) once it reachearea intended for wire bonding. Delamalso a potential risk in the reliabildevice (Figure 2(b)).

nti-EBO

,

f lead (Pb) and other the groundwater and

ime. As such, legislative e electronics industry to from their products [2]. native as its thermal, ies are equivalent to the g requirements. Finally, ck-end assembly process lating process, which is a elimination of the solder

machine and maintenance roducing semiconductor

O has been a challenge ased epoxy on a 300µm has been a concern [3]. n this roughened µPPF consistently achieve the hickness (DT). Initial rocess show majority of ation of >75% DT up to ts to reduce the epoxy h fillet height, result in p corners (Figure 1(b)).

(b) ing 100% die thickness (DT) ers.

ht is very detrimental as for back-end assembly: g up onto the top of the

which is rejected during anufacturing yield loss ation will result in Non-es the critical metalized mination on top of die is ity performance of the

341978-1-4799-2834-7/13/$31.00 c©2013 IEEE

(a) (b)

Figure 2 High epoxy fillet height impact on assemblcontamination, (b) Delamination on top of die.

2.0 METHODOLOGY 2.1 Materials, Inspection Methods and Surface

The roughened µPPF leadframes used in thfrom one leadframe supplier. The base mleadframe is a piece of Cu sheet with a thickneA first full layer of Ni with a thickness oelectroplated on the Cu surface and a second fwith a thickness of ~ 12 nm is electroplated surface. A third full layer of Au-Ag alloy with~ 25 nm is electroplated on the second Pd topside of the leadframe is roughened to improvbetween the leadframe and the moulding compsolution of anti-epoxy bleed out (EBO) is asurface to control the resins of epoxy bleed [4].

Scanning electron microscopy (SEM) is usthe surface morphology of the leadframes. morphology of the roughened µPPF directbehaviour of the dispensed epoxy glue particuplacement of the singulated Si chip during thprocess. Measured results are compared to theleadframe, with plating thickness of ~ 5umdesign and supplier using the epoxy fillet heigresponse and target at maximum 75% of the Fillet height is measured using 50x magnificatepoxy curing process. Prior measurement, samples are cut horizontally to stand perpenscope eyepiece using a handling support. subtraction method is then used to determine theight ratio with respect to chip thickness.

To prevent process and material variationconducted at the same manufacturing time, equbatch and process parameters. Although an adjvision camera setting is necessary for both leathe roughened µPPF appears to have a darker the vision camera in comparison to Ag-platedTypically, 30 samples is inspected under 10xmicroscope unless otherwise specified. 2.2 Epoxy Dispense Scale Assessment

Due to the poor wettability of the Ag-baseroughened µPPF which results in insufficient eat the chip corners, a full epoxy coverage undeand a consistent linear epoxy fillet height formaTo achieve this, the epoxy dispense scale is vaat 80%, 90% and 100% to determine the opscale that can satisfy the target epoxy response.pressed down onto the dispensed epoxy glue targeted height (Figure 4) until the epoxy g

ly; (a)Die surface

Analysis his study come

material of the ess of 0.25 mm. of ~500 nm is full layer of Pd on the first Ni

h a thickness of surface. The

ve the adhesion pound. A final applied on the

sed to compare The surface

tly affects the ularly after the he die bonding e Ag-plated Cu

m, of the same ght as a critical chip thickness. tion scope after

the leadframe ndicular to the Mathematical the actual fillet

n, the study is uipment, epoxy justment on the adframe type as

contrast under d Cu leadframe. x magnification

d epoxy on the epoxy coverage erneath the chip ation is needed. aried (Figure 3) ptimum pattern The Si chip is gradually at a

glue covers the

periphery of the Si chip. 30 samples pattern scale are prepared. The filletcomparison and other functional tests(BLT), die tilt, voids are also checkedno assembly variation.

Figure 3 Schematic diagram of dispense patt100%.

Figure 4 Schematic diagram of die bonding pro

2.3 Die Bond Parameter, Design of Ex

After the optimum epoxy dispensesection 2.2, it is then set as a fixed inpassessment. Utilizing SAS JMP experiment (DoE) is set-up to iparameter range that can best satisfyfunction requirements (Table 1) putfillet height response.

Table 1 Die bond functional test response and r

The following critical parameters

previous studies and based on their behavior during die bonding procesbonding equipment: dispensing heighand component placement over travel.matrix (15 legs Box-Behnken) gensurface methodology (RSM).

for each epoxy dispense t height is inspected for

s i.e. bond line thickness d during set-up to ensure

tern scales at 80%, 90% and

ocess step.

xperiment e scale is identified from put parameter on the next

software, a design of identify the optimized y the target die bonding tting emphasis into the

requirements .

s are selected based on influence on the epoxy

ss using a specific die ht, pattern spindle speed Table 2 shows the DoE nerated using response

342 2013 IEEE 15th Electronics Packaging Technology Conference (EPTC 2013)

Table 2 RSM DoE Matrix

Dispensing height is the distance from the Dwhich the adhesive is extruded through the nthe formation of a dot shape. It should be allow the fluid to contact the DAP surface withso that the epoxy glue is pulled from the neneedle leaves the dispensing position [5]. Pspeed is the speed of the dispenser speed screwplacement overtravel is defined as the overtratool onto the component during placement. Tospring characteristic curve of the tool, the ovethe forces which the tool applies to the compovalues lie between 0.2 to 0.9 mm.

3.0 RESULTS AND DISCUSSION 3.1 Surface Morphology of Roughened µPPF Cu Leadframe

The SEM pictures in Figure 5 showmorphology of the Ag-plated Cu leadframe (F5(b)) and roughened µPPF surface (Figure taken at 10Kx and 50Kx magnification. morphology of the Ag-plated Cu leadframesmooth (Figure 5(a)) compared to roughened5(c)) [4]. It has a non-uniform Ag grain deposisizes that range from 100nm to 800nm (Figusurface morphology of roughened µPPF hamushroom-shaped grains with a size of about 55(d)). These mushroom-shaped grains and roumorphology have greatly improved the interlothe leadframe surface and the moulding comhelps to improve the package reliability perform

(a) (b)

DAP surface at needle allowing low enough to

h sufficient area eedle when the Pattern spindle w. Component

avel of the pick ogether with the ertravel defines

onent. Practical

and Ag-plated

w the surface Figure 5(a) and 5(c) and 5(d)) The surface e is relatively

d µPPF (Figure ition with grain ure 5(b)). The ave a uniform 500 nm (Figure ughened surface ocking between

mpounds, which mance.

(c)

Figure 5 SEM of Ag-plated Cu leadframe surfa10k and (b) 50k ; SEM of roughened Ni/Pd/Aumagnification of (c) 10k and (d) 50k [4].

3.2 Epoxy Fillet Height Comparison oAg-plated Cu Leadframe Fillet height comparison of roughand Ag-plated Cu leadframes (Figuepoxy fillet height on the roughenehigher compared to the latter. Figuheight response for an Ag-plated Cu leeven epoxy coverage from edge to edgSi chip was observed. For the rougheit is observed that the epoxy squeezelike formation along the sidewall of thof the epoxy glue goes beyond the height and eventually reaches 90%midspan of die edge. This is due to tthe DAP surface coupled with (roughened) of the µPPF surface that DAP surface. Instead of wetting leadframe, the volume of epoxy tendsdie side wall during die bonding. Tcapillary action of the epoxy resin (sidewall results into die contaminatiobeing contaminated as well.

(a) Figure 6 Fillet height comparison between (a)plated Cu Leadframes.

3.3 Epoxy Pattern Scale Assessment

Figure 7 shows the fillet height res100% epoxy dispense scale. The fil100% show a complete and a consisteas compared to the 80% epoxy dispglue coverage on the corners of the100% are complete, where as minimwith mountain like formation are obspeak of the chip, respectively, for thscale samples. The increase in the corners of the chip provides a unifresulting to a consistent epoxy fillet heand 100% epoxy coverage at the chip c

(d) ace with a magnification of (a) -Ag plated lead surface with a

of Roughened µPPF and

hened µPPF (Figure 6(a)) ure (b)) reveal that the d µPPF is significantly

ure 6(b) shows the fillet eadframe is linear and an ge of the side wall of the ened µPPF (Figure 6(a)), e out creates a mountain he Si chip where the peak target 75% of the fillet

%-100% fillet height at the anti-EBO content on

special pre-treatments prohibits wetting on the the DAP surface of

s to move up towards the The subsequent upward (resin bleed) on the die on with some bond pads

(b)

)roughened µPPF and (b) Ag-

sponse at 80%, 90% and llet height for 90% and ent epoxy glue coverage

pense scale. The epoxy e chip for the 90% and

mal epoxy glue coverage erved at the corners and he 80% epoxy dispense epoxy volume near the

form epoxy distribution eight across the sidewall corners.

2013 IEEE 15th Electronics Packaging Technology Conference (EPTC 2013) 343

Figure 7 Epoxy glue coverage at chip side-wall at varying d

Figure 8 shows the asymptotic relationship

dispense scale and component overtravel. Theto be pressed futher down ~0.90 mm into the epat 80% pattern scale. The travelled distanceattain the required epoxy coverage along the pSi chip, otherwise, insufficient epoxy covobserved. A lower travel distance at 0.49 mm aneeded for 90% and 100% dispense scale, obtain a good epoxy coverage along the chipplateau at 0.40mm. This shows that the wetgenerated by the roughened µPPF with compensated by the increase in the dispense scdistance is applied to obtain a consistent filepoxy coverage along the Si chip during die bon

Figure 8 Asymptotic relationship of epoxy glue pattern sovertravel.

Although a consistent epoxy glue fil

established at 90% and 100% dispense patterfails the target fillet height which is less thanthickness. This indicates that further optimizabond parameter is required to obtain a favorprocess on a roughened µPPF surface. 3.4 Fillet Height Optimization (Die Bond Param

Table 3 shows an overview of the signifparameters based on statistical analysis that functionality test done after die bonding. Cotravel and dispensing height are the critical phave a significant impact on the processability o

dispense ratio.

p of the epoxy e Si chip needs poxy dispensed e is needed to

periphery of the verage will be and 0.40 mm is respectively to p and starts to tting resistance anti-EBO was

cale as minimal llet height and nd process.

ize and component

llet height is rn scale, it still n 75% of chip

ation on the die rable die bond

meter DoE) ficant die bond can satisfy the omponent over parameters that of the epoxy on

the roughened µPPF. Pattern spindlesignificant effect and can be set as a co

Table 3 Overview of die bond significant param

Figure 9 shows the prediction pl

statistical analysis show the compsignificant factor at F = 0.0015, idispensing height at F=0.0305 is slight

Figure 9 Epoxy fillet height prediction plot.

Although the pattern spindle speed

on statistical analysis, a workable parensure consistent epoxy coverage. Thgenerated in Figure 10(a) at 3.7 mmshowed an incomplete dispense pagradually until a full and consistent gluachieved at 3.9 mm/s (Figure 10(b)).

(a) Figure 10 Epoxy pattern formation at (a)3.7mm

Based on the contour profiler set a

the die bond process parameter windored box, was determined. This hovalidated on an assembly build witensure manufacturability of the identif

e speed, however, has no onstant.

meters

lot for the fillet height, ponent overtravel is a its interaction with the tly significant.

d is not significant based rameter is still needed to he pattern spindle speed

m/s (lower specification) attern, it was increased ue pattern formation was

(b)

m/s and (b)3.9 mm/s

at 3.9 mm/s (Figure 11), ow, indicated by a small owever, still has to be th a higher quantity to fied process parameters.

344 2013 IEEE 15th Electronics Packaging Technology Conference (EPTC 2013)

Figure 11 Die bond process parameter based on 3.9 mcontour profile

Table 4 outlines the proposed die bond pro

validation matrix at Low-Low (LL), Low, NomHigh-High (HH) values. To test the robustnesswindow, LL and HH are considered in the valiset 10% of the high and low values, respectivel

Table 4 DOE validation matrix

Table 5 shows the average, minimum

functionality test result summary of the validaBLT, die tilt, voids and DST passed mrequirements. For fillet height, the measuremenat high (max at 76%) and eventually reach maxheight at HH.

Table 5 Die bond functionality test result for the validation

Figure 12 (a) shows the box plot of epoxy each condition. Individual data points, represedots, for high and HH conditions indicate ~ 5~90% values, respectively are > 75% of the filhigh fillet height measurements at high and were confirmed by the actual fillet height phot12 (b).

mm/s spindle speed

ocess parameter minal, High and s of the process idation and was ly

and maximum ation run. The

minimum target nts starts to fail x of 100% fillet

n run.

fillet height for ented by black

50% values and llet height. The HH conditions tos from Figure

(a)

(b) Figure 12 Validation run sample results: (a) Ep(b)Epoxy fillet height and epoxy coverage photo

The proposed DA parameter wind

to the results of the validation (Tavalidation run at High setting is adjustments.

Table 6 Optimum parameter window

Re-validation run, set-up at high papositive results. DA functional test reon the confirmation run pass all targetest with a linear and consistent epinspection (Figure 13).

Table 7 DA functional test results for re-validat

Epoxy fillet height box plot and o

dow is reduced according able 6) and thus a re-

made to verify these

arameter setting, shows esult summary (Table 7) et requirements for each poxy fillet height after

tion run.

2013 IEEE 15th Electronics Packaging Technology Conference (EPTC 2013) 345

Figure 13 Epoxy fillet height coverage for re-validaparameter setting.

It is also proved that with the identi

parameter roughened µPPF is able to achievfillet height, zero die contamination due higheight and good die bond yield in a large quanti

4.0 CONCLUSIONS The paper studies the interaction of the Ag-

the roughened µPPF with anti-EBO and identiparameter window thru DoE. It is shown thtreatment of anti-EBO of the roughened uPPF glue wetting horizontally on the DAP surfacethe epoxy further up along the side wall of tmechanism can be overcome by increasing thethru the glue dispense pattern scale. Visual insthe sidewall of the silicon chip show consistenepoxy glue coverage at higher dispense patteDoE and Box Behnken response surface methodthe critical die bond parameters clearly estabparameter window for the roughened µPPF wThe defined process window show positive resprocessability and manufacturability.

Acknowledgments The authors would like to thank Mr. Paul P

on die bond process and Mr. Muslim Dedi for S

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346 2013 IEEE 15th Electronics Packaging Technology Conference (EPTC 2013)