capillary design for common copper bonding challanges

Capillary design for common copper bonding challenges K&S and Heraeus Joint Copper Workshop 2009 Capillary design for common copper bonding challenges Capillary design for common copper bonding challenges 2 Agenda: �2nd Bond related Design � Tip Morphology � Face angle, IC angle � Outer Radius �1st Bond related Design � SIGMA II Design � CIC Capillary design for common copper bonding challenges ultrasonic tool wire Wire “Rolling” in the X direction 3 The challenges of copper bonding – 2nd bond process window (X to Y / tail strength) � The 2nd bond process in copper bonding is more sensitive to ultrasonic energy because of a rapid increase in plastic stress and much larger strain hardening compared to Au wire making it more prone to broken tail and stitch bonds. � Due to the increased hardness of copper wire and the high USG values needed to deform it copper 2nd bond is prone to the phenomena of “slippage” between the wire and capillary causing weak tail bonds in the Y axis and stitch pull differences between the X and Y axis. ultrasonic tool wire Wire “slipping back” in the Y direction Various performance related topics1st Bond related design2nd Bond related design Tail Bond Formation Capillary design for common copper bonding challenges Various performance related topics1st Bond related design 4 Capillary Tip Morphology – K&S offering Granular MattePolish 2nd Bond related design Capillary design for common copper bonding challenges Various performance related topics1st Bond related design Capillary Tip Morphology – Grip mechanism 5 � Unique granular morphology � Minimize wire slippage during bonding � Improves gripping between the wire and the capillary 2nd Bond related design Capillary design for common copper bonding challenges Various performance related topics1st Bond related design 6 FE Analysis – 2nd Bond Deformation Low Friction µ = 0.01 Sufficient Friction µ = 1.0 2nd Bond related design Capillary design for common copper bonding challenges Various performance related topics1st Bond related design 7 FE Analysis – 2nd Bond Deformation Contact area Larger Contact area Low Friction µ = 0.01 Sufficient Friction µ = 1.0 2nd Bond related design Capillary design for common copper bonding challenges 8 � Background � Short tail errors are one of the biggest (if not THE biggest) causes of reduced MTBA � If the tail bond is too weak, a process stoppage, frequently called a “Short Tail”, will occur. � Traditional 2nd DOE’s with typical sampling levels will generally not capture the SHTL response rate � K&S developed a unique method to measure in-situ tail pull strength Various performance related topics1st Bond related design2nd Bond related design Capillary design for common copper bonding challenges Various performance related topics1st Bond related design Better Gripping effect on tail bond strength ultrasonic tool wire Tail pull values in X and Y axis Application conditions • Bonder: K&S Maxum • Wire: iCu 1.3 mil • Package: Leadframe • Capillary: CuPRAplus vs. CuPRA T a i l s t r e n g t h Stronger Tail bond Smaller differences between X & Y Less sensitive to SHTL Advantages of Better wire gripping 2nd Bond related design Wire “slipping back” in the Y direction Capillary design for common copper bonding challenges Various performance related topics1st Bond related design T a i l p u l l [ g r . ] 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Min Opt Max Min Opt Max polish matte Cell [-] w ithin Design [-] X Y Axis [-] Min Opt Max Granular 10 The challenges of copper bonding – 2nd bond process - Examples Application conditions • Bonder: K&S Maxum • Wire: iCu 0.9 mil • Package: 55um PBGA • Capillary: CuPRAplus vs. CuPRA (Polish & Matte) � Higher Tail pull & Stitch pull results for CuPRAplus design � Larger more portable process window for CuPRAplus design Fine Pitch – 0.9mil Tukey-Kramer 3 4 5 6 7 8 9 S t i t c h P u l l [ g r . ] Polish Matte Design [-] Granular Design [-] Design [-] T a i l p u l l r e s u l t s S t i t c h p u l l r e s u l t s Cupra CuPRAplus 2nd Bond related design Force [gr] U S G [ m A m p ] Capillary design for common copper bonding challenges Various performance related topics1st Bond related design 11 The challenges of copper bonding – 2nd bond process - Examples Application conditions • Bonder: K&S Maxum ultra • Wire: DFH 2.0 mil • Package: 150um 68L QFP • Capillary: CuPRAplus vs. CuPRA � Larger NSOL to SHTL process window using CuPRAplus design. � Better Stitch pull results for CuPRAplus design 15 20 25 30 35 40 45 50 55 60 S t i t c h p u l l v a l u e [ g r ] Granular Polish Design Each Pair Student's t 0.05 Large wire – 2.0mil CupraCuPRAplus 2nd Bond related design Force [gr] U S G [ m A m p ] Capillary design for common copper bonding challenges Various performance related topics1st Bond related design 12 � Tip geometry selection FA, OR and ICA greatly depends on the package type and the process type used. � In general higher ICA increases Tail bond strength helping to avoid SHTL’s While being more sensitive to stitch peeling. ICA 80 ICA 40 T a i l p u l l [ d a c ] 0 5 10 15 x y x y x y x y Direction [-] 40 80 40 80 ICA [deg] 4 11 FA [deg] Application conditions • Bonder: K&S Maxum plus • Wire: iCu 0.8 mil • Package: 50um BGA • Capillary: CuPRAplus Influence of FA and ICA on 2nd bond performance 2nd Bond related design Capillary design for common copper bonding challenges Various performance related topics1st Bond related design Influence of OR size on 2nd bond performance 13 OR Comparison 1 2 3 4 5 6 7 8 0.5 1 1.5 2 2.5 OR [mil] S t i t c h P u l l OR= 0.5mil OR <0.1 mil � Typically small OR sizes are recommended as they improve stitch pull and help minimize X/Y differences in copper bonding OR 0.1milApplication conditions • Bonder: K&S Maxum plus • Wire: iCu 0.8 mil • Package: 50um BGA • Capillary: CuPRAplus Application conditions • Bonder: K&S 8028PPS • Wire: iCu 1.0 mil • Package: 60um PBGA • Capillary: Cupra OR 0.3 mil OR 0.1 mil 2nd Bond related design Capillary design for common copper bonding challenges 2nd bond design highlights � CuPRAplus unique design improves gripping force wire and capillary � CuPRAplus unique capillary design helps: � Stronger tail bond � Reduced differences between axis � Reduced SHTL sensitivity � Attain a Larger process window � CuPRAplus design is applicable for both fine wire and large wire applications � Higher ICA helps strengthen the tail bond but may be more sensitive to stitch peeling � Small capillary Outer Radius may help reduce X/Y stitch pull differences 14 Various performance related topics1st Bond related design2nd Bond related design Capillary design for common copper bonding challenges Various performance related topics2nd Bond related design1st Bond related design 15 The challenges of copper bonding – Pad damage Copper process have roughly a 25% increase in the maximum stress compared to an equivalent gold ball bond Cratering Metal lift Al splash Capillary design for common copper bonding challenges Various performance related topics 16 0 1 2 3 4 5 D e l t a s p l a s h [ u m ] 1 2 1 2 1 2 1 2 Smaller CD 1.4 ICA 120 ICA 90 Sigma Cap No. [-] within Design [-] *Lower is better 40xmeasurements 2xcaps m in im um sp las h Delta Splash -- == Etched pad Bonded ball *Copper ball etched off pad using Nitric acid Delta splash in the Y direction measured Application Conditions • Bonder: K&S Maxum ultra • Wire: Maxsoft 1.0 mil • Package: 60um BGA • Capillary: CuPRAplus Capillary design Vs. 1st bond Aluminum splash 0.0 0.5 1.0 1.5 2.0 2.5 3.0 D e l t a | Y s p l a s h [ u m ] Non-Scrub Scrub Process [-] 40xmeasurements 1xcaps *Lower is better 1st bond scrub influence on splash amount 2nd Bond related design1st Bond related design Capillary design for common copper bonding challenges Various performance related topics 17 � SIGMA II capillary design required significantly lower US energy to provide the same ball size as conventional designs � Use of 1st bond Table scrub provided significantly lower Al splash at same ball size. �SIGMA II Design had the lowest amount of splash while retaining the same Shear / UA as conventional design B a l l S h e a r / U A [ g r / m i l ^ 2 ] 6 7 8 9 10 11 MIN OPT MAX MIN OPT MAX MIN OPT MAX MIN OPT MAX Ref Sigma CD 1.4 ICA 120 Cell [-] w ithin Design [-] B a l l S h e a r / U A [ g r / m i l ^ 2 ] 6 7 8 9 10 11 MIN OPT MAX MIN OPT MAX MIN OPT MAX MIN OPT MAX Ref Sigma CD 1.4 ICA 120 Cell [-] w ithin Design [-]Ref Sigma CD 1.4 ICA 120 ICA 90 ICA 90 ICA 90 ICA 120 RefRef Sigma CD 1.4 ICA 120 CD 1.5mil CD 1.5mil CD 1.4mil CD 1.5mil Ref Sigma CD 1.4 ICA 120 Capillary design Vs. 1st bond Aluminum splash -Continued- SIMGA II capillary design 2nd Bond related design1st Bond related design Ref & Smaller CD ICA120 SIGMA II Capillary design for common copper bonding challenges Various performance related topics CIC capillary design for copper bonding 18 Application conditions • Bonder: K&S Maxum ultra • Wire: Maxsoft 0.9 mil • Package: 60um PBGA • Capillary: CuPRAplus � While maintaining same ball size K&S CIC6 design provide significantly lower Stdev. Smaller Stdev. 2nd Bond related design1st Bond related design Capillary design for common copper bonding challenges 1st bond design highlights � SIGMA II capillary design help lower the amount of aluminum splash generated during 1st bond formation � CIC capillary design can lower ultrasonic values and improve shear/UA stdev. 19 Various performance related topics2nd Bond related design1st Bond related design Capillary design for common copper bonding challenges 20 Company Copyright This PowerPoint presentation and all of its contents are protected under International and United States Copyright laws. Any reproduction or use of all or any part of this presentation without the express written consent of K&S is prohibited.