Wire Bonding Technology.docx

1、Wire Bonding TechnologyWire Bonding Process Editor:Thomas-ma1.Ball Shear Test - Failure Mode Grading MethodThe failure modes used in the ball shear test help to evaluate the bonding results and assess the bonding process.Failure Modes:Ball lift indicates bad results (lowF)：Gold remain indicates good

2、 results ( highF)Pad peeling or cratering indicates a flow that should be investigatedFactors affecting theF:Bonded area (D)ProcessShear height (5 um)Tool size (min 2XD)Ball tool centeringCleanlinessTester calibration, accuracy and vacuum2.Wire Pull Test - Failure Mode Grading MethodThe failure mode

3、s used in the wire pull test help to evaluate the bonding results and assess the bonding process.GradeBroken atReasonQuality1Ball liftBad processPoor2Ball neckH.A.ZGood3WireDepends on conditionsVery good4WeldWeld deformationGood5Stitch liftBad processPoorFactors affecting theF:Wire diameterWire leng

4、thLoop heightPad to lead plane gapProcessHook locationTester calibration, accuracy and vacuum3.ball height (thickness)ball (1st bond)3. Bottleneck (BTNK) Capillary Bonding4.BottleneckCapillaries Tolerances TableFamily/DesignBond Pad PitchSpec RangeTolerances (mils)TipHoleCDOR4149X4849XAbove100 umReg

5、ularFor Tip100.3For Hole2.5+0.25 / -0.10.2For OR3.50.3For Tip100.2For 1.8Hole2.5+0.2 / -0.10.2For OR3.50.2For Hole1.8+0.15 / -0.10.2HighSpec0.1-0.1 / -0.00.10.25.Loop heightmeasuring6.Optical MeasurementsUsually this is the first set of examinations to be performed, using a Scanning Electron Microsc

6、ope (SEM) and advanced optical equipment.These examinations are performed both prior to the bonding process - to determine the best tool and process parameters - and after its completion - to evaluate the bonding results. These examinations consist of:Inspection of thepackage/ device dimensions, whi

7、ch assists in setting the process specifications, determining the wiring constraints and designing the best-suited capillary.Inspection of thebond pad and pitchand related dimensions, which assists in determining the required bond pad opening, pads gap, pad size and pad pitch. This also helps to det

8、ermine the bondable area and the required cross section (according topassivation layerand pad layer thickness).Inspection of thewiring measurements, which assist in defining the required ball size, ball height, ball placement accuracy, loop height and wire sway tolerances.The post bonding inspection

9、s includeball (1st bond) diametermeasuring,ball height (thickness)measuring andLoop heightmeasuring.7.Bond Pad PitchThe bond pad pitch is a defined distance between the centers of two adjacent pads. The desired pad pitch, derived from the application constraints, prescribes the type of capillary one

10、 should use.The capillarys external dimensions (Tip,BTNK,CA) need to be optimized in order to avoid contact between the capillary and the adjacent wire while maintaining optimal bonding performances.8.The 1st bond diameter is derived from thepad opening.Most applications require a 100% bond on pad.

11、The most important capillary parameter affecting the in-spec accuracy of the 1st bond is theICvolume, which consists of theHolediameter, theICAandCD.This parameter needs to be carefully controlled and optimized in ways that shall be discussed later.9.Wire DiameterThe wire diameter is defined by the

12、application - finer processes naturally employ thinner wires. Therefore. the capillaryHoleis defined by the desired wire diameter. Generally, thick wires are preferable due to their strength and better resistance to sweep during molding. However, there is a delicate balance between Hole and wire tha

13、t needs to be observed in order to maintain the critical gap that allows the free and uninhibited movement of the wire. This critical gap is imperative for the success of the process and eliminating incidents of wire sway and wire friction. Another factor influencing the wire diameter selection is t

14、he cost of thegold wire.10.K&S Capillary Design RecommendationsWire Diameter(mil)Recommended Hole(mil)Min. Recommended Hole(mil)2.003.002.401.502.201.801.301.801.501.201.701.401.101.601.301.001.501.200.901.201.100.801.000.950.700.900.8511.Technical GuideGood bonding results are the primary goal of e

15、very bonding process. These results are then compared to the specifications (SPEC) defined by the semiconductor manufacturer and judged by their deviation from that SPEC. The semiconductor manufacturer seeks process reliability at lower costs and higher yields. These obvious business targets are ach

16、ieved through a repeatable and stable bonding process. Process stability is measured according to the following performance specifications:Free Air Ball diameter (min, max, std, Cpk)Ball diameter & height (min, max, std, Cpk)Loop height & shape (min, max, std, Cpk)Ball shear force & Strength (min, C

17、pk)Wire pull force (min, Cpk)Ball placement accuracy (min, Cpk)Confirmation run (stability, number of assists, visual inspection,UPH)Capillary dimensions tolerances (SPECs, effect on process, lifetime)Overall process feasibility (cost, demand, time to market)K&S Bonding Tools has designedadvanced pe

18、rformance teststo determine whether specifications were met. Understanding the relationship between capillary dimensions and bonding results is the key to controlling the bonding process. Every tool has more than 15 different parameters that determine the bonding results. These parameters, along wit

19、h various other factors such as the bonding machine, the wire and the device make up the complex environment that influences the process. This environment is analyzed by bonding experts in K&S application labs and R&D centers. The following is a general description of the capillary-process relations

20、 that by no means conclude the bonding results analysis.12.Ball Shear TestThe ball shear test is performed using a Shear Tester (BT-24, BT-2400 PC, DAGE 4000) and a Shear Tool.The test is consistent with the following methodology:1.Measure ball diameter (D) and ball height (H), and then calculate th

21、e bonded area (S).S = (D2)/4*pin mil2 or um2.2.Fix shear height according to ball height and passivation thickness.3.Perform Shear force test. The Shear force (F) is measured in gr.4.The force value obtained is calculated as follows:S/u_a (Shear per unit area)= Shear /pD2/4.Reasonable strength range

22、 = 5.5 and above gr./mil213.The Effect on the 1st BondThe 1st bond is primarily affected by theIC. The IC centers theFABprior to the formation of the bond, transmits ultrasonic power to the ball, and helps to control the size of the bond. TheCDand theICAdetermine the IC volume, which in turn determi

23、nes the shape, diameter and strength of the 1st bond. There are two main factors affecting the strength of the 1st bond:1. The force vectors applied by the ICA andTipface.2. The ultrasonic vibrations applied to the FAB, which is captured in the IC volume.The ICA also affects the force vector applied

24、 on the gold squash. In most cases the larger the ICA, the higher the pressure applied on the squash. K&S Bonding Tools offers various ICAs for different application requirements, ranging from 60 to 130. The most common ICA dimensions are 90 and 120. The 120 ICA is usually applied to standard applic

25、ations where a larger squash is permitted. The 120 ICA allows more gold to flow outside the IC, thus utilizing the tip face for a stronger 1st bond.In Fine Pitch applications, where smaller squashes are required, enlarged IC volume is needed to capture more gold. In these instances, 90 ICA is approp

26、riate. In this case, the IC volume is of more importance than the Tip face as a means of transmitting the force and ultrasonic vibrations needed to strengthen the 1st bond.14.The Effect on LoopingThe main capillary parameters affecting looping are theIC type and theHole. To ensure stable looping, it

27、 is critical to reduce occurrences of friction between the wire and the capillary. During looping, the wire comes in contact with the capillary along the Hole, when touching the corner of the Hole and IC and when going through the corner of the IC and theTipface. When excess friction occurs, these c

28、ontacts can result in wire damage and loop sways.To avoid these setbacks in looping one needs to define an appropriate gap between the Hole and the wire, determine the bestICA, and select additional features such asD/ICorIR. The minimum hole-wire clearance is usually set at 0.2 mil for Fine Pitch ap

29、plications; when finer clearances are required, there is difficulty in reducing gaps without damaging looping. Kulicke &Soffa industry-leading tolerances allow such reductions while maintaining a stable process. In Standard capillary design, the loop height determines the CA, while in Fine Pitch cap

30、illary design, the loop height determines theBTNK height,BTNK angleand BTNK radius. For long and high looping, a D/IC with a 90or 120 angle is usually recommended. For long and low looping, an IR and ICA of 120 are advisable. Naturally, these recommendations are subject to application constraints an

31、d optimization considerations.15.The Effect on the 2nd BondThe capillary affects the 2nd bond in two main aspects:The stitch bond - this bond permanently connects the wire to the lead. (More about the stitch bond)The tail bond - this bond temporarily connects the wire to the lead. It enables the capillary to rise to the tail position, t