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Gaiser Capillary

FINE PITCH CAPILLARY BASIC

DESIGN DIMENSIONS

Fine pitch capillaries have two basic sets of industry

standard dimensional characteristics: large geometry and

small geometry. Large geometry dimensions generally

refer to the shank, back hole, and cone. Small geometry

dimensions refer to the tip and angle bottleneck details.

As with standard capillaries, fine pitch capillaries

share the basic common dimensions such as shank

diameter and overall tool length. The major dimen-

sional differences exist at the tip details of the tool and

in the specialized angle bottleneck construction.

Wider cone angles, such as 50°, and more narrow cone

angles, 20°, are often preferred over the standard 30°

cone angle for ultrasonic tuning and package clearance

reasons.

Industry standard large geometry dimensions:

1.Shank Diameter (SD)

2.Tool Length (L)

3.Cone Angle or Main Taper Angle

4.Back Hole

Figure https://www.sodocs.net/doc/4b6249354.html,rge geometry dimensions

Industry standard fine pitch small geometry dimensions:

1.Tip Diameter (T)

2.Hole Diameter or Size (H)

3.Chamfer Diameter (CD or B)

4.Inside Chamfer (IC)

5.Inside Chamfer Angle (IC Angle)

6.Face Angle (Note: may be flat, 0°)

7.Outside Radius (OR)

8.Angle Bottleneck Angle (AB or ABTNK Angle)

9.Angle Bottleneck Angle (AB or ABTNK Height)

Figure 46.Small (tip) geometry dimensions

Figure 45.Angle bottleneck (ABTNK or AB) geometry

dimensions

FINE PITCH PROCESS REQUIREMENTS

Below are some basic requirements for fine pitch bonding processes:1.Consistent wire diameter 2.State-of-the-art wire bonder

3.Substrate material and design for fine pitch process

4.Capillary bottleneck designs and materials

5.

Molding and mold compound suitability

PROCESS OPTIMIZATION

The following are some general quality guidelines and requirements for optimization in a typical fine pitch bonding application:

1.Ball shear ratio > ~ 6 gm/mil 2

2.Pull strength > ~ 6 gm

3.Bonded ball size for fine pitch = 1.8 to 2.2 times the

wire diameter

4.Bonded ball size for ultra fine pitch = 1.5 to 1.8

times the wire diameter

5.Capillary tip diameter = 1.28 times the pad pitch

CAPILLARY DESIGN CONSIDERATIONS

The bond pad opening (BPO) restricts the size of the bonded ball and the bond pad pitch (BPP) controls the optimum size of the capillary tip diameter that can be used. It is essential that the bonded ball be placed completely within the BPO. The capillary tip diameter must be large enough to provide a strong second bond but also clear any adjacent wires during the bonding process.

1.Hole Diameter (H): For fine pitch applications, a hole to wire clearance can be 0.0003 in./7.6μm for 70μm-90μm pitch, 0.0002 in./5μm for 60μm pitch, and 0.00015 in./3.5μm for 50μm pitch bonding. This is critical to insure good wire movement with the hole during looping without causing wire drag resulting in sagging, wavy, or tight loops.

2.Chamfer Diameter (CD or B): The contribution of the CD is to control the bonded ball size. With the bond pad opening (BPO) as a limiting factor, the

selection of the proper CD is very important. Typically,the IC size for 0.0009 in./23μm to 0.0010 in./25μm wire is 0.0002 in./5μm to 0.00025 in./6μm. When using 0.0012 in./30μm wire, the typical IC size can range from 0.00025 in./6μm to 0.0003 in./8μm.3.Inside Chamfer Angle (IC Angle): The most

common angle for fine pitch bonding is 90°. For some ultra fine pitch applications, an angle of 40° to 70° is selected to reduce the bonded ball size. Poor ball shear results may stem from these steeper angles.

4.Angle Bottleneck Angle: This angle is critical for the capillary to avoid contact with adjoining loops during wire bonding. Generally, 10° is recommended but 5° may be required for some ultra fine pitch applica-tions.

5.Angle Bottleneck Height: The height required depends on the critical loop heights immediately adjacent to the capillary or those wires which the

capillary must pass between when bonding to staggered bond pads. A standard height is 0.010 in./254μm.6.Tip Diameter (T): Optimal tip diameter selection is determined by the BPP and the desired loop height to be cleared. Loop configuration must also be considered when bonding in the corners of some devices.

Figure 47.Process 1800 style angle bottleneck

FINE PITCH WIRE BONDING

The miniaturization and shrinkage of silicon chips

has lead to considerable wafer cost savings. However, it

requires much closer wire to wire spacing, smaller

deformed ball bonds, and complex looping to prevent

looping problems. In order to support and challenge

the ultra fine pitch technology roadmap, Gaiser Tool

Company utilizes state-of-the-art enabling technologies

to gain competitive advantages.

PROCESS 1800

As the semiconductor industry moved to finer and

finer pitches, the demand for smaller angle bottleneck

tip diameters and tighter dimensional tolerances grew.

Gaiser Tool Company recognized this need and devel-

oped the Process 1800 manufacturing process.

Process 1800 eliminated the previously standard

grinding operation now leaving the angle bottleneck

portion with a high-tension, mirror smooth, secondary

alumina skin.

The newest bottleneck manufacturing technology

providing superior bottleneck strength

Increased shear strength and rigidity

Superior ultrasonic energy transmission and a wider

tuning window

Substantially tighter dimensional tolerances

Reduced standard deviations

Sub-micron average grain size, near-zero porosity

of the ceramic and zirconia toughened ceramic

materials

Ideal for high-frequency transducers

Figure 48.Example of the chamfer diameter radius (CDR)

THE CHAMFER DIAMETER RADIUS

(CDR)

The chamfer diameter radius (CDR) was developed to

eliminate cut tail problems on new fine pitch devices.

This design is a blending where the IC meets the face

of the capillary:

Blending of IC and tool face

Minimizes cut tail problems

Reduces effects of flame-off error

Figure 50.Gaiser s CZ1 -Zirconia toughened Alumina ceramic:

Less than 0.7μm grain size,zero porosity

Figure 49.Gaiser s standard Alumina ceramic material:Less than 2μm grain size,near-zero porosity

CZ1 MATERIAL - ZIRCONIA

TOUGHENED ALUMINA CERAMIC

Gaiser s CZ1 material is designed for world class,high-speed, fully automatic wire bonders. It is ideal for ultra fine pitch, low-loop, and long-loop bonding applications. When combined with Process 1800, the CZ1 capillary produces the ultimate ultra fine pitch capillary. 100% and greater increases in angle bottleneck break strength vs. conventional capillaries Longer tool life, reduced cost per bond

Ideal for standard and high-frequency transducers Improved internal bore surface provides reduced wire drag for enhanced looping and wire control

Sub-micron average grain size

Figure 52.Ball bond for a 70μm QFN package made with part number: 1851-13-437P-35(2-8D-8)20D-AB10x10-CZ1

Figure 51.Example of a QFN package

NEW PACKAGE DEVELOPMENT

MICRO-LEADFRAME / QFN PACKAGES

The QFN (Quad Flat Non-leaded) is at the top of the list of rapidly growing popular devices in the IC industry today. Comprised of a CSP plastic encapsu-lated package with a copper leadframe substrate, its small size and low profile make it ideal for high-density PCB s used in small scale electronic applications such as cellular phones, pagers, and PDA s. It is becoming part of the lower cost, low pin count SOIC, TSSOP, Mini-BGA, DIP, and QUAD configurations.

The two common types of leadframes are silver spot plated leads or nickel-palladium preplated. These leadframes are pre-taped with film at the bottom and ready to use for production. Success for bonding this package requires the following: Lead frame design

Mold compound selection Polyimide file selection Window clamp design Choice of bonder

Bonding parameter optimization

Failure to optimize the above selections may result in the following: Broken ball neck

Weak and stressed ball neck line Poor stitch/crescent bond formation

Weak pull strength

Reasons for the previous problems are as follows: Too much induced lateral movement and vibration of the already bonded units within the strip of devices during the bonding process

Resonance effect of the units of the strip under the work stage during bonding

High elasticity of the laminated film absorbs too much of the bonding energy resulting in significant second bond weakening and failure

The following efforts are being pursued in order to refine and optimize the QFN package:

Selection of the polyimide film of the pre-tape leadframe

Selection of the mold compound for lead-bleed prevention

A suitable solution to the various CTE effects to the overall package integrity

Some package engineers have resorted to ball bumping on the lead side to reduce the vibration and create a more rigid base for the second bond. For a 70μm pitch QFN package, Gaiser Tool Company has developed a T=0.0035 in./89μm with an 8° face angle capillary (1851-13-437P-35(2-8D-8)20D-AB10x10-CZ1). This capillary has achieved a mid-span pull strength of 4.5grams, maximum pull strength of 7.4 grams, and an average pull strength of 6.0 grams.

Figure 53 & 54.Stitch bonds for a 70μm QFN package (in X (above) and Y (below) directional scrubs) made with part number: 1851-13-437P-35(2-8D-8)20D-AB10x10-CZ1

Compared to gold wire, copper wire offers higher mechanical strength, lower electrical resistance, and greater tensile strength. Additionally, copper wire bonded to copper pads provides better monometallic contact.

The need for inert gas used to protect the balls during formation and protect the copper pads from oxidation is a disadvantage. Also, the harder copper ball formed may push away the softer aluminum pad material during ball bonding which may lead to an increase in ball bond lifting. This can be reduced by bonding copper wire to a copper pad.

Capillary selection for copper wire bonding in-cludes large tip diameter designs if possible to assist with the crescent bond formation. Plasma etching may also aid in copper wire bonding. An 11° face angle and a large CD dimension are also advantageous to crescent bond formation. Gaiser s CZ1 material provides a longer tool life than the standard alumina ceramic when using copper wire.

CHIP SCALE PACKAGES (CSP)

The two most popular types of CSP s use either flex (polyimide) or rigid BT laminate. Both require low temperature bonding. A larger capillary tip diameter is recommended for better crescent bonds, if the pad pitch will allow, and high-frequency ultrasonic systems.

For most CSP s, very short wire loops are required so that the crescent bond can be made close to the die edge. This normally requires a bottleneck design capillary. The bottleneck height may need to be taller than usual in order to avoid contact with the die edge.CZ1 material is also recommended for its longer life potential.

Figure 55.Side view of stitch bond showing exhibiting good transition from the wire to the bond.

COPPER BALL BONDING

Copper ball bonding is gaining acceptance as IC manufacturers are investigating the replacement of aluminum metallization on the die pad with copper to increase performance and lower device cost. Copper wire is recognized as a possible replacement for gold wire in fine pitch applications.

Figure 56.Cavity-up enhanced ball grid array (CUEBGA)package that incorporates a stiffener laminated with adhesive to the polyimide flex circuit

Figure 57.50μm pitch capillary

50μm PITCH BONDING

As the IC industry pushes toward finer pad pitches

to support the shrinking of silicon chips, the most

challenging tasks have become obtaining small ball size

consistency and reliable crescent bonds without short

tails, missing wires, or EFO errors during continuous

operation. The consistency of the free air ball (FAB)

plays an important role for the eventual bonded ball

diameter and ball height. EFO current and time control

the amount of melted volume of the FAB. Gaiser Tool

Company has tested part number: 1851-9.5-437P-

25(1.25-8D-5)20D-AB5x8-CZ1 for this application on

both the K&S 8028 PPS and ASM 339 Eagle bonders

with 0.0008 in./20μm gold wire on a BGA package to

obtain the following results:

Figure 58.50μm pitch ball bonds

Figure 59.50μm pitch stitch bond

Figure 60.50μm pitch package using 0.0009 in./23μm

gold wire

Figure 61.Ball bonds in a 50μm pitch package using 0.0009 in./23μm gold wire.

Figure 62.Package with complex looping profile incorporating a two-tier lead design.

Figure 63.Ball bond made with 0.0012 in./30μm gold wire for 100μm pitch package.Smashed ball = 0.0027 in./68μm

Figure 64.Ball bonds made with 0.0012 in./30μm gold wire for 80μm pitch package.

Figure 65.Stitch bond width is equal to twice the wire diameter.

Figure 66.Stitch bonds made with 0.0012 in./30μm gold wire.

Figure 71.The 30μm ultra fine pitch capillary T = 0.00165 in./42μm H = 0.00075 in./19μm

FUTURE FINE PITCH PACKAGES

Current users are beginning to make internal studies of 50μm pitch capabilities in efforts to stabilize and

optimize processes for mass production. As the challenge to reach finer pitches of 45μm and 40μm begins, the bonder manufacturers are looking ahead and developing equipment for 35μm pitch using 0.0006 in./15μm wire,and 30μm pitch with 0.0005 in./13μm wire.

Gaiser Tool Company is working in partnership with several bonder and wire manufacturers by providing the necessary capillary designs to meet these new challenges.

Figure 67 & 68.Ultra Fine Pitch (35μm) Capillary vs. Standard Pitch (175μm-225μm)Capillary. The tip diameter (0.0018 in./46μm) of the ultra fine pitch tool (left) will fit into the same hole diameter as that of the standard capillary (right).

Figure 70.Ball bonds made with a 35μm ultra fine pitch capillary

Figure 69.Stitch bonds made with a 35μm ultra fine pitch capillary

IMPORTANT ELEMENTS FOR FINE PITCH APPLICATIONS

Important Elements for Determining the Proper Tools in Fine Pitch Wire Bonding Applications

Bond Pad Pitch:The distance between the centers of the bond pads.

Bond Pad Size:May be square, rectangular, or round. The most important dimension is the size along

the pitch, as shown above.

Loop Height:The most important aspect of wire loop height is the effective critical loop height

directly adjacent to the capillary. If the capillary is designed to clear only the maximum

loop height which occurs away from the capillary, then the T dimension will be less

than required resulting in a less than ideal second bond.

Critical Clearance:The design clearance between the capillary angle bottleneck, capillary manufacturing

tolerances, loop control, and desired quality standards can all influence the designed

clearance.

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