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QFN Package Copper & Gold Wire Bonding Capillary

As the consumer market aggressively demands for the miniaturization of electronic products with more functionality, the requirement for small IC components has significantly increased, particularly on QFN packaging. Two major advantages of QFN over other leaded packages are - cost to manufacturer (for small, thinner, lighter in size, hence promoting more units per lead frame) and improved performance ICs (for better thermal dissipation and reduction in lead inductance).

In general, QFN packages are available in two types - a punch type and a sawn type. A sawn type typically comes with a polyimide tape before die attach or wire bond process. The purpose of the tape is to prevent the bleeding of the resin from the molding compound into the backside of the QFN leadframe. However, the polyimide tape causes the lead to bounce when exposed to high temperature coming from the heater block.

Tapeless QFN
TAPELESS QFN
punch type 
TAPE QFN –
Polyimide Underneath Strip


Challenges of Bonding QFN

QFN wire bonding has its own special characteristics as compared with other leaded packages. Looking at the wire bond process set up, QFN is much more complicated than other packages and these are highly influenced by the following three factors, as shown in Figure 1 below:

Figure 1 – Factors affecting  QFN Bonding

The QFN package tie bar width and thickness design greatly affect the wire bonding performance. Wider and thicker lead configuration are preferred as this will have lower reaction towards leads bouncing during  the wire bonding process. Lead bouncing is more prominent on tape QFN where the tape actually “softens” when subjected to high bonding temperature of equal or more than 200˚C. The “softening” effect will absorb certain amount of USG power needed for better weldment of  the wire  to the lead surface to form the stitch.


The effect of  QFN matrix leadframe made it impossible to design a clamping system which will hold the middle fingers at the center of the bonding area
(Figure 2). Under this condition, the best way to clamp or hold QFN matrix leadframe would be around its perimeter. Consequently, this leaves the middle of the QFN matrix leadframe area prone to micro bouncing. The micro-bouncing effect will always be inherent with the QFN bonding (with tape underneath), causing some instability issue in second bond deformation.

In a typical stitch bonding (second bond) process, the use of lesser USG power setting is more preferred for QFN with tape underneath. This is to minimize the micro bouncing effect translated to the ball bond (first bond) causing ball neck stress or damage as shown in Figure 3.

Figure 2
Matrix Clamping Design
 Figure 3
Stress Mark Above the Deformed Ball

The introduction of thermocompression (a combination of force  & temperature - Figure 4) - alleviates micro-bouncing effect on the QFN matrix leadframe, resolving ball neck stress or damage. Usually, a longer bonding time of more than 15 milliseconds with high and gradually ramping up bond force profile, ranging from more than 100g to less than 500g (depending on wire size) are pre-requisites for  good thermocompression bonding. The introduction of thermocompression bonding reduces  the effect of  the micro bouncing providing better quality bonding and  smoother bonding performance that are necessary in mass volume production environment.

Figure 4: Use of thermocompression in QFN

What is SPT’s new SQ capillary?

SPT’s new SQ capillary series features a consistent surface morphology finishing used for both gold (Au) and copper (Cu) wires, specifically developed for QFN wire bonding. The SQ capillary is designed in line with thermocompression bonding concept. The uniqueness of the SQ capillary is shown in the actual bonding response in terms of higher productivity (due to improved MTBA & higher capillary touchdown) and reliability of the bonded product.

Improved MTBA

With SQ capillary, there will be lesser assist due to short tail or broken stitch which is inherent with bonding QFN package. Experience more machine uptime!



Higher Capillary Touchdown

SQ capillary coupled with optimized bonding parameters, has proven to deliver an increase in the capillary tool life as lower bond force (BF) is utilized to bond the QFN package.


Proven Reliability

Whether on gold or copper wire, the SQ capillary is designed to enhance the formation of larger & width stitch bond that will effectively increase the stitch pull reading values & longer size copper remains.


Popular Designs For Copper

Bond
Pad Pitch
µm
Useable
Wire Diameter
µm
H
µm
CD
µm
FA
°
T
µm
Recommended SPT Part Number
50 20 25 30 11 63 SQ-25063-305F-ZU39TS
60 23 28 35 11 80 SQ-28080-355F-ZU39TS
60 25 30 38 11 80 SQ-30080-385F-ZU39TS
70 25 33 43 8 90 SQ-33090-435E-ZU39TS
80 25 33 48 8 100  SQ-33100-485E-ZU39TS
80 30 38 51 8 100  SQ-38100-515E-ZU39TS
90 25 35 51 8 110  SQ-35110-515E-ZU39TS
90 30 38 53 8 110  SQ-38110-535E-ZU39TS
100 30 38 55 8 130  SQ-38130-555E-ZU39TS
110 33 41 58 8 165  SQ-41165-585E-ZU39TS


Popular Designs For Gold

Bond
Pad Pitch
µm
Useable
Wire Diameter
µm
 H
µm
CD
µm
FA
°
 T
µm
Recommended SPT Part Number
50 20 25 30 11 63 SQ-25063-305F-ZS39TS
60 23 28 35 11 80 SQ-28080-355F-ZS39TS
60 25 30 38 11 80  SQ-30080-385F-ZS39TS
70 25 33 43 8 90 SQ-33090-435E-ZS39TS
80 25 33 48 8 100  SQ-33100-485E-ZS39TS
80 30 38 51 8 100  SQ-38100-515E-ZS39TS
90 25 35 51 8 110  SQ-35110-515E-ZS39TS
90 30 38 53 8 110  SQ-38110-535E-ZS39TS
100 30 38 55 8 130  SQ-38130-555E-ZS39TS
110 33 41 58 8 165  SQ-41165-585E-ZS39TS
For less than 50µm BPP, please consult your local SPT sales

For more information and trial samples, contact your local SPT sales.

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