TANAKA TECHNOLOGIES

Bonding Lab Wire Bonding Cycle

We will focus on bonding movement, it will be explained using some animation while giving you an idea how the wire will change its shape and how it bonds.

September 2006

In this first lecture for bonding cycle, we will focus on bonding movement, can be divided approximately 4 sections. It will be explained using some animation while giving you an idea how the wire will change its shape and how it bonds.

Mr.HanaMiss BondyDr.Yama

1. What is bonding wire?

Instructor Mr.Hana:
Do you have any idea how the bonding wire is used, Bondy?
Miss Bondy:
Since I have also studied a few,I know some.A golden line is a line which connects the aluminum electrode and lead electrode of IC chip used for a semiconductor by a bonding wire like Fig.1.I have watched an image like Video1 on television.
Dr.Yama:
Dr. Yama:Hey Mr. Hana, What a chance! Why don't we teach her a bonding cycle?

Fig.1Video.1

Instructor Mr.Hana:
Let's get started!!First of all,we call the process of connecting bonding wire as a wire bonding.It is used specific machine that has capability of operating multiple bonding conditions such as about 20 cycles of bonding per second, for this process. Also as you can see on the Fig2, it is applied plenty of tools and parts for bonding process.For example,cylindrical bonding tool called capillary is used through a wire into it.And wire bonding is performed by moving a capillary.

Fig.2

2. Ball Bonding(1st Bonding)

Miss Bondy:
Mr.Hana, the tip of the wire which will come out from under the capillary is round,isn't it?
Instructor Mr.Hana:
See Video.2 of slow motion.A round portion is a ball called FAB (Free Air Ball), and is a wire tip by electric discharge.It is melted, and in surface tension,it becomes round and solidifies as it is.The diameter of this ball is made bigger than the capillary hole in order to prevent slipping wire through.

Fig.3 Video.2

Instructor Mr.Hana:
his is called Ball Bonding, although a capillary moves to the pad of IC and joins a ball to an aluminum electrode, after a ball is formed.Since it is the bonding performed first, generally it is referred to also as "1st Bonding."
Miss Bondy:
By the way, I am wondering how the ball can be bonded even though it already became hard.
Instructor Mr.Hana:
That's a good question. As for this junction, an aluminum electrode is joined to a ball with the load against which a capillary pushes a ball, the ultrasonic wave oscillated from a capillary, the heat from a bonding stage, and these three elements.Video4 shows this ball bonding process.

Miss Bondy Video.3 Video.4

3. Loop

Miss Bondy:
Mr. Hana, so in this case, next process will be 2nd bonding isn't it?
Instructor Mr.Hana:
Wait Bondy, it would be too fast to start 2nd bonding yet. In Video.5 of slow motion, it has a shape of triangle for the bonded wire, in view of width. Thus, the wire portion connected among both electrodes is called "Loop", and the important work of forming Loop is between 1st Bonding and 2nd Bonding. Loop form is decided by a motion of a capillary and the character of a bonding wire. Signs that the peculiarity is attached to the bonding wire by the motion of a capillary can be checked, letting out a bonding wire continuously, when 1st Bonding finishes it as Video.5 and it moves to 2nd Bonding points.

Video.5

Miss Bondy:
Does this loop form have any meaning? And is this always be a triangle?
Instructor Mr.Hana:
Of course, it is meaningful. Bending the wire intentionally prevent the wire to droop over the IC pad, and also avoid short-circuit by making a form tidily.Wire shape can be changed such as triangle or square etc, which is determined by various type of packages.
Dr.Yama:
Moreover, like Fig.4. At the following process of wire bonding, there is a molding process which pour resin into the whole IC and harden.A loop is fell down by resin as not bending the wire intentionally, therefore form is important.Mr.Hana, please instruct her manufacturing process of IC a day anew.

Fig.4

4. Stitch & Tail Bonding(2nd Bonding)

Instructor Mr.Hana:
The wire is connected with lead electrode by squashing the wire with capillary instead of ball forming.This process is called Stich bonding but also called as 2nd bonding. This bonding mechanism such as bond force and ultrasonic energy from capillary, the heat from bonding stage are same as ball bonding.
Miss Bondy:
Video6 of slow motion shows this 2nd bonding doesn't it? Only the capillary is going up while the bonding wire had connected with the lead electrode although it was an instant immediately after 2nd Bonding finished. Is this failure?

Video.6

Instructor Mr.Hana:
Wow you got a point! In fact, "Tail Bonding" is performed simultaneously with Stitch Bonding by 2nd Bonding like Fig.5.At Stitch Bonding, junction to a wire and a lead electrode is performed and preparations towards the following bonding cycle, i.e., preparation of ball formation, are simultaneously made by Tail Bonding.
Miss Bondy:
Wow, preparation for ball formation! Bonding cycle still hasn't finished yet?

Fig.5

Instructor Mr.Hana:
The wire has to stick out from the capillary in order to discharge to form the ball. This wire came out from capillary is called tail, and the process of forming this tail is also called as tail bonding.
Miss Bondy:
How dose the tail formed?
Instructor Mr.Hana:
First of all, the wire is temporary connected with lead electrode by tail bonding. Next, only length required for Tail rises and only a capillary tears off the portion connected temporarily after that.It is verified by Video3 that the wire clamping circuit of the capillary upper part has opened and closed. With this movement of wire clamping enable to tear off the wire and also to rise the capillary by itself .
Miss Bondy:
Now that's all for bonding cycle isn't it? Thanks!
Dr.Yama:
Good job Mr. Hana, I am counting on you for the next lecture too.