JPH0138373B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a seam welding method, more specifically, to a seam welding method using a parallel movement type seam welding machine, when a welding electrode first contacts a lid on a package base and when it is removed. This invention relates to a method for preventing sparks from occurring when

(2) Technical background Seam welding is one method of attaching a lid to a semiconductor package cage. Figure 1 is a cross-sectional view of a semiconductor package (hereinafter simply referred to as a package), in which 1 is a package base, 2
is a seal frame brazed to the package base 1, 3 is a lid, 4 is a semiconductor chip, 5 is a wire for connecting the semiconductor chip 4, and 6 is connected to the wire 5 via a wiring layer in the package base 1. The outer leads are shown respectively.

The lid 3 is welded to the seal frame 2 by a seam welding machine, and the seam welding method when a parallel movement seam welding machine is used as the seam welding machine is shown in a plan view in Fig. 2. The package fixed to the non-contact jig is moved in the direction shown by the arrow in FIG.
(hereinafter simply referred to as electrodes), for example, 8 volts between
Approximately 140 to 180 amperes of power can be applied. The electrode 7 contacts the lid 3 made of Kovar or 42 alloy and moves in parallel, and the lid 3 is melted by the module heat generated at the contact area between the lid 3 and the seal frame 2, and the lid 3 is made of Kovar or alloy. Welded to the seal frame 2 made of 42.

When all the long sides of the lid 3 are welded and the welding electrode 7 is removed from the lid 3, the jig is turned 90 degrees as shown by the arrow in FIG. 2b to change the orientation of the package.

Next, as shown in FIG. 2c, the gap between the electrodes 7, 7 is widened, the package is moved in the direction of the arrow, and the short side of the lid 3 is welded to the seal frame 2.

Although the above steps can be carried out in air, they are carried out in a sealed chamber called a dry box to prevent oxidation.

The welding method described above is schematically shown in the front view of FIG.
When the first contact with the edge of the lid 3, the welding current
When the package cage is moved in the direction of the arrow and the electrode 7 reaches the opposite edge of the lid 3, the position is shown by the dotted line in the figure. When the electrode 7 is removed from this position, the welding current is turned OFF. .

(3) Prior Art and Problems When the welding electrode first contacts the lid and when it separates from the lid, the electrode 7 contacts only the edge of the lid 3, which limits the current path and generates sparks. The situation at that time is shown in Figure 4,
Sparks flying in the direction indicated by the arrows may cause the edge portions of the seal frame 2 and lid 3 to chip along the line 8. In that case, the lid 3 will be attached to the seal frame 2 by later welding.
Even if the chip is welded, the sealing of this chipped part is incomplete, and the sealed _N2 gas may leak from that part or moisture from the outside can enter the package, resulting in a reduction in the manufacturing yield of the semiconductor package and the quality of the product. Adversely affects reliability.

(4) Purpose of the Invention In view of the above-mentioned conventional problems, the present invention has been made to solve the above-mentioned problems in the conventional art. It is an object of the present invention to provide a seam welding method in which generation of sparks is prevented when contacting the edge portion and when separating from the lid.

(5) Structure of the Invention According to the present invention, a metal lid is placed on a seal frame attached to a semiconductor package base, and a pair of welding electrodes are brought into contact with two opposing sides of the lid. When seam welding is performed by moving the pair of welding electrodes while the pair of welding electrodes is still moving, the pair of welding electrodes are brought into contact with the lid while a low voltage is applied between the pair of welding electrodes, and then the voltage applied between the pair of welding electrodes is By providing a seam welding method characterized in that the voltage applied between the pair of welding electrodes is lowered to a low voltage and the pair of welding electrodes are separated from the lid. will be achieved.

(6) Embodiments of the Invention In order to solve the above-mentioned problems of the prior art, the inventor of the present application considered applying a slope current as shown by a rectangular wave in FIG. 5a and a sine wave in b. Figure 5, which plots time (T) on the horizontal axis and current (I) on the vertical axis, shows the waveform of the current flowing through the electrode 7. Around point A, when the welding electrode first contacts the lid, there is a spark. A weak current that cannot generate the welding is applied, and then the current necessary for welding is applied. Also, if the point at which the welding electrode separates from the lid is B, then just before it approaches B, the electrode value should be weakened to 0 to prevent sparking.
I'll go there too.

By passing such a slope current,
That is, the point A when the welding electrode first contacts the lid.
By suppressing the value of the current flowing through the electrode 7 to a weak value that does not generate sparks near the welding electrode and at the time B when the welding electrode separates from the lid, sparks when the electrode 7 contacts the edge of the lid 3 are reduced. It becomes possible to prevent the occurrence.

A slope current as described above is obtained by the apparatus shown in FIG. Jig 9 where the package cage is fixed
meshes with axis 10 of the normal XY drive system, and axis 1
0 can be driven by a motor 11 in the left and right direction (X direction) as seen in the figure. The shaft 10 is connected to an encoder 12 via a motor 11, and the movement of the shaft 10 in the X direction, and hence the movement of the jig 9 in the X direction, is transmitted to the encoder 12, which is detected by a photo sensor 13, The result is sent as a signal to the power supply 14, which controls the current flowing to the electrode 7. If the length of the lid 3 in the X direction is measured in advance, the current value will be automatically controlled until the electrode contacts and separates from the lid. Regarding movement in the Y direction, since the direction of the package is simply changed by 90 degrees, the current value and control can be controlled using the same principle as above, so Figure 2 a
In the seam welding shown in and c, it is possible to prevent the generation of sparks when the electrode contacts and separates from the lid.

(7) Effects of the Invention As explained in detail above, according to the method of the present invention, in seam welding for welding a lid to a semiconductor device using the parallel movement method, when the electrode contacts the edge of the lid, that is, when the current is This prevents the generation of sparks when turning on and off, which is highly effective in improving the manufacturing yield and reliability of semiconductor packages.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a semiconductor package, FIG. 2 is a plan view of the semiconductor package to explain seam welding using the parallel movement method, and FIG. 3 is a front view showing the arrangement of electrodes and semiconductor packages in seam welding. FIG. 4 is an enlarged view of the lid and sealing frame of the semiconductor package shown in FIG. 1, FIG. 5 is a diagram of the slope current used in the method of the present invention, and FIG. 6 is the arrangement of equipment for carrying out the method of the present invention. It is a diagram. DESCRIPTION OF SYMBOLS 1...Package base, 2...Seal frame, 3...Lid, 4...Semiconductor chip, 5...Wire, 6...Outer lead, 7...Welding electrode, 8...
Missing line, 9... Jig, 10... Axis, 11... Motor, 12... Photo sensor, 13... Encoder, 14... Electrode.

Claims (1)

[Claims] 1. When performing seam welding by placing a metal lid on a seal frame attached to a semiconductor package base and moving a pair of welding electrodes while keeping them in contact with two opposing sides of the lid, After bringing the pair of welding electrodes into contact with the lid with a low voltage applied between the electrodes, welding is performed by increasing the voltage applied between the pair of welding electrodes, and applying it between the pair of welding electrodes. A seam welding method characterized in that the pair of welding electrodes is separated from the lid while the voltage is lowered to a low voltage.