JPH03280456A - Lead frame used for semiconductor device - Google Patents

Abstract

PURPOSE:To hold down the diffusion rate of Sn so as to prevent an Sn or a solder plating layer from deteriorating in adhesion or separating by a method wherein a part of a first-surface treated layer and all the third surface-treated layer are coated with resin, and the first-surface treated layer is interposed between a second surface-treated layer and a resin sealed region. CONSTITUTION:All outer lead 4 and a part of an inner lead 3 located inside a dam bar 5 are subjected to an Ni-plating treatment to form a first surface- treated layer 7. In succession, the surface of a region which is located outside of a resin sealed region and does not include the outer lead 4 is coated with a tin or a solder plating film to form a second surface-treated layer 8. Furthermore, a device mounting pad 2 and a wire bonding area 10 located at the tip of the inner lead 3 are subjected to a base partial plating treatment, which is coated with a gold or a tin plating layer to form a third surface-treated layer 9. In the lead frame 1 provided with the first third treated layer, 7-9, a semiconductor device 13 is fixed onto the device mounting pad 2, the bonding pad of the semiconductor device 13 is connected to the third surface-treated layer 9 located at the tip of the inner lead 3 with a wire 14 to constitute an electrically conductive circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lead frame having a plurality of surface treatment layers in which required portions of the lead frame are coated with plating layers of different metals.

[Conventional technology]

In a typical semiconductor device, a semiconductor element is fixed to the element mounting pad of a lead frame via a surface treatment layer, and the bonding pad of the semiconductor element and the inner lead of the lead frame are connected with a wire to form an electrically conductive circuit. It is manufactured by forming these and then sealing them with resin.

As shown in FIG. 3, a lead frame 31 used in a semiconductor device has an element mounting pad 3 on which a semiconductor element is mounted.
2, inner leads 33 whose tips are arranged radially so as to surround the element mounting pad 32, a dam bar 35 which extends in a direction perpendicular to these inner leads 33 and integrally supports the inner leads 33, and this dam bar. The outer lead 34 is arranged to be connected to each inner lead 33 via a wire 35, and a support pad 36 supports the element mounting pad 32.

In this lead frame 31, the tip portions of the inner leads 33 are subjected to a surface treatment layer such as gold plating or silver plating. These surface treatment layers are performed in a step after resin sealing.

Applying a plating layer in this way complicates the manufacturing process, which is one of the obstacles in terms of cost. In addition, corrosive components contained in the plating solution (CI-, SO,-, F-, etc.) may enter through the gap between the resin seal and the lead, corrode the bonding wire, and cause disconnection. It is also a factor in the decline in sexuality.

In order to solve this problem, a structure as shown in FIG. 4 has been conventionally adopted. This is a step before resin sealing, in which a surface treatment layer 37 such as gold or silver plating is formed on the tip of the element mounting pad 32 and the inner lead 33 of the lead frame 31, and then the outer lead 34 and the inner lead 33 are coated with a surface treatment layer 37. A region including a part of is covered with a surface treatment layer 38 of solder plating. When the lead frame 31 subjected to such surface treatment is used, the surface treatment layer 38 is included in the sealing area with the resin 39 and is manufactured into a product.

[Problem to be solved by the invention]

However, the tin or tin alloy of the surface treatment layer 38 tends to form a thick porous oxide film, and the tin oxide film has poor adhesion to the metal base and easily peels off.

Therefore, if the surface treatment layer 38 of solder plating is covered with the resin 39, a gap may be created between the surface treatment layer 38 and the resin 39 due to such a peeling phenomenon. Therefore, there is a risk that moisture, corrosive components, etc. may enter through this gap, reducing the reliability of the semiconductor device.

On the other hand, some devices apply a surface treatment layer of solder plating to the outside of the resin sealing area. However, when this is used, the metal base of the lead frame material is exposed between the surface treatment layer and the resin.

The metal base of the lead frame is Cu-based alloy or 42%
Ni alloys are mainly used, but Cu-based alloys tend to form a CuO oxide film in the atmosphere, and 42
%Ni alloy has a large difference in thermal expansion coefficient from that of the resin, and also has the problem of lacking long-term reliability because it rusts like Fed and Fe20s.

Further, other types of lead frames include those in which silver or solder plating is directly applied on copper or copper alloy, or in which tin or solder plating is applied to a layer on top of copper plating. In this case, due to the long-term use environment, mutual diffusion of Sn and Cu occurs, and a large number of pores are generated at the interface between the tin or solder plating layer and the base plating layer. Therefore, the adhesion of the tin or solder plating layer deteriorates, and the tin or solder plating layer easily peels off due to the Kirkendall effect.

Therefore, an object of the present invention is to provide a high quality lead frame by eliminating all the conventional drawbacks and forming a surface treatment layer with excellent stability and reliability.

[Means to solve the problem]

In the lead frame of the present invention, the inner lead including the base end side of the outer lead and outside the wire bonding area and the back surface of the element mounting pad of the semiconductor element are coated with Ni or a Ni alloy, and a first surface treatment layer is formed. form,
The outer lead outside the resin sealing area is made of Sn or S.
n alloy to form a second surface treatment layer, and further coat the mounting surface side of the element mounting pad and the wire bonding area of the inner lead with 80 or 8g or Pd or an alloy thereof to form a third surface treatment layer. It is characterized by forming a layer.

[Effect]

When a semiconductor device is assembled using the lead frame of the present invention, the boundary line between the resin-sealed region and the non-sealed region runs on the first surface treatment layer. On the other hand, during high-temperature treatment in semiconductor device assembly processes such as mounting of semiconductor elements and wire bonding, the surface of the Ni or Ni-Sn alloy plating layer of the first surface treatment layer is oxidized to a thickness of several hundred nanometers. forms an oxide film. This oxide film is estimated to be NiO, and its adhesion to the resin is far superior to that of conventional 42% Ni-based alloys, cobalt, copper, copper alloys, etc. and resins. Therefore, moisture and corrosive components are prevented from entering between the resin and the lead frame after resin sealing.

In addition, since the first surface treatment layer is interposed between the second surface treatment layer of the outer lead and the resin, intermetallic compounds such as Sn and Ni (Nis Sn) are formed during the assembly process and usage environment of the semiconductor device. This prevents Sn from diffusing into the lead frame.

〔Example〕

FIG. 1 is a plan view of the lead frame of the present invention, and FIG. 2 is a sectional view taken along the line I--I in FIG. 1 after plating.

As in the conventional example, the lead frame 1 has device mounting pads 2 . Inner lead 3. outer lead 4
．． The dam bar 5 and the support part 6 of the element mounting pad 2 are formed by press working.

The lead frame 1 after this press processing is sent to a plating process, and first the entire outer lead 4 and the dam bar 5 are plated.
A part of the inner lead 3 on the inner side is subjected to Ni plating treatment to form a first surface treatment layer 7 . This first surface treatment layer 7 may be made of a Ni-Sn alloy, and has a thickness of about 1 μm.

Next, a second surface treatment layer 8 is formed by covering the front surface of the resin-sealed area to the area outside the resin-sealed area and not including the outer leads 4 with tin or solder plating. The thickness of this second surface treatment layer 8 is approximately 1 to 2 μm.

Further, the element mounting pad 2 and the wire bonding area 10 at the tip of the inner lead 3 are partially plated with a base of about 1 μm, and then covered with a gold or silver plating layer to form a third surface treatment layer 9.

The copper base plating of the third surface treatment layer 9 may be applied to the front surface of the lead frame l, but the upper copper base plating layer of the third surface treatment layer 9 may be peeled off and dissolved by anodic electrolytic treatment in a CN solution. Remove.

Lead frame 1 provided with first to third surface treatment layers 7 to 9
As shown in FIG. 2, the semiconductor element 13 is fixed on the element mounting pad 2, and the bonding pad of the semiconductor element 13 and the third surface treatment layer 9 at the tip of the inner lead 3 are connected with a wire 14. to form an electrically conductive circuit.

Then, by integrating these semiconductor elements 13 and wires 14 and sealing the area within the resin sealing boundary line 11 with resin 12, a product is obtained.

Note that the surface treatment layer of the inner leads 3 and the element mounting pads 20 may be applied only to the tips of the inner leads 3. Also,
It is a matter of theory that the resin may be an inorganic material, and the surface treatment layer may be formed not only by plating but also by vapor deposition, cladding, or the like.

〔Effect of the invention〕

In the present invention, a part of the first surface treatment layer and the entire third surface treatment layer are coated with resin, and the first surface treatment layer is interposed between the second surface treatment layer and the resin sealing region. There is. Therefore, the diffusion rate of Sn is suppressed, and deterioration in adhesion and peeling of Sn or the solder plating layer can be prevented.

Furthermore, since the surface treatment layer covers the required portions of the lead frame before sealing with the resin, the adhesion of corrosive components due to impurities is reduced.

Therefore, the adhesion between the resin and the lead frame is good, and a highly stable and reliable semiconductor device can be obtained. Furthermore, compared to conventional manufacturing processes, the number of steps is reduced, making it advantageous in terms of cost.

[Brief explanation of drawings]

FIG. 1 is a plan view of the lead frame of the present invention, and FIG. 2 is an enlarged view of the lead frame and the thickness of the surface treatment layer.
A longitudinal sectional view taken along the line 1-1 in the figure, and FIGS. 3 and 4 show a conventional example. 1: Lead frame 2: Element mounting pad 3; Inner lead 4; Outer lead 5; Dam bar 6:
Support par 7: First surface treatment layer 8: Second surface treatment layer 9: Third surface treatment layer lO; Wire bonding area 11: Resin sealing region boundary line 12; Resin 13: Semiconductor element 14: Wire

Claims (1)

[Claims] 1. A first surface treatment layer is formed by coating the inner lead outside the wire bonding area and the back surface of the element mounting pad of the semiconductor element including up to the base end side of the outer lead with Ni or Ni alloy, and resin sealing. The outer lead outside the stop area is coated with Sn or a Sn alloy to form a second surface treatment layer, and the mounting surface side of the element mounting pad and the wire bonding area of the inner lead are coated with Au, Ag, Pd, or the like. A lead frame for use in a semiconductor device, characterized in that the lead frame is coated with an alloy to form a third surface treatment layer.