JPH02122660A - Plastic package - Google Patents

Abstract

PURPOSE:To eliminate tie-bar cutting process and solder bridge and to improve moisture resistance by composing the tie-bar for a lead frame of resin different from the mold sealing resin and containing the tie-bar in the package when the mold is sealed thereby eliminating the necessity of cutting tie-bar. CONSTITUTION:A tie-bar 1 is made by contacting resin having high melting point, e.g., a highly heat-resistant polyimide adhesion film, tightly with each lead and adhered to a lead frame having no lead frame such that it covers the lead vertically and horizontally. The highly heat-resistant polyimide adhesion film is adhered to the border of resin seal. Then bonding, molding (epoxy resin) and lead formation are carried out thus constituting a package. Since the highly heat-resistant adhesion film contacts with a lead at the border of resin seal, adhesion does not degrade and good moisture resistance is achieved. Furthermore, since the tie-bar is contained in a mold package, solder bridge can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plastic package using a lead frame, and more particularly to a multi-bin plastic package and a plastic package attached to a printed circuit board by performing a solder dip flow.

[Conventional technology]

Conventionally, the lead frame used for this type of plastic package has a structure as shown in Figure 3 (a), in which a chip is mounted and the leads are cut and separated after being sealed with resin (usually epoxy resin is used). Tie bar 1 at
′ is cut. Figure 3(b) shows the tie bar after it has been cut.

[Problem to be solved by the invention]

The resin used in the conventional plastic package mentioned above is epoxy resin, so when it is attached to a printed circuit board, the epoxy sealing resin will thermally deform when exposed to flow conditions and the lead frame will be damaged. This deteriorates the adhesion between the leads and the roots of the package, leading to moisture infiltration from the roots, resulting in a significant deterioration of moisture resistance.

Also, during assembly, the tie bars are cut as shown in Figure 3(b).
As shown in (d), each lead has a protrusion due to an error in the margin when cutting the tie bar, which causes a problem of solder bridging of each lead during solder dipping and reflow.

[Means to solve the problem]

In the plastic package of the present invention, the tie bars of the lead frame are made of a resin different from the resin for mold sealing, and the tie bars are housed within the package during mold sealing.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

In FIG. 1, (a) is a diagram of one embodiment of the lead frame used in the present invention, (b) is an enlarged cross-sectional view of a part of the tie bar, and (c) is a cross-sectional view of the package after assembly. It is.

In FIG. 1(a), the tie bar 1 is configured as a tie bar by closely adhering resin with a high melting point to each lead.
In this example, a highly heat-resistant polyimide adhesive film is used. ) Glue to the lead frame without a dipper so as to cover the top, bottom, left and right sides of the lead as shown in figure (b). At this time, the highly heat-resistant polyimide adhesive film is attached to the edge of the resin seal, as shown in Figure (c).

Next, a package is constructed by performing ponder mold encapsulation (epoxy resin) and lead molding.

As a result of the above, the following two features can be obtained.

1. When subjected to solder dip and reflow conditions, the epoxy resin tends to undergo thermal deformation, resulting in poor adhesion to the lead frame and moisture infiltration from the base of the lead, resulting in poor moisture resistance. However, since the highly heat-resistant polyimide adhesive film is in close contact with the leads at the edge of resin sealing, the adhesion is not deteriorated and the moisture resistance is good.

2. When assembling a plastic package, the usual method is to cut the tie bar 1' to make each lead independent, as can be seen from the lead frame in Figure 3 (a). As shown in Figure (b), a dieper cut mark 7 is formed on each lead. This protrusion often causes solder dips and solder bridges during reflow, but in the present invention, the tie bars are housed within the mold package, so the tie bars do not protrude to the outside, so solder bridges can be prevented.

FIG. 2 is a diagram of a second embodiment of the present invention, in which (a) is an enlarged sectional view of a part of the tie bar, and (b) is a diagram of a part of the lead frame.

In this example, the highly heat-resistant polyimide adhesive film used in Example 1 is used, but forming holes 9 between the leads and the film has the advantage of improving moisture resistance by further increasing the adhesion of the sealing resin.

〔Effect of the invention〕

As explained above, in the present invention, the tie bars of the lead frame are made of a resin different from the mold sealing resin, and the tie bars are stored in the package during mold sealing, so there is no need to cut the tie bars, so the tie bars can be cut. This has the effect of reducing the number of steps, preventing solder bridges, and improving moisture resistance.

[Brief explanation of drawings]

FIG. 1 is a diagram of an embodiment of the present invention, in which FIG. 1(a) is a lead frame, FIG. 1(b) is an enlarged view of a lead part,
FIG. 1(c) is a diagram of the package housed in the package, FIG. 2 is a diagram of Embodiment 2 of the present invention, FIG. 2(a) is an enlarged view of the lead part, and FIG. 2(b) is a diagram of the lead part. Figure 3, a diagram of a portion of the frame, is a diagram of a conventional plastic package.
Figure 3(a) is the lead frame, Figure 3(b) is the view after the tie bar is cut, Figure 3(c) is the view housed in the package, and Figure 3(d) is the view of the package from above. It is. 1... Tie bar of the present invention 1'... Conventional tie bar 2... Lead, 3...
Island, 4... Chip, 5... Bonding wire 6... Sealing resin, 7...
... Tie bar cut marks, 8... Package,
9...hole. Agent: Susumu Uchihara, patent attorney Figure 2 Figure 3

Claims (1)

[Claims] A plastic package using a lead frame, characterized in that the tie bars of the lead frame are made of a resin different from a resin for mold sealing, and the tie bars are housed within the package during mold sealing. .