Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1998-11-13
2001-05-29
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S316000, C430S318000
Reexamination Certificate
active
06238845
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to lead frames used with semiconductor devices, and more particularly to a method of forming lead frames, with fine pitched leads, that utilizes a two step etching and support of the lead frame during the second etching step.
BACKGROUND OF THE INVENTION
Semiconductor devices are being developed to including an increasing number of components which also increases the required number of input/output leads. This increase in input/output leads has required the development of finer pitch lead tips on the lead frame.
The prior art process of making lead frames by etching utilizes a solid metal strip that is laminated on both sides with a photoresist material. Both sides of the photoresist material is exposed to a light though a pattern that defines the lead frame configuration. The photoresist is then developed to remove photoresist in areas that are to be etched to remove the unwanted metal from the metal strip.
The laminated metal strip with the patterned photoresist is then etched to define the metal lead frame. After the etch process, the leads of the lead frame are defined and are separate from one another. The etched leads are subject to damage during the remaining lead frame formation process.
After etching, the photoresist is striped or removed from the lead frame. The lead frame is then plated. Wire bond contact areas may be electroplated.
After plating, the leads of the lead frame are taped to hold them in their respective positions. The lead frames, which generally are formed in continuous strips, are then cut to length, having one or more lead frames on a stip.
The problems that exist with fine pitch leads on the lead frame has been addressed in U.S. Pat. No. 5,454,905, where the leads of the lead frame have two different thicknesses. The outer portion of the lead frame lead has a thickness greater than the inner portion adjacent to the semiconductor die. The inner portions of the lead frame leads have been etched to a less thickness than the outer portions of the lead frame leads.
SUMMARY OF THE INVENTION
The invention is a method for making a lead frame having fine pitched lead frame leads. A first side of the lead frame material is etched to form the lead frame and define the lead frame leads and die pad, but the etch process does not etch completely through the lead frame material. The partially etched first side is then covered with a tape. The second side of the lead fame material is then etched to complete the lead frame. The lead frame may then be plated.
In a second embodiment, the etched first side is covered with a photoresist layer, and the second is covered with photoresist and then etched to form the lead frame.
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Kelleher Harold T.
Lokhorst Gijsbert Willem
Moehle Paul R.
Brady III Wade James
Holmbo Dwight N.
Huff Mark F.
Mohamedulla Saleha R.
Telecky , Jr. Frederick J.
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