Lead Frames or Leadframes

Lead Frames

The lead frame, or leadframe, is the 'skeleton' of the IC package, providing mechanical support to the die during its assembly into a finished product. It consists of a die paddle, to which the die is attached, and leads, which serve as the means for external electrical connection to the outside world. The die is connected to the leads by wires through wirebonding or by tape automated bonds.

Plastic package lead frames are made of alloys that meet the following critical properties: good adherence to the molding compound, a coefficient of thermal expansion as close as possible to those of the die and the molding compound, high strength, good formability, and high electrical and thermal conductivities. Alloy42 is an example of such an alloy.

Fig. 1. Examples of Leadframes

Lead frames are constructed from flat sheet metal either by stamping or etching. Stamping is a highly-automated mechanical process that employs die and punch sets to progressively achieve the intended lead frame structure through a series of stamping/punching steps.

Etching consists of selectively covering the sheet metal with photoresist in accordance with the pattern of the lead frame. The sheet metal is then exposed to chemical etchants that remove areas not covered by photoresist. After the etching process, the 'etched' frames are singulated into strips.

After stamping or etching, the lead frame is then finished with cleaning, silver-plating, taping and downsetting steps. Silver-plating is done on the bonding fingers and die pad to improve wirebond and die attach quality. Taping consists of putting a lead lock tape over the leads to prevent lead deformation, while downsetting consists of pushing the die paddle down relative to the bonding fingers in compliance with standard industry requirements.

The lead frames are then inspected before being packed for shipment to the customer.

Examples of vendors of lead frames are QPL, DCI, and Olin Brass.

Table 1. QPL Etched Leadframe Open Tool Partial List

LEADCOUNT	DESCRIPTION	DRAWING NO.
28L	300X300 PDIP (.600")	QPL-28-PDIP-0016
48L	350X350 PDIP (.600")	QPL-48-PDIP-0006
84L	360X360 PLCC	QPL-84-PLCC-0018
100L	290X290 QFP (14X20)	QPL-100-QFP-0016
100L	410X410 QFP (14X20)	QPL-100-QFP-0024
18L	160X200 SOIC DUAL (.300")	QPL-18-SOIC-0005
18L	140X170 SOIC DUAL (.300")	QPL-18-SOIC-0006
20L	180X220 SOIC DUAL (.300")	QPL-20-SOIC-0010
20L	180X260 SOIC DUAL (.300")	QPL-20-SOIC-0012
28L	170X170 SOIC DUAL (.300")	QPL-28-SOIC-0017
28L	195X330 SOIC DUAL (.300")	QPL-28-SOIC-0056
20L	96X140 SSOP DUAL (.150")	QPL-20-SSOP-0002
24L	96X140 SSOP DUAL (.150")	QPL-24-SSOP-0002

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