Whisker-free lead frames

a lead frame and whisker technology, applied in the field of tin containing interconnects, can solve problems such as the potential to produce mechanical instabilities, and achieve the effect of reducing the proclivity to induce mechanical instabilities

Inactive Publication Date: 2006-03-30
AGERE SYST INC +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0008] The interaction between the tin of the solder and the copper from any of the solder pad metal interfaces (die, substrate, or board) has the potential to produce mechanical instabilities with concomitant reliability issues often characterized by very non-planar interfaces. Through the use of nickel in the solder in the range of 1 to 12 weight percent relativ

Problems solved by technology

Surprisingly it has been found that tin whiskers are present even after soldering with materials having been subjected to soldering temperatures above 232° C. Thus the issues associated with such whiskers remain with lead-free solders.
The interaction be

Method used

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example

[0019] A 0.25 um thick nickel layer was electroplated onto a copper lead frame. Subsequently a 3 um thick tin layer was electroplated onto the nickel layer. On a weight percentage basis the sample contains approximately 4% nickel and 96% tin. The device was then subjected to a 150° C. 1 hour anneal. Finally the device was subjected to a typical solder reflow process with a peak temperature of 260° C. The time the device was at 260° C. was approximately 18 seconds. A secondary electron image was taken from a focused ion beam cross section of the sample. As shown in FIG. 6, the entire tin layer is converted into a planar nickel / copper / tin intermetallic layer 61 on the copper lead 62. The platinum layer 63 was deposited onto the sample prior to focused ion beam cutting and acts as a reference that defines the surface of the tin / Ni / Cu layer.

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Abstract

The electrical and mechanical properties of structures such as lead frames and other electrical/electronic devices containing, during processing, copper/tin interfaces are improved by introduction of nickel to such interface. Typically, a weight percentage of nickel to tin in the range 1 to 12 weight percent yields upon melting of the tin, an intermetallic compound with essentially no occluded, unbound tin. Thus undesirable anomalous structures such as tin needles and substantially non-planar interface compositions are avoided. Advantageously a nickel/tin/copper intermetallic interface that is substantially planar is formed in the substantial absence of needle-like tin structures.

Description

TECHNICAL FIELD [0001] This invention relates to tin containing interconnects for electronic and electrical devices and in particular to tin containing interconnects that avoid formation of tin whiskers. BACKGROUND OF THE INVENTION [0002] For electrical and electronic devices, typically electrical connections are made through the expedient of a lead frame or other copper containing structures. For example, in the fabrication of integrated circuits, a silicon body having electronic circuitry is connected to a metal e.g. copper, lead frame such as shown in FIG. 1 at 2 with the chip positioned at 3 and connections between bonding pads on the chip and the lead frame shown at 4. After the chip is bonded to the lead frame, the chip is encapsulated typically in a polymer composition. The strip, 6, in FIG. 1 is removed from the lead frame in a process generally denominated trimming. Thus, after trimming, the individual leads, 7, are no longer mechanically connected on one end. The leads are...

Claims

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Application Information

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IPC IPC(8): B32B15/00B32B15/01
CPCB32B15/01C22C13/00C23C26/02H05K3/244H05K3/3463Y10S428/941Y10T29/49121Y10T428/12708Y10T428/12722Y10T428/12493Y10S428/929Y10T428/12715
Inventor HOOGHAN, KULTARANSINGH N.OSENBACH, JOHN W.POTTEIGER, BRIAN DALERUENGSINSUB, POOPASHOOK, RICHARD L.SURATKAR, PRAKASHVACCARO, BRIAN T.
Owner AGERE SYST INC
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