System for No-Lead Integrated Circuit Packages Without Tape Frame
A system has a leadframe strip and a plurality of integrated circuit dies are each encapsulated in an encapsulant. The encapsulant has a plurality of first cuts and a plurality of second cuts therein. A fixture holds the package in said plurality of first cuts while said plurality of second cuts are made.
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This application is a Divisional of and claims priority to U.S. patent application Ser. No. 13/078,092, filed on Apr. 1, 2011 which claims priority to U.S. Provisional Application No. 61/227,269 filed on Jul. 21, 2009.
BACKGROUNDEmbodiments of the invention relates generally to no-lead integrated circuit (IC) packages and, more particularly, to singulation and strip testing of no-lead integrated circuit packages.
After packaging no-lead integrated circuits, for example QFN (Quad Flat No lead) and SON (Small Outline No Lead) type packages, conventional strip testing is advantageously employed. For example, with QFN, after attaching integrated circuit dies to die pads on a leadframe strip, and wire bonding the dies to the leads of the leadframe strip, blocks (rectangular arrays) of the dies and associated wire bonds are encapsulated in a suitable encapsulant material, for example a plastic mold compound.
The encapsulated leadframe strip 15 is mounted on a UV curable tape for singulation and strip testing.
The above-described use of the support tape 31 is somewhat delicate (and relatively costly) to implement. Movement of the encapsulated leadframe strip 15 while supported on the flexible tape 31 during sawing may contribute to generation of copper flakes and burrs that may short leads in the finished package. In addition, the movement can contribute to copper smearing onto the mold compound between leads. In addition, the temperature during strip testing must be suitably limited, because the UV curable tape typically does not withstand temperatures above 85° C. However, strip testing at temperatures above 85° C., and as high as 125° C., is often desirable because it simulates stresses on the die that may be occur during actual operation. After strip testing, the molded packages must be picked off the tape, without leaving any residual adhesive on the packages, and deposited in shipping tubes.
It is desirable in view of the foregoing to provide techniques for IC strip testing that avoid difficulties such as those described above with respect to the prior art.
Instead of using a UV curable tape with a tape frame and wafer dicing saw, exemplary embodiments of the present work place the encapsulated leadframe strip 15 on a saw table.
A saw (e.g., a simple table saw in some embodiments) is then used to make initial N/S and E/W cuts at, for example, generally the same locations as the cuts described above with respect to
After strip testing, the encapsulated leadframe strip is placed on a saw table (see, e.g., 82 in
In some embodiments, the table used for the second, singulation sawing operation is formed with a protruding portion that aligns spatially with the pattern of N/S and E/W partial cuts of
As also shown in
Various embodiments use various cutting technologies to make the aforementioned singulation cuts through the residual encapsulant layer 71. Examples include a laser, a water jet, or any other suitable cutting technology. Some embodiments make the partial cuts with a saw blade optimized for cutting encapsulant and metal, and make the singulation cuts with a saw blade optimized for cutting encapsulant.
Before performing strip testing, some embodiments treat the partially sawn encapsulated leadframe strip chemically, for electroless plating of NiPdAu, or for applying organic solderability preservative (OSP), to coat the edges of the metal leads that are exposed by the partial cuts or for removing metallic burrs or smears. The coating material is advantageous for corrosion prevention or for solder wetting of the exposed metal. This coating option is indicated in
Because the partial cuts and the singulation cuts are made with the encapsulated leadframe strip supported on respective saw tables, the encapsulated leadframe strip remains stabilized during the sawing operations.
copper flakes and burrs and copper smearing onto the encapsulant may be avoided because the strip is rigidly stabilized during the sawing operation, for consistent and clean sawing. The stability of the strip during sawing also provides enhanced size uniformity among the die packages 91. Thus, for example, some embodiments produce QFN packages as small as 2×2 mm, or even 1×1 mm, with a high degree of package size uniformity. Some embodiments use the saw table 61 for both sawing operations. Some embodiments use the saw table 82 for both sawing operations.
Although exemplary embodiments of the present work have been described above in detail, this does not limit the scope of the work, which can be practiced in a variety of embodiments.
Claims
1. A system comprising:
- a leadframe strip;
- a plurality of integrated circuit dies mounted on said leadframe strip each die electrically coupled to said leadframe strip;
- an encapsulatant encapsulating said leadframe strip and said plurality of integrated circuit dies; said encapsulant having a plurality of first cuts and a plurality of second cuts therein;
- a fixture having a protruding portion that is received in said plurality of first cuts while said plurality of second cuts are made.
2. The system of claim 1, wherein said second cuts are aligned with said first cuts and separate the encapsulated integrated circuit dies from one another.
3. The system of claim 1, wherein said fixture having vacuum ports to stabilize said encapsulated integrated circuit dies on said fixture.
4. The system of claim 2, wherein the separate, encapsulated integrated circuit dies are Quad Flat No lead (QFN) packages.
5. The system of claim 1, further comprising:
- a coating material on portions of said leadframe exposed by said plurality of first cuts and said plurality of second cuts.
Type: Application
Filed: Sep 30, 2013
Publication Date: May 22, 2014
Applicant: Texas Instruments Incorporated (Dallas, TX)
Inventor: Donald C. Abbott (Norton, MA)
Application Number: 14/041,878