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Method for the controlled redeposition of laser-ablated material to form a thin protective layer over exposed metal

IP.com Disclosure Number: IPCOM000007802D
Publication Date: 2002-Apr-24
Document File: 5 page(s) / 931K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for the controlled redeposition of laser-ablated material to form a thin protective layer over exposed metal. Benefits include improved reliability and improved part tracking.

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Method for the controlled redeposition of laser-ablated material to form a thin protective layer over exposed metal

Disclosed is a method for the controlled redeposition of laser-ablated material to form a thin protective layer over exposed metal. Benefits include improved reliability and improved part tracking.

Background

              As package power increases, heat removal becomes more important in package design. Conventional heatsink designs completely cover the package topside, including the integrated heat spreader (IHS). The package marking inscribed on the IHS is no longer visible after heatsink attachment. Product manufacturing personnel, field service engineers, and major original equipment manufacturers (OEMs) pre-attach the heatsink before placing the CPU package on the motherboard. With the package mark covered by the heatsink, a new mark location is needed. The requirements are a permanent human-readable mark containing the finished process order (FPO) number, s-spec number, and serial number. The only part of the package visible after heatsink attachment is the pin side of the interposer. The mark is applied through the interposer solder resist to a copper plane in the interposer by laser etching (see Figure 1).

              Conventional solutions include paper labels applied with adhesive to the top of the pre-attached heatsink and the use of ink swatches, ink printing, and human markings on the top of the heatsink (see Figure 2).

General description

              Disclosed is a method of laser marking packages that enables the laser-ablated material to be redeposited on the laser-exposed copper (see Figure 3). The thin layer of redeposited material protects the exposed copper and reduces the levels of oxidation that forms over the life of the product.

              Key elements include:

§         Controlled laser power

§         Wavelength selected to ablate organic material and not etch metal

§         Works for human readable identification marks, 2D matrix marks, and barcodes

§         Laser-ablated materials, such as solder resist material

§         Marking anywhere on package where no active circuitry exists (Figure 4)

§         Redeposition of transparent corrosion resistant layer

 


Advantages

              Advantages of the disclosed method include:

§         Enables reuse of existing space

§         Does not increase cost

§         Addresses customer needs by providing a method for tracking of parts

§         Is a human-readable solution

§         Reduces the reliability risk as compared to exposed Cu mark with no redeposition of laser-ablated material

Detailed description

              The disclosed method can be demonstrated to work successfully. Reliability tests are performed on two test vehicles: completely assembled test vehicles (TV) and bare product interposers. Initially, the intent was to perform electrical tests and visual inspection on both TVs. However, electrical tests could not be performed on these interposers because automated testing required isolation of the pin access to the core power (VDD) plane, which was not possible.

              Two groups of 120 interposers (240 units tot...