Browse Prior Art Database

Post-Grind Sealant for Encapsulated Array Packaging©

IP.com Disclosure Number: IPCOM000031671D
Original Publication Date: 2004-Oct-04
Included in the Prior Art Database: 2004-Oct-04
Document File: 5 page(s) / 1M

Publishing Venue

Motorola

Related People

Bill Lytle: AUTHOR [+2]

Abstract

Some applications of encapsulated packages require thin geometries under 1mm. In some cases, especially packages that can be manufactured multiply in arrays, uniform thinning can be accomplished by mechanical lapping. Many package encapsulation materials such as mold compounds are composites of an epoxy and a filler used to impart specific properties to the composite. The fillers are typically refractory compounds such as silica or alumina. These filler particles are typically embedded in the polymer matrix after curing. The lapping or grinding action for thinning not only produces debris from the abrasion of the polymer matrix but also breaks up the filler particles as well. Undamaged particles below the abraded zone may also become dislodged and add to the particulate debris. Finally corrosive processes such as desmear used for deburring after via hole drilling attack the mold compound releasing more filler particles. This debris results in large source of particulates which will contaminate equipment and chemical tanks used in subsequent processing of the package arrays. The small size of some of the particles generated by grinding make them difficult to remove from device surface by mechanical processes due to Van der Waals forces. Even without attractive forces, extensive cleaning processes would be required at each step to remove newly dislodged particles to prevent them from being carried into the next process. The roughened surface is also not esthetically pleasing and is not conducive to marking by either laser or inking procedures.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 31% of the total text.

Post-Grind Sealant for Encapsulated Array Packaging

Bill Lytle and George Leal

Freescale Semiconductor Inc.

Some applications of encapsulated packages require thin geometries under 1mm. In some cases, especially packages that can be manufactured multiply in arrays, uniform thinning can be accomplished by mechanical lapping. Many package encapsulation materials such as mold compounds are composites of an epoxy and a filler used to impart specific properties to the composite. The fillers are typically refractory compounds  such as silica or alumina.  These filler particles are typically embedded in the polymer matrix after curing. The lapping or grinding action for thinning not only produces debris from the abrasion of the polymer matrix but also breaks up the filler particles as well. Undamaged particles below the abraded zone may also become dislodged and add to the particulate debris. Finally corrosive processes such as desmear used for deburring after via hole drilling attack the mold compound releasing more filler particles. This debris results in large source of particulates which will contaminate equipment and chemical tanks used in subsequent processing of the package arrays. The small size of some of the particles generated by grinding make them difficult to remove from device surface by mechanical processes due to Van der Waals forces. Even without attractive forces, extensive cleaning processes would be required at each step to remove newly dislodged particles to prevent them from being carried into the next process. The roughened surface is also not esthetically pleasing and is not conducive to marking by either laser or inking procedures.

We have proposed the use of selected coating materials to reseal the lapped surfaces to reseal after grinding to prevent process contamination and improve package integrity. The coating material must be nearly impervious to the chemicals used to process the package arrays and also mark able at the end of processing.

The following chemical processes were used for our investigation of potential coating materials and are typical of processes used in the manufacture of printed circuit board to prepare for through hole plating after via drilling. The coating being sought was required to pass the following sequential process treatment with limited visual damage at the end of the combined processes..

1)       Swelling: A water based solution of containing a glycol ether such as butyl carbitol and less than 1%  sodium hydroxide. Processing parameters of 15 minutes at 60ºC was used.

2)       Desmear: This step is uses a powerful oxidizer and dissolves a via slag and a thin layer of epoxy as well as.  The solution is composed of 61g/L potassium permanganate (KMnO4) and 32g/L NaOH. We used 15 minutes at 65° based on circuit board industry practice. This process is not only destructive to the filled epoxy but also leaves heavy residues of manganese dioxide (MnO2).

3)       Reduction:   A 10% solution of sulfuric acid c...