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Method for metrology for stickiness measurement on uBGA units

IP.com Disclosure Number: IPCOM000005403D
Publication Date: 2001-Sep-25
Document File: 3 page(s) / 55K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for metrology for stickiness measurement on uBGA units. Benefits include a repeatable, reproducible measurement and reduced surface contamination.

This text was extracted from a WORD97 document.
This is the abbreviated version, containing approximately 63% of the total text.

19671

Method for metrology for stickiness measurement on uBGA units

Disclosed is a method for metrology for stickiness measurement on uBGA units. Benefits include a repeatable, reproducible measurement and reduced surface contamination.

Background

A uBGA package is a chip-scale package mainly used for Flash memory devices. The uBGA package has two narrow windows found on the short ends of the unit (see Figure 1). Through these windows, the ends of the copper (Cu) traces can be seen but are protected from complete exposure to the surroundings by a layer of encapsulant material. In some cases, this encapsulant material sticks on the surface of the carrier tape used to package the uBGA units for the customer. Some units have sticky encapsulant materials and some do not. Sticky material hampers the pick-and-place process at the customer assembly lines.

The conventional method to test whether or not a unit sticks to the carrier tape is the flip-over method. The units to be tested are placed on a carrier tape. It is then turned over. The units that fall off within 10 seconds are considered not sticky. The units that remain on the reel are considered sticky.

This method is subjective, not reproducible, and unreliable. Specifically, the conventional method has the following disadvantages:

• Stickiness depends on how much force is exerted on the units when placed on the carrier tape, and the amount force is difficult to keep consistent

• The flip over action is not repeatable or reproducible

• Identification of sticky and not sticky is a matter of judgment and may be inconsistent

• Surface contamination occurs on the units after the flip-over, which limits further material testing and does not provide a quantitative measurement of the degree of stickiness in the units

The carrier tape is a polyimide tab tape with eutectic solder balls (63% Sn and 37% Pb). A thermosonic lead bond is used for the interconnection between the die to polyimide tape. A protective silicone elastomer compound between the die and polyimide tape absorbs stresses due to the coefficient of thermal expansion (CTE) mismatch.

Bond-pull equipment is conventionally used for making wire pull tests to measure the strength of the lead bonds on devices.

Description

The disclosed method quantifies the degree of stickiness of uBGA units with respect to the carrier tape. It makes use of the bond-pull equipment, a fabricated hook, a 50-g weight, a thin double-sided adhesive tape, a flat material at least 1-inch high, and uBGA units still on the carrier tape.

The method consists of the following steps:

1. Pieces of the double-sided adhesive tape on the flat material hold the carrier tape containing the units.

2. A piece of adhesive tape is placed under each well of the carrier tape, avoiding the hole at the center of the well (see Figure 2).

3. A 50-g ...