Effective method and whole process details of chip decap detection

Date：2021-11-11 13:40:00Views：8027

Chip decap, also known as chip unsealing or chip cap opening, is a common detection method for chip failure analysis. Usually, the data book can provide a lot of information about the chip. If you want to design reliable, low-power and high-performance chip products, you can't stay in the data book. You need to deeply study the internal working principle of the integrated circuit, the relationship between its manufacturing process and its performance, and have a certain ability to analyze the integrated circuit.

Chip packaging materials

A chip usually consists of the following structures:

1. Conductor rack. It is made of metal and used to connect silicon wafer and circuit board.

2. Plastic or ceramic shell. Made of plastic or ceramic, usually black or white, to protect silicon wafers.

3. Connecting wire between wafer and wire rack. It is composed of gold wire or aluminum wire, which is used to connect silicon wafer and conductor frame.

4. Silicon wafer. It is composed of high purity silicon, dopants and metals. It is the core component of integrated circuit.

5. Cooling base. Made of metal, the silicon wafer is glued to the heat dissipation base.

The packaging materials of various chips are stripped layer by layer by physical or chemical methods to realize the visual inspection and electrical test of the internal structure of the chip. Chip unsealing is an important means of chip failure analysis. The current chip unsealing methods include mechanical unsealing, acid etching unsealing and plasma unsealing.

Principle analysis:

The mechanical unsealing method uses a drill or cutter to remove the packaging material of the chip. This unsealing method has slow speed and poor controllability, and is not suitable for the chip with small structure size.

The principle of acid etching unsealing method is to etch the plastic sealing layer of the chip with an appropriate amount of strong acid. The waste liquid formed by acid etching unsealing method is easy to cause environmental pollution, and the unsealing process is not controllable.

Meaning of chip cover opening

Decap refers to opening the seal, also known as opening the cover and cap. It refers to the local corrosion of the fully encapsulated IC, so that the IC can be exposed, while maintaining the integrity of the chip function, and keeping die, bond pads, bond wires and even lead from damage, so as to prepare for the next chip failure analysis experiment and facilitate observation or other tests (such as FIB and Emmi). The function of decap is normal.

Chip cover opening range

Common package cob, BGA, QFP, QFN, sot, to, dip, BGA, cob ceramic, metal and other special packages.

Chip cover opening method

General include chemical, mechanical, laser and plasma decap. Now mostDecap laboratory can handle almost all IC packaging forms (COB, QFP, dip, sot, etc.) and wiring types (AU, Cu, Ag).

Under the action of hot concentrated nitric acid (98%) or concentrated sulfuric acid, the polymer resin is corroded into a low molecular compound easily soluble in acetone. Under the action of ultrasound, the low molecular compound is washed away to expose the surface of the chip.

Chip cover openingMethod 1: heat on the heating plate at a temperature of 100-150 degrees. Turn the front of the chip upward and suck a small amount of fuming nitric acid (concentration > 98%) with a straw. Drop it on the product surface. At this time, the resin surface has a chemical reaction and bubbles appear. Drop it again after the reaction stops. After dropping 5-10 drops continuously, clamp it with tweezers and put it into a beaker containing acetone. After cleaning in an ultrasonic cleaner for 2-5 minutes, take it out and drop it again. Repeat this until the chip is exposed, Finally, clean the chip surface repeatedly with clean acetone to ensure that there is no residue on the chip surface.

Chip cover openingMethod 2: Boil all products in 98% concentrated sulfuric acid at one time. This method is more suitable for the case of large quantity and only depending on whether the chip is broken. The disadvantage is that the operation is dangerous. Master the essentials.

Precautions for cover opening: all operations shall be carried out in the fume hood and acid proof gloves shall be worn. The more the product is opened, the less acid should be dropped and cleaned frequently to avoid excessive corrosion. During cleaning, the tweezers shall not touch the gold wire and chip surface to avoid scratching the chip and gold wire. According to the product or analysis requirements, some conductive adhesive under the chip shall be exposed after opening the cap, or the second point. In addition, in some cases, the open cap products shall be retested according to the row. At this time, first observe whether the gold wire on the chip is broken and collapsed under an 80x microscope. If not, scrape the black film on the pin with a blade and send it for measurement. Pay attention to control the opening temperature not too high.

Acid commonly used in analysis: concentrated sulfuric acid: This refers to 98% concentrated sulfuric acid, which has strong dehydration, water absorption and oxidation. When opening the cap, it is used to cook a large number of products at one time. Here, its dehydration and strong oxidation are used. Concentrated hydrochloric acid: refers to 37% (V / V) hydrochloric acid with strong volatility and oxidation. It is used to remove the aluminum layer on the chip in the analysis. Fuming nitric acid: refers to nitric acid with a concentration of 98% (V / V). To open the hat. It has strong volatility and oxidation, and is reddish brown due to the dissolution of NO2. Aqua regia: refers to the mixture of one volume of concentrated nitric acid and three volumes of concentrated hydrochloric acid. It is used to corrode gold ball in analysis because it is highly corrosive and can corrode gold.

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