Chemical and Electrochemical Separating

Lecture Video

First,

Remember metallic bonds.

Metals cations love to be around e-

Remember Redox Reactions

OIL (oxidation is loss of electrons)

RIG (reduction is gain of electrons)

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Chemical Machining

Chemical Machining

Machining process that works by dissolving material.

For example: zinc can be oxidized by hydrochloric acid. This forms zinc chloride and hydrogen:

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Masteretching.com

Chemical Milling

Typical Sequence

1. Material is prepared for masking
2. Mask is applied
3. Workpiece is exposed to etchant
4. Work is rinsed, mask is removed
1. Manually
2. Mechanically
3. Chemically
5. Work is re-washed and dried

Note: In chemical blanking, the part is cut completely through.

Masks

Can be applied by

• Cut and Peel
• Screen Printed

Desirable properties of maskants

• Durable enough to withstand handling
• Inert to chemical etchant
• Able to withstand heat of etching
• Adhere to work
• Scribe easily
• Removable

Photoresist Masks

Make the process "photochemical machining"

Makant is usually spin coated on the surface.

Masks are selectively exposed to UV light.

via. phototool (transparency)

Masks can be

• positive development
• maskant becomes more soluble after exposure
• negative development
• maskant become less soluble after exposure

Photochemical Machining

Photoresist is applied to the substrate

A Phototool is Applied over the Resist

Positive Development shown

Exposure

A Latent Image is Created

The Resist is Developed

Undeveloped Resist is Washed Away

The Exposed Areas are Etched Away

Finished Workpiece

Photochemical Etching (video)

On Quiz

Photochemical Etching (video)

On Quiz

Maskless DLP PCB Lithography

Etchants

Can be

• Acidic
• Alkaline
• Gaseous or liquid

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Advantages of CH Milling

• Process is relatively simple
• Does not require highly skilled labor
• Induces no stress or cold working in the metal
• Can be applied to almost any metal
• Large areas
• Virtually unlimited shape
• Thin sections

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Disadvantages of CH Milling

• Requires the handling of dangerous chemicals
• Disposal of potentially harmful byproducts
• Metal removal rate is slow

Defects in CH Milling

• Overhang: deep cuts with improper agitation
• Islands: isolated high spots from dirt, residual maskant, or work material inhomogeneity
• Dishing: thinning in center due to improper agitation or stacking of parts in tank.

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Electrochemical Machining

Used anodic dissolution

• Proportional to the current

ECM Advantages

• Can machine 3D shapes
• No tool wear, repeatable production
• No thermal damage (no HAZ)
• High surface quality
• Low labor requirements
• Burr Free

ECM Disadvantages

• Can only cut conductive materials
• Corrosive electrolytes can damage equipment
• Tends to lower endurance limit
• Slow metal removal rates
• High power requirements
• Parts must be post cleaned and oiled
• Tool and part can be damaged by accidental arcing

Electrochemical Machining (video)

On Quiz

IC Manufacturing

See how a computer works

On Quiz

IC Packaging

• Serves to distribute electronic signals and power
• Provides mechanical interfacing to test equipment and printed circuit boards (PCBs)
• Protect the delicate circuitry from mechanical stresses and electrostatic discharge during handling and in corrosive environments
• Dissipate heat generated in the circuits

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http://commons.wikimedia.org/wiki/File:DIP8,_NE555,_%28shaded,_isometric%29.svg

Types of Packaging

Through-hole/socket

• Dual In-Line Package (DIP)

Surface Mount Technology

• SMD
• Ball Grid Array (BGA)

Bare Die (no packaging)

http://en.wikipedia.org/wiki/File:Kl_Intel_Pentium_MMX_embedded_BGA_Bottom.jpg

IC Mounting Methods

Wire Bonding

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IC Mounting Methods

Flip Chip

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About thermosonic bonding