COB (known as Chip-on-Board) is semi-conductor assembly technology where micro-chip also known as die is electrically interconnected instead of using traditional assembly process or individual IC packaging on the final product board. The general term meaning of this technology is direct chip attachment also refereeing to DCA. In DCA many kinds are available as substrate in form of ceramic glass or ceramic substrate which has substances of excellent dielectric and thermal property. It is also available in form of flex substrate, which exhibits bendable ability. Other names are known as COG (chip-on-glass) or COF (chip-on-flex).
COB process consists of three main categories to perform when manufacturing the Chip-on-Board. The first process is 'die mount or die attach', the second is 'wire bonding' and lastly 'the encapsulation of die wires'. In many COB assembly technology, FCOB(flip-chip-on-board) have chips facing downward on the board and does not require wire bonding which employs chip which the bond pads are pop up and it connects directly to pads on the board. It is necessary to underfill flip-chip on active surface to protect bumps from chemical and thermo-mechanical damage.
In context of COB manufacturing process,
1) 'die attach' consists of applying die attach holding to board or substrate mounting chip or die over die attach materials. 2) For wire bonding, thermosonic (Au or Cu) ball bending and ultrasonic (Al) wedge bending are used to connect wires between die and substrate. 3) Last part the encapsulation is done dispensing chemical liquid (usually epoxy) over die and wires. Die and bond wires are encapsulated to protect chemical and mechanical damage.
The advantages of COB include:
Better performance due to deceased interconnection between length and resistance.
Better protection against reverse engineering;
Reduced space and cost;
Shorter time to the market.
Higher reliability with better heat dispatch and small number of solder joint.
Improved output efficiency of LED lighting
Avoid photonic absorption and scattering over the pocket wall
LED Backlight for LCD TV
LED Front light for E-Book
Agriculture & Horticulture Lighting
Street & Parking Lot Lighting
Statement: This post is only the personal view of the author and does not represent the opinions of ALLPCB.com.