Electronics Manufacturing By Ed Red E lectronics manufacturing comprises 1/3 of all manufacturing in the world! Objectives Review basic processes used to make IC’s. Review basic processes used to make circuit boards. Review methods and equipment used to assemble circuit boards.
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Electronics ManufacturingByEd Red
Electronics manufacturing comprises 1/3 of all manufacturing in the world!
An ingot is sliced into wafers of thickness about 0.02 inches, followed by polishing and edge rounding.
Procedures are repeated until you build the desired integrated circuit features that you want..these are called dies.
A crystal growing process is used to grow single crystal ingots of silicon of diameters approaching 12 inches and lengths to 10 ft.
IC production process is a planar process consisting of region-specific layering or de-layering processes to constitute the many microscopic electronic devices spread across the wafer surface.
The process begins by producing from quartzite (SiO2) an electronic-grade silicon (EGS) with little impurity. The process involves mixing of elements into a furnace, grinding of the resulting alloy, and further chemical reaction with the powder to produce the pure silicon.
Transfer of the IC to an electronics component is called packaging.
An IC is comprised of millions of electronic devices such as diodes, resistors, and transistors, and is packaged in a plastic enclosed body as a through hole or surface mount device with leads (legs) for electrical interfacing to circuit boards.
Two materials are typically used to encapsulate the IC: 1) plastics with no hermetic sealing; and 2) ceramics with hermetic sealing (e.g., alumina, Al2O3).
The number of I/O terminals is a function of the number of devices on the IC. The dependency between the two is established by Rent’s Rule (around 1960):
nio = C ncm
where nio is the number of I/O leads and nc is the number of circuits on the IC, usually taken as the number of logic gates. Some common values for C and m are:
Microprocessor C = 4.5 m = 0.5
Static memory C = 6.0 m = 0.12
Lead spacing is about 20 mils
Photolithographic process applied to a silicon wafer:(1) prepare surface; (2) apply photoresist; (3) soft bake; (4) align mask and expose; (5) develop resist; (6) hard bake; (7) etch; (8) strip resist.
IC fabrication sequence: (1) Si3N4 mask is deposited by CVD on Si substrate; (2) SiO2is grown by thermal oxidation in unmasked regions; (3) the Si3N4 mask is stripped; (4) a thin layer ofSiO2 is grown by thermal oxidation; (5) polysilicon is deposited by CVD and doped n+ using ionimplantation; (6) the polysilicon is selectively etched using photolithography to define the gate electrode; (7) source and drain regions are formed by doping n+ in the substrate; and (8) P-glass is deposited onto the surface for protection.
This 8-inch "wafer" of silicon contains 212 MediaGX™ processors produced on the 0.35 micron production line. (For comparison, a human hair is 50 to 70 microns wide.) (Photo courtesy of National Semiconductor)
Photo micrography captures intricate circuit lines hundreds of times smaller than a human hair.(Photo courtesy of National Semiconductor)
Another micrograph photo.(Photo courtesy of National Semiconductor)
A manufacturing associate wears a "bunnysuit" while handling wafers at this 1200-degree Centigrade furnace.(Photo courtesy of National Semiconductor)
At National Semiconductor's wafer fabrication plant in Arlington, Texas, many manufacturing processes are computerized.(Photo courtesy of National Semiconductor)
A common clean room requirement of 100 implies that no more than 100 particles of size 0.5 mm or greater can exist in 1 ft3.
National's wafer fabrication facility in South Portland, Maine, houses the latest sub-micron manufacturing equipment. Containers in foreground, called pods, protect wafers from dust particles.(Photo courtesy of National Semiconductor)
National Semiconductor's new micro SMD packaging enable dramatically smaller printed-circuit boards. Because micro SMD packages are smaller than chip capacitors, they look like mere dots on the smaller board.(Photo courtesy of National Semiconductor)
Until the release of the micro SMD package, a semiconductor device's die has always been much smaller than its package. With micro SMD, packaging can get no smaller because "The die IS the package!“(Photo courtesy of National Semiconductor)
Last year, National Semiconductor introduced the world’s smallest dual op amp, the LMC6035. Now a portfolio of products are available in this package -- a package so small that several devices fit on the head of a pushpin with room to spare.(Photo courtesy of National Semiconductor)
National Semiconductor's new four-, five-, and eight-bump micro SMD packages comply with a JEDEC standard. The chip-scale packages' solder-bump pitch is 5 mm. (Photo courtesy of National Semiconductor)
The IC manufacturing process consists of many steps. The probability of good yield can be computed from
Y = Yc Ys Yw Ym Yt
where Yi is the yield at each step.
Typical yield values are
Crystal (Yc ) – 50%
Wafer slicing (Ys ) – 50%
Wafer yield/processing (Yw ) – 70%
Wafer multi-probe testing (Ym ) – 10% - 90%
Wafer full testing (Yt ) – 90%
Y = (0.5)(0.5)(0.7)(0.5)(0.9) = 0.08 (< 10%)
The printed circuit board (PCB) is a laminated medium for mounting and interfacing electronic components, thus providing for their electrical connection.
The layers are made of copper foil conducting layers interspersed with insulating layers made of polymer composites reinforced with glass or paper fabrics. Copper foil thickness is around 0.0015 in, while the insulation layer ranges from 0.031 in. to 0.125 in. Single and double-sided boards are produced in quantity and then laminated to make multi-layer boards in a fairly complex process, since via holes are needed to electrically connect the different layers.
1. Board preparation– shearing to create the proper board profile, hole making to create tooling holes, and shaping operations to create tabs, slots and other features. These phases are followed with bar-coding and board cleaning.
2. Hole drilling– Circuit holes are drilled or punched to create insertion holes or via holes. Since the drill bit is usually small (< 0.05”) and required to pass through different layers having different properties, the drill speed is usually very high (100,000 rpm) and thus requires special drill motors/spindles.
3. Circuit pattern imaging and etching– uses either of two methods – screen printing (tracks > 0.01 in.) or photolithography (tracks < 0.01 in.) – to create the tracks and land of the circuit. The photolithography method is similar to that used in IC production. The only difference is that the photoresist covers portions of the copper layer and chemical etching is used to remove the exposed copper.
4. Plating– used to plate the holes to provide a conductive path. Uses either electroplating or electroless plating methods.
5. Cleaning/inspection- finished boards are usually cleaned, inspected and tested to complete the process. Visual inspection is used to find obvious flaws, while continuity testing is used to find more subtle problems, particularly in multi-layer boards. Finally, the board tracks and land surfaces are coated with solder to protect the copper.
Modern assembly plants use automatic insertion machines, and sometimes robots for non-standard parts.
The Fuji CP-643E combines high-speed placing with an innovative new PCB loading system to increase throughput. The machine achieves a placing speed of 0.09 sec/shot and can be loaded with up to 140 part types.
Electronics assembly: control technologies
Vision is used for testing/inspection, feature finding, and rigid-body correction.
Mechanisms and their end-effectors (vacuum grippers, finger grippers, etc.) must move to parts that will be deposited on the IC boards, then pick them up, move to the circuit board pad location, then deposit the part. The accuracy requirements can be in the thousandths of inches or less. The accuracy will depend on the lead pitch requirements(moving to 0.15 mm).
Vision is used for testing/inspection, feature finding, and rigid-body correction.
Because of errors in part presentation and the part picking, it is required that vision systems view these parts relative to the tool before placement to correct for part picking rigid-body errors (offsets) in both position and orientation. Similar errors exist for the placement of the circuit board on the board holder.
Control process 1
Control process 2
Process 1 (Tool process) Process 2 (Vision process)
Pick up part while(1):
Move part under camera Wait until signal5 == Part_there
Set signal5 to Part_there Take picture and load offsets
Wait until signal93 == Vsn_Done Set signal93 = Vsn_Done
Read offsets and adjust target Set signal5 = Part_not_there
Electronics board testing(after cleaning)
We will now see videos on circuit board assembly. Be sure to take notes because you will be tested on the video material!
Reference - “Electronic Manufacturing and Packaging in Japan,” Michael J. Kelly, Chair William R. Boulton, Editor, John A. Kukowski, Eugene S. Meieran, Michael Pecht, John W. Peeples, Rao R. Tummala, JTEC (Japanese Technology Evaluation Center) Panel Report, February, 1995
Note: See report link on class website
“The Japanese can do it; Americans can do it. The issue that separates the United States from Japan in high-volume, low-cost electronic assembly is neither technology nor manufacturing; it is primarily the will to take the measures necessary to compete and succeed.”
What have we learned?