digital design obsolescence

O'Boyle MAPLD 2005/P10231

Digital Design Obsolescence

John O’BoyleFor MAPLD September 2005

Military, Aerospace, and High Reliability IC Manufacturer


Defense Programs Still Need OLD ICs

• 30 Year Old ICs Are Still in Use in many modern High Reliability, Military, and Aerospace applications.

• Combining New Technologies and older devices leave Mil/Aero OEMs challenged with IC sourcing due to obsolescence.

• The Fabrication of Obsolete ICs Is Not Attractive due to low returns and matching original designs.


Issue : Diminishing Supply• In Some Cases the Parts

Just Vanish:– Take, for example, the Dual

RS-422 Line Drivers to the right

– National Semi unilaterally discontinued the supply of these devices on April 21, 2005.

– Why? Because they simply ran out, no close monitoring of the supply

– This means even the best managed programs may be vulnerable.


TODAY’s Key Challenge

How Does a Mil/Aero OEM Obtain Reliable, Accurate Reproduction of

Older Parts?

or

How Do They Entice the IC Foundry to Build Such Replacement Parts?

Elizabeth Basilio

Pose the today's challenge immediately to bring thought and interest for the audience to read further

Elizabeth Basilio

see notes page


Factors for Consideration• Buy Entire Remaining Inventory; But that’s

very expensive and many various Gov’t regs limit requisition quantities. – And, as a corollary to the RS-422 example, that is still

no guarantee; demand can outstrip supply.

• Use Commercial Parts From the Beginning; But they, too, are diminishing and are not suitable in all applications.

• So, do we look to the foundry for a solution?

Let’s See …


1. Foundry : Low VolumesA Fundamental Disconnect

• An Illustration – Teledesic (the early days)– Almost 1000 satellites (Close enough for this

illustration)– Assume 100 “Identical” parts per satellite, balance

are other hi-rel.– Build them all in one year (Not realistic, but suitable

for this example).– Spares at 100% of original build.– Complex die, Estimate die size 5 by 6 mm.– Technology: 0.25 Micron on 8-inch wafers.– Total fab, assembly, test yield = 85%.


• 1000 x 100 = 100k devices• Plus 100% spares = 200k• Total die needed: 200k/85% =

236k round to 250k die• Gross die per wafer 1000• Total 250k/1000 = 250 wafers• In 1996 top 10 IDMs

(Integrated Device Mfr.) were 20 million wafers per year

• 250/20 million = 0.00125 % • Bottom line: Volume is

insignificant for the foundries

Low Volumes = Low Profitability for IC Mfg This is Reality


2. Lack of Process Knowledge• Modern designers use tools with IP

embedded – they place blocks with 100s of transistors, or more.– Plus, design rules prohibit changes.

• Important when designing a complex digital device or the time to complete would be prohibitive doing “Stick” designs.

• Designers today enjoy no real process knowledge– No understanding of the nuances of the process used

to make their design at the foundry.


“Lack” – is a Real GapAn Example:

• Temp compensated bias driver – As temp changed, reference voltages A, B, and C remain unchanged.

• Why? – The process had very linear negative TC for VBE which was used in a ratio between D3 and Q6 to afford ideal positive compensation.

• A new designer tried to “Copy” the part but did not understand the process so the part failed to work.


3. Foundry : Economic Imperatives• Wafer Throughput and Yield

– Large scale manufacturing economics drive the foundries and fabs.

– The fixed costs are very high and short term variable costs are significant, too.

– The factories must produce many wafers just to reach breakeven.

• Cardinal Rules:1. “Fill the Fab”2. Minimize process variations: wafers out/wafers

started 100% (or As Close As Possible “Cut the Scrap”)


Incredibly High Investments• Over 68 foundries listed by FSA (Fabless

Semiconductor Association) today, not counting firms like Toshiba (not listed).

• Today a 130/90 nm Fab Costs $3 to $4 Billion. Plus expendables.

• Opportunity cost related to stopping a running fab to insert 250 wafers for an annual buy is expensive.– This is applies to most fabs, 12-inch, 8-inch and even 6-inch.


Breakeven Is High

Figure 18 Inch Revenue to Breakeven

$-

$5.0

$10.0

$15.0

$20.0

$25.0

$30.0

$35.0

5000 10000 15000 20000 25000 30000

WSM

Rev

enu

e ($

M)

8" Rev @ $1000 8" Rev @ $800 8" Rev @ $600 Breakeven

• Figure 1 (8 inch 0.18 micron fab):– At different wafer prices the monthly breakeven moves from $15

Million and 15k wafers for $1k Per wafer to $16 Million for 20k wafers at $800 each.


Breakeven is Very High

Figure 212 Inch Revenue to Breakeven

$-

$10.0

$20.0

$30.0

$40.0

$50.0

$60.0

$70.0

$80.0

5000 10000 15000 20000 25000 30000

WSM

Rev

enu

e ($

M)

12" Rev @ $2500 12" Rev @ $2000 12" Rev @ $1500 Breakeven

• Figure 2 (12 inch 90 nm fab):– At $2500 per wafer the monthly breakeven Is $40 Million for 17k wafers

and at $1500 breakeven will not be achieved until the variable costs come down.

Yikes!


4. Foundry : Scarce Expertise• Today’s Obsolete Device Designer relies on

modern tools and experience and knowledge about process – a True Artisan.

• Gone Are the Days of Pencil & paper and Karnaugh maps (Min-sums); Mylar Grids with Mylar transistors and hand-drawn resistors; “Digitizers” and Rubyliths; 500x cameras that floated on Hg; chrome masters and glass plate masks.


Tackling Obsolescence Today– A Few Solutions

• Size Does Matter – Hi-Rel volumes too small to be attractive. So think SMALL

• Emulate – Works when no other solutions are available.

• Create – NEW APPROACH; Much closer to original and more reasonable in investment.


1. Solution – Size Does Matter• The Large Foundries (TSMC, UMC, SMIC,

etc.) are out of reach to small Hi-Rel OEMs.

• Small “Research Oriented” Foundries (Typically under 10,000 wafers a year, sometimes much lower) will still run special lots.– Caution: Their processes are not as well controlled as

modern flows, but they are better than anything else available.


2. Solution – Emulate …• There are a couple of approaches available which

allow a design team to emulate an obsolete part, right down to the timing delays.

• Works well for logic, the analog function is still in question, but they’re working on that too.

• There are available programmable approaches.

• May be a possible low volume obsolete parts replacement.


3. NEW APPROACH: The Multi-Project Die (“MPD”)• Amortize Mask Tool Costs Across Several

Parts– Derive several different options from “MPW” Die– Metal mask programmable – Allows wafer hold at metal

and patterning to meet orders – Quick Turns

• Higher WSM (Wafer Starts per Month) figures to foundry partner

• Not constrained by Max GDPW (Gross Die Per Wafer)

• Flexible Family Sets; Memories, sequential and combinatorial logic – 34 different parts on first MPD.


Options for MPD• I/Os:

– TTL Totem Pole– DTL– Multiple I/Os

• PROM – Metal Mask– Core covers major and

Minor densities in range (S, M, L)

– Fusible links next

• Foundry holds average of 24 wafers at metal. When down to 12, they start another 24.

Four Peripheral Drivers, One Wafer:QP1631, QP1632, QP1633 and QP1634


Metal Options (OP 1)

Note, One ConnectionScheme in OP 1


Metal Options (OP 2)

And Another

Scheme in OP 2


Summary• Economies of scale are opposite between a

foundry and an obsolete device maker.– Partnering with the right manufacturing partner is key

• An obsolete device designer needs process knowledge to tailor the design to take advantage of “anomalies”.

• The obsolete designer must find creative ways to fabricate parts:– Focus on what is important to achieve performance– Target smaller foundries– Adapt designs/layout(s) for flexibility in die size while

keeping costs within reason.

digital design obsolescence

Documents

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mapld 2005p1023low volumes

replacement parts

identical parts

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