The life of a chip
How one chip goes from a design to someone's hands
Between a finished design and a product in someone's hands, a chip passes through roughly four places. The design company hands its design to a wafer fab, where it becomes a set of photomasks. The fab builds the circuits on wafers layer by layer: this is what the industry calls the front end. A test-and-assembly house tests every chip, cuts the wafer apart, packages the chips and tests them again: the back end. Finally the customer's factory builds them into a product. This page walks through each step in order. Each step also matches part of the main story of fab24hr, The life of a chip: a prologue and 12 chapters that follow a fictional hearing-aid chip, "Glowmere", all the way, and every section below has a link that starts that chapter.
The whole path in one table
| Step | Where | Main story |
|---|---|---|
| Tape-out and photomasks | Design company, mask shop | Prologue |
| Pilot run on the R&D line | The fab's R&D line (front end) | Chapters 1–4 |
| Mass production | The production fab (front end) | Chapters 5–8 |
| Wafer test (wafer sort) | Test-and-assembly house, or a dedicated test house (back end) | Chapter 9 |
| Packaging | Test-and-assembly house (back end) | Chapter 10 |
| Final test and reliability | Test-and-assembly house (back end) | Chapter 11 |
| Shipping and dry packing | The test-and-assembly house's shipping area | Chapter 11 |
| Into a product, into someone's hands | The customer's assembly plant, the user | Chapter 12 (finale) |
Tape-out and photomasks
When a chip's design is finished and checked (does it break any of the fab's design rules, and does the layout match the circuit diagram?), the design company hands the final design to the wafer fab. That handoff is called tape-out. The design is then made into a set of photomasks: one glass plate for each layer of the pattern, like the negatives for a photo, and a set often has a few dozen. Changing the design after tape-out means making new masks, which is expensive and adds months, so the checks before tape-out are thorough.
In the game
The prologue of the main story, a few short paragraphs before chapter 1 with nothing to play: a small hearing-aid company has designed its own chip for the first time, "Glowmere", meant to make a button battery last several days longer (the company's founder, Ms. Shen, has a father who wears hearing aids). Its design goes to the fab and becomes a set of masks.
Pilot run on the R&D line
A new process or a new product is often made first on the fab's R&D line. This first batch is the pilot run, and the point is to find the problems and measure the yield. One lot is split into groups that each change a single condition (a split lot), and a few wafers are made a little fast or a little slow on purpose (corners), to see whether the design can handle the variation every fab has; when the wafers are done, the test keys in the scribe lines are measured (WAT), and every chip is tested and drawn on a wafer map. Reliability has to be proven too: a common HTOL test runs three lots of 77 chips each, powered at high temperature for 1,000 hours, with not a single failure allowed. Once it is stable and passes the transfer review, the conditions are written into the process of record (POR) and handed to the production fab.
In the game
Act one, the R&D line (chapters 1–4): you are the R&D integration engineer. You decide how to split the first 12 wafers, read the cause from the shape of the failures on a wafer map, and on the night before the transfer review decide whether to recommend a risk start. In chapter 4 you are the R&D process engineer, writing an alarm limit into the last box of the process of record handed to the production fab. People further down the line live with all four of these decisions.
Mass production
Once it is handed over, the production fab makes the chip in volume by the process of record. This is the front end: deposit a thin film, print the pattern onto it with litho, etch it, clean, then on to the next layer, building the chip up layer by layer. From wafer start to finish, a lot of wafers often takes weeks to months; the tools run around the clock, so when something goes wrong, someone gets a phone call in the middle of the night. When the wafers are finished they are measured once more (WAT), boxed and shipped to the test-and-assembly house.
In the game
Act two, the production fab (chapters 5–8): about half a year after the pilot run, one lot of Glowmere, the hot lot H-2417, is stuck inside the etch tool ETCH-03. You are the process engineer: the 02:47 phone call, firefighting in the morning, a manual rework in the afternoon, a yellow light in the evening. The limit written into the process of record in chapter 4 comes back on this day. On the same day, Manufacturing, the equipment engineer and the litho engineer each see a different problem; play them in A day in the fab by switching roles.
Wafer test (wafer sort)
The wafers go to a test-and-assembly house (or a dedicated test house), and before they are cut apart, every chip is tested: fine needles on a probe card touch each chip's pads while a tester runs the test program, one measurement after another. This is called wafer test, wafer sort or CP. Each chip lands in a bin, one for good chips and one for each way of failing, and the results are drawn by position as a wafer map; only the good chips go on to packaging. Where to set the limits is a trade-off: too tight and good chips are thrown out; too loose and bad ones reach the customer.
In the game
Act three, the test-and-assembly house, chapter 9, "Standby Current": you are the test engineer, and Glowmere's first production wafers have arrived. Find the most common failure on the bin Pareto chart, see where it sits on the wafer, then decide where to draw the standby-current limit on a chart of how the readings are spread. Whether the R&D line ran the fast corner (FF) decides whether you have any numbers to compare against.
Packaging
Packaging puts the chip in a case that protects it and connects it to a circuit board. The wafer is ground thinner from the back and diced into single chips. In the game, Glowmere goes into a small SiP module: solder paste is printed on a tiny board, and a few small resistors and capacitors are placed on it and soldered in an oven (SMT); the chip is glued down (die attach), its pads are connected to the board with metal wires finer than a hair (wire bonding), and the whole thing is sealed in plastic (molding) and cut into single modules. To check that the wires are attached firmly, a few are pulled until they break (pull test), noting the force and where they broke; once sealed, the wires can't be seen from outside, so the modules are checked with X-rays.
In the game
Chapter 10, "The Ball Lifted": you are the assembly process engineer. You walk the assembly line with the line leader, then two wires in the wire bonder's pull test come out wrong: the ball on one end lifted clean off the pad. Do you stop the tool, change the capillary and retune it, and re-sample every tray bonded that day, or keep it running and pull-test every two hours?
Final test and reliability
The sealed modules are tested again (final test): a wire may not be connected, and some characteristics change once a chip is packaged; a handler feeds the parts into a test socket one at a time and sorts the good from the bad. Reliability asks a different question, whether it will still work after a while: plotted over time, the failure rate of electronic parts looks like a bathtub, high right after they are made (early-life failures), low for a long stretch, then rising again with wear. Before shipping, a sample can be run powered at high temperature for two days to a week, to see how many fail and estimate whether the lot has too many early-life failures; but a sample can only estimate, it can't catch every weak part. Running every part through a first stretch (burn-in) takes a day or two plus special fixtures, and most consumer products don't do it for every part. The HTOL test is done once before a new product launches, and in mass production it becomes periodic sampling, not a gate every lot has to wait for.
In the game
Chapter 11, "The Night Before Shipping": you are the test-and-assembly house's customer liaison. Quality goes through the pre-shipment checklist with you item by item, and the decisions from earlier chapters show up here as green or yellow. The customer asks whether it can ship tomorrow; you decide whether to run an early-life sample for two days first, or ship on time.
Shipping and dry packing
Tested parts go one by one into the pockets of a long plastic tape that is wound onto a reel (tape & reel), so the customer's machines can pick them up automatically. Plastic packages absorb moisture from the air, and when a part is soldered to a board, the water inside turns to steam all at once and can crack the package; so parts that are sensitive to moisture are baked dry and sealed in a moisture barrier bag with desiccant and a humidity indicator card that changes color when damp (dry pack). The bag gets a moisture caution label and a label with the part number, quantity, lot number and date code, so that if something goes wrong, it can be traced back to the wafer lot and the assembly run.
In the game
The last stop of chapter 11 is the shipping area: reels, desiccant, humidity cards, moisture barrier bags. You sign the shipping form, or mark the shipment as paused.
Into a product, into someone's hands
The reels go to the customer's assembly plant, where machines place the parts on circuit boards, solder them in an oven and build the boards into products. In the game the product is a hearing aid: a microphone picks up sound, it is amplified, and a tiny speaker sends it into the ear; it runs on a zinc-air battery that starts working when its sticker is peeled off and lasts from a few days to about two weeks. The less current the chip leaks while idle, the longer the battery lasts; if a chip has a hidden defect, it usually shows up in the first weeks to months of use, and then the product comes back as a return and the failed part is taken apart to find the cause (failure analysis).
In the game
The finale, chapter 12, "Into His Hands": you are Mr. Shen, a retired primary school teacher in his fifth year of wearing hearing aids. His daughter brings home the first hearing aid her company has made. You put in the battery and put it on; at half past ten, when the old one would long since have died, you sit in the living room and hear your wife talking in the kitchen. Every decision in the earlier chapters leads to one of three endings: "On the shelf on time", "A little late, nothing came back" or "Three months later, a batch came back".
How the main story works
After you clock in, fab24hr has two ways to play: The life of a chip is the main story; A day in the fab lets you pick a role and play the shift that matches your device's clock. The main story has a prologue and 12 chapters in four acts:
| Act | Chapters | You are |
|---|---|---|
| Act one: the R&D line | 1–4 | R&D integration engineer, R&D process engineer |
| Act two: the production fab | 5–8 | Process engineer (four shifts of one day) |
| Act three: a test-and-assembly house | 9–11 | Test engineer, assembly process engineer, customer liaison |
| Finale: into someone's hands | 12 | Mr. Shen |
Each chapter is still one person's day, and the chip is what gets handed along: earlier decisions reach the people who come later and decide which of three endings you get. A chapter takes about ten minutes; you can play in several sittings, and progress is saved in your browser. The wafer counts, times, limits and days mentioned under "In the game" are game settings, for illustration only.
Common questions
How long is the main story, The life of a chip?
A prologue and 12 chapters of about ten minutes each: one to two hours in all. You can play it in several sittings: progress is saved in your browser, and when you come back, the home screen offers to continue from the next chapter.
Can I start from any chapter?
Yes. The link under each section of this page takes you straight to that chapter, and in the game, the "The life of a chip" tab of the codex has a chapter list (once you have played, the Chapters button on the home screen opens it too): tap a chapter to start it. Chapters you haven't played are filled in the way they usually go, so you don't have to start from the beginning; play them in order and earlier decisions carry forward.
Do I need to sign in to play?
No. Open it and play; progress is saved in this browser.
Is it real?
The companies, the product, the people, the lot numbers and the figures are fictional game settings and do not represent any company; Glowmere is a made-up chip. What each step involves, and why it is done that way, is drawn from public, general sources: textbooks, industry standards, university courses and papers.
What are the front end and the back end in semiconductors?
In the industry, the front end usually means the wafer fab building the circuits on wafers layer by layer, and the back end means assembly and test: testing the chips on the wafer, cutting them apart, packaging them and testing them again. Inside a fab, engineers also use front end and back end for the first half of the process (building the transistors) and the second half (the metal wires that connect them), which is a different meaning; context tells you which.
What is assembly and test?
Packaging and testing. Finished wafers go to a test-and-assembly house: first every chip is tested on the wafer, then the wafer is cut apart and the chips are put into small packages, and once sealed they are tested again before shipping to the customer. Four sections of this page (wafer test, packaging, final test and reliability, shipping and dry packing) are what a test-and-assembly house does.
- What is fab24hr?: the two ways to play, the four shifts, common questions, sources
- A day in the life of a fab engineer: who does what (PE, EE, PIE, manufacturing), and the day hour by hour
- Who works in a chip fab: technicians, manufacturing, process, equipment, litho, facilities, integration, R&D, the chief, the vendor, and test and packaging at the test-and-assembly house: each role's day
- Chip fab jargon in plain English: MO, Hold, Q-time, OCAP and the rest, one plain sentence each
- fab24hr in the classroom: 20- and 40-minute lesson plans, one chapter of the main story per lesson, discussion questions, devices and privacy
- About and press kit: trailer, gameplay clips, descriptions and key facts