Wafer Map — User Guide¶

This guide describes the display and analysis features of the wafer map viewer. It is written for users who may be semiconductor test engineers, device engineers, and yield engineers or anyone else who may use a wafer map application — not for developers integrating the wafermap library.

Some features depend on what data the application has loaded (bin names, test definitions, spec limits, reticle geometry). Where this applies it is noted.

Getting oriented. The wafer map is an interactive viewer. A toolbar is always present at the top-right of the map — use it to change what the colours represent, toggle overlays, rotate or flip the wafer, zoom, select dies, and open the summary panel. Hover any die for a tooltip; the panels and tooltips always report the original die grid coordinates, never the on-screen position after a rotate or flip.

1. Reading the map¶

1.1 Die grid and coordinates¶

Each square on the wafer represents one die. The position labels you see — in tooltips, axis ticks, and selection readouts — are die grid coordinates: usually the X and Y step indices from the prober (integers such as −7, 0, 5). They are not millimetre values.

These coordinates are always the original grid values. Rotating or flipping the display does not change the coordinate labels — a die at (3, −2) always reads (3, −2) regardless of how the wafer is oriented on screen.

1.2 Wafer orientation¶

The notch (shown as a V-notch or flat edge) marks the physical reference edge of the wafer as configured. Use the Orientation toolbar controls to rotate or flip the display to match your convention; die coordinates are unaffected.

An example wafer bin map above and below the same wafer rotated 90°. The notch has moved, but die coordinates — shown in tooltips — remain their original grid/prober values.

1.3 Die appearance¶

No-data grey and partial-die grey are visually distinct. A no-data die is not a fail; it simply has no result recorded. Edge-excluded dies are shown dimmed and are not counted in yield calculations.

1.4 Legend and colorbar¶

Bin modes show a discrete colour legend: one swatch per bin, with bin number and name if the application has supplied bin names. Passing bins are listed first, then failing bins from the most dies to the fewest — the same order as the Summary panel and reports.

Value mode shows a continuous colorbar: the colour scale runs from the minimum to maximum value, with units when available. The colorbar is informational only — clicking it has no effect. To switch to a pass/fail view, use the Spec pass/fail or Test pass/fail option in the Overlays menu (available when spec limits are defined, or a recorded verdict exists, for the active test).

Spec pass/fail mode replaces the colorbar with a small spec legend: Pass, Fail high, and Fail low swatches (only the categories that apply to the test's limits) with a die count beside each. This judges dies against the test's spec limits (limitLow / limitHigh).

Test pass/fail mode replaces the colorbar with a Pass / Fail legend and die counts, coloured by the tester's own recorded verdict for that test — not a spec-limit judgement. A test with no measured value (a functional, go/no-go test) always displays this way; selecting it switches the map into Test pass/fail automatically, since there is nothing to plot on a gradient.

Every map also shows a short title by the colorbar or legend naming what is displayed — the test name (and number, in spec mode), the bin type, or the stacked wafer count.

Clicking a bin swatch in the legend filters the display to that bin (see Highlight bin).

1.5 Wafers and dies with no position data¶

Not every die necessarily has a reported grid position — some data sources supply bin or test results with no X/Y coordinates at all, for some or every die on a wafer.

A fully positionless wafer never renders as a map or gallery card — showing dies at fabricated positions would risk being misread as real spatial layout. Instead the card shows a compact summary matching the active plot mode: a bin breakdown (coloured the same as a positioned card's own bin legend) for hard/soft-bin modes, or a histogram for value mode — coloured through the same colour scheme, log-scale, and spec/data-range settings the map itself uses, so switching those in the toolbar updates the chart the same way it would a real map. A View die list toggle switches to the full per-die table (position/site, hard bin, soft bin, every test value) with its own CSV export; View chart switches back.

A mixed wafer — some dies positioned, some not — renders its normal map for the positioned dies, plus an expandable "+N dies without position data" footer beneath the card. Expanding it (click the footer or its chevron) shows the same chart/die-list toggle, scoped to just the unpositioned subset.

The toolbar's spatial-only controls (zoom, pan, box select, save image, orientation, overlays, legend position) are hidden on a fully positionless card, since there's no map for them to act on. Plot mode and colour scheme stay available — both still drive what the summary shows.

Findings that depend on physical layout — edge ring, quadrants, sectors, reticle position, cluster and pattern detection — only ever consider positioned dies, so a positionless wafer contributes none of these. Everything else — yield, bin counts, per-test statistics, and the Insights tab's histograms/correlation/scatter — still includes every die, positioned or not.

2. Plot modes¶

The active plot mode determines what the colour of each die represents. Use the Plot mode toolbar dropdown to switch. Available modes depend on what data the application has loaded.

Stacked modes are only available on lot-stack maps (multiple wafers combined into one display). The panel identifies how many wafers were stacked and which aggregation method is active.

Test Value mode — colorbar range and spec limits¶

When spec limits are defined for the active test, two additional display options become available:

• Colorbar range — Data / Spec: switches the colorbar scale between the actual data extent and the spec limit bounds. This affects only the colorbar's range, never how out-of-spec dies are shown. In both ranges every die is coloured by the gradient so you can read the value distribution, and out-of-spec dies are marked with a triangle — pointing down (▽) for below LSL, up (△) for above USL — so they stand out without leaving the distribution. The triangle is drawn black or white per die for contrast against its own colour, so it stays visible under any colour scheme, and its shape (not colour) carries the below/above-limit meaning.
• Spec pass/fail: when active, dies within spec are shown in a pass colour and dies outside spec are highlighted — blue for below the Lower Spec Limit (LSL), red for above the Upper Spec Limit (USL). Both flags apply independently; a die can be flagged on either or both limits. A spec legend replaces the colorbar, listing each applicable category with its die count.

Some tests have no measured value at all — a continuity check or any other go/no-go test, where the only result is a recorded pass or fail. Selecting one of these functional tests as the active test switches the map into Test pass/fail automatically: a Pass/Fail legend by die count, coloured by the tester's own recorded verdict rather than a spec-limit judgement (there is no gradient to fall back to). Test pass/fail is also available as an Overlays option on an ordinary parametric test when it carries recorded verdicts, as an alternative to spec-limit judgement.

3. Toolbar controls¶

The toolbar sits at the top-right of the map and is always visible. Controls that are not applicable to the current mode are hidden automatically. (Hovering the map shows die tooltips — a separate thing from the toolbar, which is always present.)

Single map¶

	Control	Description
	Plot mode	Switches the active plot mode (see Section 2). When multiple tests are available, a test selector appears alongside it.
	Overlays	Check-menu of optional display layers: XY axis indicator, ring boundaries, quadrant lines, die coordinate labels, reticle grid (when geometry is configured), Spec pass/fail (Test Value mode with limits), Test pass/fail (Test Value mode, active test is functional or has recorded verdicts), and Mark failing dies (bin modes only). Clear overlays at the foot turns off everything in the menu at once, and is greyed when nothing is on — so the menu also answers "is anything active?" without you auditing every row.
	Colour scheme	Picks the colours for the map on screen. In Hard Bin and Soft Bin modes it lists bin colours (Default, Colour-blind safe); in every other mode — including the stacked modes, which show values — it lists value colours. The two are separate choices, so changing one never resets the other. Value gradients run dark at the low end and bright at the high end, so on a stacked map the healthy wafer sits back and a defect ring or scratch stands out; Reverse gradient flips that when the low end is the one you care about. When bin definitions carry their own colours, Use colours from bin definitions turns them on or off. (Mark failing dies is in Overlays, beside the pass/fail display it belongs with.)
	Log scale	Test Value and Stacked Test Values modes only. Applies a log₁₀ scale to the colour mapping. Only active when all displayed values are positive. Hidden whenever a pass/fail display is active or the active test is functional.
	Colorbar range	Test Value mode with spec limits only. Toggles the colorbar between the spec-limit range (default — the colours mean the same thing on every wafer, so maps are comparable) and the data range (stretches the scale to the values actually present, which shows more contrast but is not comparable between wafers).
	Legend style	Bin modes only. Controls where the bin legend is positioned relative to the map: Default (right), Compact, Left, Top, Bottom, or Floating.
	Orientation	Menu of display transforms: Rotate 90° clockwise (applies cumulatively), Flip horizontal, Flip vertical, and Reset orientation. These change only how the wafer is drawn — die coordinates in tooltips and labels are always the original values, whatever the orientation. Reset is worth knowing about: rotation and mirroring do not combine in the order you applied them, so undoing a few clicks by clicking again does not reliably get you back — Reset does, and is greyed when you are already there.
	Zoom mode	Click and drag to draw a zoom region.
	Zoom in	Zooms in one step.
	Zoom out	Zooms out one step.
	Reset zoom	Returns the map to the default fitted view.
	Pan mode	Click and drag to pan the map.
	Box select	Click and drag to select a rectangular group of dies (see Section 4.3).
	Insights	Swaps the map for this wafer's own chart suite — yield, bin breakdown, process capability, and more (see Section 8). Only shown when the application has enabled it.
	Expand	Opens the map in an enlarged modal overlay. A maximise button in the modal grows it to fill the window (or press F). Press Esc or click outside to close. Useful for detailed inspection without changing the main view. Works in the Insights view too, where it opens the whole chart suite in a wide modal — useful because those charts interact and are best read side by side. Individual charts also have their own expand button.
	Save image	Downloads the current map view as a PNG. Captures the canvas as displayed, including all active overlays and the legend.
	Findings	Opens or closes the Summary panel (see Section 6).
	Data warnings	Appears only when there is something to report about the data behind the map. Click it for the details. A red ⛔ means the map may be positionally wrong — usually that wafer geometry was guessed rather than supplied, so dies may not sit where they appear to. An amber ⚠ means something expected is missing or was skipped, but what is drawn is correct.
	User guide	Opens this guide.

This guide's own window (and a gallery card detached into its own window, see Section 3 — Gallery below) is a floating window, not a modal — its header shows minimize, maximize, and close buttons, and it can be dragged and resized by its corner grip. Minimizing collapses it to a small title strip without closing it; click it again to restore.

Highlight bin — in bin modes, click any bin swatch in the legend to highlight that bin and dim all others. Click again to clear. Useful for isolating a specific failure category across the wafer.

Bin 2 (Fail) highlighted — all other bins are dimmed.

Bin colours — a bin's colour tells you whether it passed before you read the legend: passing bins are always shades of green and failing bins never are, whichever bin numbers your test program uses. Each bin number keeps its colour: bin 7 is the same colour in every lot, every gallery and every screenshot, however many dies it holds, so you can learn your program's colours. Hard and soft bins are coloured separately, so hard bin 3 and soft bin 3 are different colours. A colour scheme has a limited number of colours, so bins far enough apart in number repeat one — when two of them are on screen together a Data warnings entry names them, and you can tell them apart with the legend, the tooltip, or by highlighting one bin at a time.

Overlays¶

Use the Overlays menu to toggle optional display layers on and off:

• XY axis indicator — shows X and Y axis lines through the wafer centre
• Ring boundaries — concentric ring divisions that match the spatial analysis zones
• Quadrant lines — divides the wafer into N, S, E, W quadrants
• Die coordinate labels — draws the (x, y) grid position inside each die (useful at high zoom)
• Reticle grid — stepper field grid (only shown when reticle geometry is configured)
• Spec pass/fail — pass/fail colouring for Test Value mode, judged against spec limits, when the active test defines them
• Test pass/fail — pass/fail colouring for Test Value mode, coloured by the tester's recorded verdict; always on for a functional (no measured value) active test

Ring boundaries, quadrant lines, and XY indicator all active.

Keyboard shortcuts¶

Gallery¶

The gallery control bar applies to all cards simultaneously.

	Control	Description
	Plot mode	Switches the plot mode for all cards.
	Overlays	Toggles display layers for all cards simultaneously.
	Colour scheme	Picks bin colours (bin modes) or value colours (other modes) for all cards, including Reverse gradient.
	Orientation	Opens the rotate/flip controls, applied to all cards.
	Columns	Sets the number of columns in the card grid.
	Save image	Downloads the full gallery grid as a single PNG.
	Aggregation method	Stacked modes only. Selects how values from multiple wafers are combined per die position: Mean, Median, Std Dev, Min, Max, or Count.
	Log scale	Test Value and Stacked Test Values modes only. Applies a log₁₀ scale to the colour mapping for all cards.
	Legend style	Legend on each map adds a legend to every card as well as the shared one above the grid (off by default). While it is on, bin modes also let you choose where that legend sits on each card.
	Colorbar range	Test Value mode with spec limits only. Toggles all cards between the spec-limit range and the data range. Leave it on spec limits when comparing wafers — the data range rescales per view.
	Summary panel	Opens or closes the Summary panel covering every wafer in the gallery.
	Insights	Swaps the grid for a chart suite covering every wafer — yield, bin breakdown, process capability, and more (see Section 8). Only shown when the application has enabled it.
	Data warnings	Appears only when something is worth reporting about the wafers shown. Collected across every wafer and de-duplicated, so a problem affecting all of them is stated once rather than repeated per card.
	User guide	Opens this guide.

Click a card's expand button to detach it into its own separate window with the complete single-map toolbar (falls back to a floating window inside the page if separate windows aren't available in your environment). The vacated grid card becomes a placeholder whose own button reattaches it; closing the detached window does the same.

4. Interacting with dies¶

4.1 Hover¶

Hovering over a die shows a compact tooltip. It always includes the die grid coordinates (x, y), and a retest count if the die was probed more than once. The rest depends on the active plot mode:

• Bin modes — the die's bin verdict (number and name, if named), plus a note of how many test values are recorded for the die
• Test Value mode — the active test's value in bold, flagged when it is out of spec, with the remaining tests summarised as "+N more tests"
• Stacked modes — the single aggregated value or count at that position

4.2 Zoom and pan¶

Scroll to zoom in and out. Click and drag to pan when in Pan mode. The toolbar also provides dedicated Zoom mode (drag to draw a zoom region), Zoom in, Zoom out, and Reset zoom buttons. Tooltips and die selection remain accurate at all zoom levels.

4.3 Box select¶

Switch to Box select mode in the toolbar, then click and drag to draw a selection rectangle. The application may display statistics or details for the selected dies. This is useful for comparing a sub-region against the full wafer. Use Ctrl / Cmd + click to add individual dies to the current selection. Press Esc to clear.

A block of dies near the centre is shown pre-selected. Choose Box select in the toolbar and drag to make your own selection, or Ctrl/Cmd + click individual dies.

5. Findings panel¶

When spatial analysis has been run, the Findings panel lists statistically detected patterns on the wafer. Open it from the toolbar.

Each finding shows:

• Severity — Unusual, Notable, or Info (ordered most to least significant)
• Description — plain-language summary of what was detected and where
• Click to highlight — clicking a finding highlights the affected dies on the map with a black-and-white outline, visible against every colour scheme

Severity reflects how strong the statistical evidence is. Unusual findings have both a very low adjusted p-value and a large effect size — they are reliably important. Notable findings are statistically significant with a meaningful effect but not as extreme. Info findings pass the significance threshold at lower strength and are worth reviewing but may reflect smaller or noisier patterns.

Findings panel open showing a detected edge-ring pattern. Click any row to highlight the affected dies on the map.

A failure cluster finding: affected dies highlighted with a white-and-black outline.

Finding types¶

Which finding types are active depends on the application's analysis configuration.

When a spatial pattern classification is detected alongside supporting regional findings (ring, quadrant, sector), the panel groups them together — the pattern classification is the primary finding and the regional findings provide supporting detail.

6. Summary panel¶

The Summary panel docks next to the map and gives you the wafer or lot at a glance, with findings sitting directly under the headline numbers so a clicked finding can highlight the affected dies right there. Open it from the toolbar.

The Summary panel open alongside a single wafer. Click any finding to highlight the affected dies.

Sections, top to bottom:

• Summary — die and wafer counts, yield, and the population the rest of the panel is computed over. For several wafers the heading names them: Lot LOT123 · 13 wafers when every wafer comes from that one lot, otherwise 26 wafers from 2 lots (or just 13 wafers when the data records no lot). The panel only says "lot" when it really is one lot. "Mean wafer yield" is an unweighted mean of each wafer's own yield; it is deliberately not the same statistic as the bin breakdown's pass-bin share, which weights every die equally. The two agree only when die counts are even across the wafers.
• Findings — detected anomalies, most severe first. Severity chips narrow the list; Kind and Region dropdowns appear once there are enough findings to be worth narrowing.
• Bin breakdown — bars as a share of dies, pass bins first and then failing bins by descending count, so the dominant failure mode is at the top. It follows the map's plot mode: a soft-bin map gets a soft-bin breakdown. When a wafer carries both bin types, a Hard / Soft selector in the section header overrides that.
• Region yield — ring yield by default, with a Ring / Quadrant selector. Ring is the default because edge roll-off is the pattern that dominates real wafer maps; a genuinely asymmetric quadrant is reported as a finding above, with a significance test behind it.
• Wafer yield (several wafers only) — one bar per wafer with the median marked. Wafers are in slot order by default, since that is what makes a slot-correlated pattern visible; a Slot / Yield selector re-sorts. Wafers far below the rest are labelled "low outlier".
• Test values — per test: mean, Ppk, and spec yield. Ppk (not Cpk) because it measures against the overall spread, including wafer-to-wafer variation, which is what the dies actually ship against. The full descriptive statistics — min, quartiles, median, max, σ, both spec limits, and all four capability indices — are in the summary report and the CSV export.
• Functional tests — pass/fail counts and pass rate per functional test.

Every section header can be collapsed, and stays collapsed as the panel re-renders.

A Summary report button (when present) opens a printable full-detail report — yield, bin breakdown, ring and quadrant statistics, the full per-test table with Cp/Cpk/Pp/Ppk, and the findings list — and can be saved as a PDF from your browser's print dialog.

Why some findings name two bins¶

A finding may read "hard bin and soft bin 3 (Fail) (same dies)". That is one group of dies counted in two bin spaces, not two separate groups added together. (When the two bins carry different names, both are spelled out in full.) Hard and soft bins are independent numbering systems, so this wording appears only when the two happen to cover exactly the same dies — reporting it twice would look like two independent problems.

For the same reason, when a single pass bin is configured you will see the yield finding for a region but not a separate finding for the pass bin itself: "pass-bin occurrence is 22 points lower" and "yield is 22 points lower" are the same sentence.

Nothing is discarded — an application reading the findings programmatically still receives every one of them.

For lot-level views (gallery), the panel shows lot-level findings, and the Wafer Yield section badges each wafer with its own findings count — click a row to open that wafer. There is no separate wafers tab: every wafer appears in that one list, including the ones with no findings, which is what lets you see a low-yielding wafer that nothing flagged.

7. Lot-stack maps¶

A lot-stack map combines multiple individual wafer results into a single composite view. The display clearly identifies this: the number of wafers included and the aggregation method in use are shown in the panel header (for example, "3 wafers · mean") so you know you are not viewing a single wafer's data.

Individual die coordinates are preserved. For each die grid position, results from all wafers are aggregated into a single value or bin count according to the selected aggregation method.

Stacked plot modes¶

Switching to a stacked mode changes what each die's colour represents:

Aggregation method¶

In Stacked Test Values mode, use the Aggregation method toolbar button (Σ) to choose how values from each wafer are combined at each die position:

Gallery stacked modes¶

In a gallery, stacked modes are always available in the control bar. Switching to a stacked mode shows one card per bin category or per test parameter, aggregated across all wafers in the gallery.

Stacked Hard Bins mode: each die position is coloured by how many wafers had bin 1 (Pass) or bin 2 (Fail) at that location.

8. Insights tab¶

The Insights toolbar button (single map or gallery) swaps the wafer view for a chart suite computed from the same die data — without leaving the toolbar. Click it again to return to the map. Independent of the Findings sidebar (Section 6) — the two toggle independently, and opening one never hides the other's toolbar button, since Findings has nothing to highlight against once the map is replaced.

Insights is organized into three sub-tabs:

• Overview — a test pass rate chart showing which test fails most (and, with "Group by" active, whether it fails more in one split than another). It offers up to three ways of judging, whichever the data supports: Spec limits (the value against its limits), Tester flag (the pass/fail the tester itself recorded, which a parametric test carries whether or not limits were exported), and Functional for pass/fail-only tests. The two parametric views can disagree — guard bands and dynamic limits routinely cause it — so the card reports how many dies the two judged differently rather than picking one for you. Alongside it, headline tiles stating the population (wafers, dies analysed, and for a lot the mean wafer yield — an unweighted mean of each wafer's own yield, not the die-weighted figure), a yield bar labelled with the pass bins actually in use and marked with the median, a hard/soft bin pareto, and ring/quadrant regional yield plus the full per-test statistics table.
• Distributions — process capability (Cp/Cpk/Pp/Ppk for tests with both a lower and upper spec limit; tests missing a spec still appear, normalized onto their own range and sorted by variability), a test-value box plot, a value histogram, and a wafer-to-wafer trend — one point per wafer at its mean, ±1σ whiskers, the mean of all wafers dashed across (labelled the "lot mean" when they all come from one lot), and spec limits where the test has them. The trend is always in slot order, deliberately: drift across a cassette only reads in the physical sequence, so there is no sort control to destroy it. Clicking a capability box drives the box plot, histogram and trend onto that same test automatically.

The box plot, histogram and trend share one row of axis controls, kept in sync across all three so switching between them never re-reads the same data on a different scale: Axis includes limits widens the axis to cover LSL/USL even where the data sits well clear of them (on by default only when doing so still leaves the data at least a third of the axis — otherwise a generous spec window would squash a perfectly capable distribution into a sliver), and Clip outliers narrows the axis to a robust range (the Tukey fence, 1.5× IQR beyond Q1/Q3) so a handful of extreme values don't stretch the axis until the rest of the distribution reads as a flat line. Clipping affects the AXIS only — every reported statistic (mean, σ, Cpk, the box's own five-number summary) is computed from every value; nothing is excluded from the numbers, and the panel states how many points sit outside the visible range when some do. The box plot additionally has its own Log scale toggle, independent of the shared pair above (available once every plotted value is positive) — the histogram and trend charts do not offer one. - Correlation — a test-to-test correlation matrix and a die-level scatter plot, both stating the sample size the coefficients are computed over. Clicking a matrix cell drives the scatter plot onto that pair, where r and n for that pair are printed and update as you filter the legend.

In a gallery with more than one wafer, a Group by control appears whenever wafer metadata (lot, product, test program, temperature, split, or a custom field) actually varies across the loaded wafers — grouping pools or restricts each panel differently depending on what makes sense for that chart type. Histogram, correlation, and scatter also offer a Wafer picker to narrow from "all wafers pooled" down to one wafer at a time. Clicking a yield bar or box-plot row for one wafer opens that wafer's own map — a box-plot click opens directly on the test you were looking at.

Insights tab open on a single wafer, Overview sub-tab: yield and bin pareto, ring/quadrant yield, and per-test statistics — all computed from this wafer's own dies. The Distributions sub-tab has process capability, a test-value box plot and histogram; Correlation has a correlation matrix with scatter plot. In a gallery, Overview also gains a "Group by" control and per-wafer yield/box-plot rows.

Gallery Insights, Overview sub-tab: lot-wide yield by wafer (click a bar to open that wafer's map), hard/soft bin pareto, ring and quadrant yield, and pooled per-test statistics. The "‹ Gallery" tab returns to the card grid.

Distributions sub-tab: process capability (coloured by Ppk — green capable, orange marginal, red poor; tests without spec limits are muted and dashed), a per-wafer test-value box plot, and a value histogram. Clicking a capability box drives the box plot and histogram onto that test.

Correlation sub-tab: test-to-test Pearson correlation matrix (blue = positive, orange = negative; intensity = strength) and a die-level scatter plot coloured by hard bin. Clicking a matrix cell drives the scatter plot onto that pair.

Exporting a chart¶

Every chart panel has a camera button that saves the current view as a PNG at the displayed resolution. To get a clean full-resolution render, use the panel's expand (corner-arrows) button first to open it in the fullscreen modal, then click the camera button.

Each exported PNG includes a header strip above the chart with the panel title, source filename, wafer and die counts, the active test name (where applicable), and the time of export. The live card is unchanged — the header appears only in the saved file.

9. Reticle overlay¶

When reticle (stepper field) geometry is configured, the Reticle grid overlay draws the stepper field boundaries on the wafer. Each rectangle represents one exposure field from the lithography stepper — the group of dies exposed in a single step. This lets you correlate failure patterns with specific reticle positions — useful for identifying stepper field signatures, alignment drift, or mask defects.

Reticle-position findings in the Findings panel highlight the specific field positions that show elevated failure rates. Hovering any die also shows its Reticle (column, row) position — its location within its own stepper field — just below the die's coordinate in the tooltip.