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LGA — Land Grid Array Repair

The chapter's second package bends the area-array assumption from the other direction: the land grid array keeps the hidden field and throws away the balls. Under an LGA there are only flat plated lands — the solder that will become the joints does not ship on the package at all, and that single fact reorganizes the repair. Removal carries over from the BGA chapters nearly whole: the field is still hidden, the shield map still protects the neighbors, the lift is still zero-force at full liquidus. But what comes off the board is a package with flat lands, not stubs to reball — the reballing chapter's whole arc is simply not needed, and in its place stands a different craft: the bench must supply every microgram of the new joints' solder from the board side. That is the section's center. The mini-stencil meters paste onto the dressed site through apertures matched to the land pattern — the paste budget made mechanical — or, where no stencil fits the job, the tin-and-flux craft levels iron-applied solder into low, even caps the reflow can finish. Volume is the whole game: a starved site opens, a generous site bridges, and the package that receives the joints sits at almost no standoff — the flush seat that hides bridging, weakens the settle's authority, and closes the edge peek that BGA verification leaned on. So the verification ladder shifts its weight to the instruments that still reach: the meter through the fanout, the X-ray where the bench owns one, every claim bounded as the chapter before taught. Same hidden field, opposite solder logic — the LGA is the BGA's mirror, and this section teaches the bench to work in the mirror without breaking the glass.

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What You Will Learn

  • You will learn the land grid array — the area array with no balls, and the board-side solder logic that follows.
  • You will learn what carries from BGA removal unchanged — and the one gift the LGA gives back: no reballing.
  • You will learn the paste budget — volume as the craft's center, metered by mini-stencil or leveled by tin-and-flux.
  • You will learn the flush seat — near-zero standoff, weaker settle authority, tighter bridging margins, no edge peek.
  • You will learn LGA verification — the ladder re-weighted toward meter and X-ray, every claim still bounded.

What You Will Be Able To Do

  • You will be able to identify soldered-down LGA modules and distinguish them from their socketed cousins.
  • You will be able to remove an LGA with the BGA discipline and dress both sides of the joint flat.
  • You will be able to supply the board-side solder — stencil-metered paste or leveled tin — inside the paste budget.
  • You will be able to place and reflow against the flush seat's tighter margins.
  • You will be able to verify an LGA installation with the instruments that still reach, claims bounded.

Required Tools

  • The hot-air station and shield kit — LGA removal is BGA removal, and the removal law arrives intact
  • A mini-stencil matched to the land pattern — the paste budget made mechanical, where one exists for the module
  • Solder paste and a fine applicator — the board-side metal, metered rather than estimated
  • The fine iron and wick — the tin-and-flux alternative, and the land dressing on both sides of the joint
  • The meter and the fanout map — verification leans harder here, because the flush seat closes the edge peek

When NOT to Attempt This

Do not attempt this section if any of the following apply to you:

  • You are not comfortable working with small surface-mount components.
  • You have not completed the prerequisite sections for this skill.
  • You do not have the required tools in working condition.

Section Overview

The second bend in the chapter: the array keeps its hidden field and gives up its balls (csp-chip-scale-package-characteristics). The land grid array ships no solder. Flat plated lands under the package — every microgram of the future joints comes from the board side (stencil-and-flux-application). Removal arrives intact. Shield map, preheat, zero-force lift — BGA law whole; and what lifts off needs dressing, not reballing (bga-removal-with-hot-air). The mini-stencil meters the budget. Paste through apertures matched to the land pattern — volume made mechanical; tin-and-flux levels the alternative. The flush seat tightens everything. Near-zero standoff — weaker settle, hidden bridges, no edge peek. So verification re-weights. The meter through the fanout, X-ray where owned, claims bounded as the chapter taught (electrical-testing-of-bga-connections). No balls, board-side metal, metered volume, flush seat, bounded proof — the LGA entire.

Why This Matters

LGA modules are everywhere the radio is: Wi-Fi and Bluetooth modules, GPS receivers, MEMS microphones and sensors — the parts that make modern devices modern (csp-chip-scale-package-characteristics). This matters because the solder logic inverts: a bench that treats an LGA like a BGA reballs a package that needs no balls and starves a site that needed paste — the inversion is the section, and missing it wastes both crafts (stencil-and-flux-application). This matters because volume is unforgiving at zero standoff: the BGA's ball geometry absorbed small volume errors; the LGA's flush seat amplifies them — starved opens and generous bridges sit one aperture judgment apart (bga-removal-with-hot-air). It matters because the settle loses authority: less molten height means less collective pull, and the placement precision that BGA work could partly delegate to physics comes back to the hands. It matters because the edge peek dies at the flush seat: the perimeter read that anchored BGA verification closes to a dark seam, and the bench that cannot re-weight its ladder ships unverified work (electrical-testing-of-bga-connections). And it matters because the gift is real: no reballing — the removed LGA dresses flat and returns to service, and the bench that knows this quotes LGA rework honestly instead of pricing a phantom reball. Same field, mirrored solder — the inversion entire.

Required Prerequisites

Before starting this section, you should have completed:

  • Solder paste, fresh and refrigerated per its datasheet — the board-side metal; brought to room temperature before opening, because condensation in cold paste degrades the print, and expired paste separates into a budget nobody chose.
  • Tacky flux and liquid flux — the tin-and-flux alternative and the reflow's chemistry; the LGA site is fluxed with the same thin-even judgment the placement chapter taught.
  • Wick and fine solder — land dressing on both sides: the board site planed flat, the package lands leveled low.
  • Isopropyl alcohol and lint-free wipes — paste work is clean work; a smeared print is a budget already broken.
  • A donor router or IoT board with soldered LGA radio modules — the natural habitat: shielded, antenna-adjacent, and plentiful on scrap.
  • A donor board with MEMS microphones or sensors — the small end of the class, where the land count is low and the practice is honest.
  • A small-stencil kit or universal fine-pitch foil — aperture practice; where no stencil matches, the tin-and-flux exercise stands in.

Real-World Applications

The LGA repair is the radio bench's daily bread, and the board-side craft is what separates working modules from intermittent ones. A bench replacing a dead Wi-Fi module on an IoT gateway runs the whole inversion: BGA-discipline removal under the shield's neighborhood, both sides dressed flat, paste metered through the module's mini-stencil, and a reflow flown against the flush seat's tight margins (stencil-and-flux-application). A repairer chasing an intermittent MEMS microphone on a conference speakerphone finds the classic LGA fault — a starved joint at the module's corner, opened by the first thermal cycle — and the refit succeeds because the second paste budget was metered instead of guessed (electrical-testing-of-bga-connections). A fleet-shop technician swapping GPS receivers across tracker boards learns the gift early: removed modules dress flat and go back into rotation, no reballing arc, no sphere inventory — the LGA's turnaround is half the BGA's (bga-removal-with-hot-air). And a bench meeting its first LGA after the BGA chapters discovers what transfers and what inverts: the removal identical, the site dressing identical — and then the hands supplying every microgram of solder the package never carried (csp-chip-scale-package-characteristics). The confusions this prevents: a phantom reball quoted on flat lands, a paste budget guessed generous into bridges, a placement trusted to a settle with no height to work with, and a verification that peeked at a seam no light enters.

Common Challenges

  • The paste budget has no forgiving middle. Starved opens and generous bridges sit close together at zero standoff — the stencil's aperture is the judgment made mechanical, and freehand paste is a guess wearing a syringe (stencil-and-flux-application).
  • Tinned lands dome by default. An iron leaves solder in caps, not planes — the tin-and-flux craft levels them low and even, because a domed land rocks the seat and opens its neighbors (bga-removal-with-hot-air).
  • The seam hides its faults. Bridges form where no light enters and the package sits too low to show them — the meter and the X-ray inherit what the eye loses (electrical-testing-of-bga-connections).
  • Modules carry shields and antennas. The removal's neighborhood is crowded with formed metal and matched RF traces — the shield map discipline arrives from the BGA chapters already knowing this (csp-chip-scale-package-characteristics).

Safety Notes

Risk Level: Medium. Live heat over crowded neighborhoods — the full rework law, plus the paste's own handling rules.

  • Fume extraction from preheat — paste flux cooks earlier and dirtier than gel flux; the extractor runs before the first stage.
  • Paste hygiene — metal microspheres in flux: gloves or immediate washing, no food at the bench, expiry dates honored.
  • MEMS ports stay dry — bottom-port microphones and cavity sensors die from ingress: keep flux, paste, and cleaning fluid out of the port, and never ultrasonic-bath a MEMS part.
  • The removal law arrives whole — shield survey, bottom-side check, preheat, zero-force lift; an LGA removal is a BGA removal.
  • Power last, current-limited — the flush seat's hidden bridges are exactly what the meter must find before power can burn them.

Professional Tips Before Starting

  • Confirm the module is soldered, not socketed. The CPU-style LGA socket holds its package with spring contacts and a retention frame — no solder, no reflow, and a repair discipline this section does not teach — the soldered-down module is this section's patient (csp-chip-scale-package-characteristics).
  • Source the stencil before the removal. The budget tool decides the reinstallation plan — a job that starts before the stencil question is answered ends with freehand paste (stencil-and-flux-application).
  • Photograph the land pattern at removal. The site's geometry is the aperture check and the placement reference — the record costs seconds and anchors both crafts (bga-removal-with-hot-air).
  • Stage the verification before the reflow. Fanout map open, meter zeroed — the flush seat means the meter is the primary instrument, not the backup (electrical-testing-of-bga-connections).
  • Treat modules as moisture-sensitive. Overmolded radio and GPS modules carry MSL ratings like any laminate package — a salvaged module bakes per the moisture card before its refit reflow, or it popcorns at liquidus (stencil-and-flux-application).
  • Dress the package lands the moment it lifts. Flat tin and wick while the residue is fresh — an LGA that dresses flat is ready for its next board; that is the gift, taken on time.

The Mirror — No Balls, Board-Side Metal, Metered Volume

Recap and Frame

The chapter opened with the shrink; this section bends a different assumption — the array without its balls (csp-chip-scale-package-characteristics). The removal craft arrives whole. Shield map, preheat, molten-field check, zero-force lift — the BGA removal law transfers to the LGA untouched, because a hidden field under heat is a hidden field under heat (bga-removal-with-hot-air). The volume craft arrives trained. The reballing chapter taught apertures, metered spheres, and flux judgment — this section aims the same discipline at paste on the board side (stencil-and-flux-application). And the verification arrives bounded. The ladder and its instrument limits carry from the chapter before — this section re-weights the rungs for a package that closes the peek (electrical-testing-of-bga-connections). The frame is the mirror: everything learned, one inversion.

The Class and the Inversion — What an LGA Is

The land grid array is the area array stripped to its geometry: flat plated lands on the package underside, arranged in the same hidden grid, carrying no solder at all (csp-chip-scale-package-characteristics). The class divides at the socket. The socketed LGA — the CPU in its retention frame — presses lands against spring contacts and never sees solder; its repair is contact care and frame discipline, and it is not this section's patient. The soldered-down module is. Wi-Fi and Bluetooth radios, GPS receivers, MEMS microphones and environmental sensors — modules whose lands are reflowed to the board through paste that the assembly line printed (stencil-and-flux-application). The inversion follows from the missing balls. A BGA brings its own solder and the bench manages it; an LGA brings none — at repair time the bench supplies every microgram of the new joints from the board side, and the whole solder-volume decision moves from the package's spheres to the bench's judgment (bga-removal-with-hot-air). The gift follows too. What lifts off has flat lands, not sheared stubs — dressing is a wick pass and a flat tin, and the reballing arc simply does not apply. The trade's one niche exception is deliberate footprint conversion — balling an LGA part to seat it on a board laid out for its BGA sibling, an adaptation with its own volume math and not a refit; on the module's own footprint, flat lands are finished lands. Geometry, divide, patient, inversion, gift — the class entire. An LGA is a BGA that outsourced its solder to whoever owns the board — and at repair time, that is you.

The Budget — Metering the Board-Side Metal

Volume is the LGA craft's center, and the section's one absolute is that volume is metered, never guessed (stencil-and-flux-application). The mini-stencil is the first choice. A thin foil with apertures matched to the land pattern, aligned over the dressed site, paste squeegeed through and the foil lifted clean — the budget made mechanical, each land receiving what its aperture allows and nothing more. The aperture check comes first. Foil against the photographed land pattern before any paste: openings matched to lands, no bridged apertures, no missing ones — a stencil that fails the check is a budget error waiting for heat (csp-chip-scale-package-characteristics). Tin-and-flux is the honest fallback. Where no stencil fits the job: each land tinned with the fine iron, then leveled — wick passes and flux until every cap sits low and even — and the reflow flown on tacky flux alone, the leveled tin supplying the metal (bga-removal-with-hot-air). Level is the fallback's law. An iron leaves domes; domes rock the seat; a rocked seat opens the far corner — the leveling pass is not cosmetic, it is the seat's geometry being decided in advance. Both crafts end at the same judgment. Enough metal to wet every land into a full joint; little enough that a package at zero standoff cannot squeeze neighbors together — starved opens, generous bridges, metered works (electrical-testing-of-bga-connections). Stencil, check, fallback, level, judgment — the budget entire. The assembly line printed this site once with a machine's precision; the bench's job is to match that precision with a foil, an iron, and restraint.

The Seat and the Proof — Flush Margins, Re-Weighted Ladder

The LGA seats flush, and the flush seat re-prices everything downstream (csp-chip-scale-package-characteristics). The settle loses height. Less molten volume under the package means less collective pull — the self-alignment that recovered BGA placements works here too, but with a shorter reach, and placement accuracy takes back what the physics gives up (stencil-and-flux-application). The placement runs the full discipline. Witness where orientation matters, straight descent, no sliding — the placement chapter's laws, applied with less forgiveness behind them (bga-removal-with-hot-air). The reflow watches a smaller tell. The LGA's settle read is subtle — a slight level-out rather than a visible sink — and the stillness law through the freeze is unchanged. The seam hides what the peek used to catch. At near-zero standoff, bridges form in the dark and the edge peek that anchored BGA verification closes — a flush perimeter shows a seam, not joints. So the ladder re-weights. The meter through the fanout becomes the primary instrument; X-ray reads the bridges and voids the seam conceals; power waits, current-limited, behind both — and every claim is written bounded, naming its instrument, exactly as the chapter before taught (electrical-testing-of-bga-connections). Height, discipline, tell, seam, proof — the seat entire. The LGA gives the bench less to see and the same amount to prove — the difference is made up with instruments, not confidence.

Common Mistakes

  • Reballing an LGA. Flat lands are the package's finished state, not a missing feature — building balls onto an LGA misspends the reballing craft and doubles the joint's volume budget before the board side adds its own (stencil-and-flux-application).
  • Guessing the paste. Freehand syringe work 'about this much per land' — the budget is metered by aperture or leveled tin; the guess is starved on one land and generous on the next, and the flush seat punishes both (csp-chip-scale-package-characteristics).
  • Leaving tinned lands domed. The iron's natural cap looks tidy and rocks the seat — domes are leveled low and even before any placement, because the seat's geometry is decided at the tinning bench (bga-removal-with-hot-air).
  • Trusting the edge peek. A flush seam reads clean at every angle — the LGA perimeter shows nothing; the meter and the X-ray own this verification (electrical-testing-of-bga-connections).
  • Treating the socketed cousin as the same repair. A CPU socket's bent spring contact is a mechanical repair with its own discipline — paste has no place in a socket, and this section's craft stops at the soldered-down module.

Troubleshooting Guidance

  • Open joint after reflow — the classic starved-budget signature, usually at a corner or along one edge: map the opens against the paste record; a starved print re-runs the budget, a rocked seat from domed tin re-runs the leveling, and the distinction is visible in which lands opened (stencil-and-flux-application).
  • Bridges found by meter or X-ray — the generous-budget signature, hidden under the flush seam: the module comes off, both sides dress flat, and the second budget is metered smaller — bridges at zero standoff are removal-and-redo, not rework-in-place (electrical-testing-of-bga-connections).
  • Module rocks before reflow — the seat check catching domed tin or debris: lift on the pen, inspect the site under grazing light, re-level or re-clean — a rock found loose costs a minute; found after reflow it costs the joint map (bga-removal-with-hot-air).
  • Stencil will not sit flat on the site — dressing residue or masked-area interference: re-plane the site and check the stencil against the photographed pattern; a foil that bridges apertures over a proud spot prints a budget error in the exact shape of the problem (csp-chip-scale-package-characteristics).

Verification & Testing Methods

Confirm your LGA discipline before calling this section complete:

  • [ ] I can identify a soldered-down land grid array, rule out the socketed cousin, and state the inversion — flat lands, board-side solder, no reball ever.
  • [ ] I can remove an LGA under the full BGA removal law and dress both sides of the joint flat.
  • [ ] I can meter the board-side budget — mini-stencil apertures checked against the pattern, or tin leveled low and even.
  • [ ] I can place and reflow against the flush seat — full placement discipline, subtle settle tell, stillness through the freeze.
  • [ ] I can verify with the instruments that reach — meter primary, X-ray where owned, power last and limited — claims bounded.

Then try the practice exercises below — removal, budget, and refit on donor modules; scenarios differ from the quiz.

Practice Exercises

  1. Read the site and plan the budget (6 minutes, donor board cold). Pick one soldered LGA module, confirm it is soldered rather than socketed, photograph its neighborhood and shields, and write the budget plan: stencil available or tin-and-flux fallback, aperture check notes, and the verification map the flush seat will demand (csp-chip-scale-package-characteristics).
  2. Remove and dress both sides (7 minutes, under the full removal law). Run the BGA removal discipline — shields, preheat, molten-field check, zero-force lift — then dress the board site flat and the module's lands low: wick, flat tin, and the leveling passes that decide the future seat (bga-removal-with-hot-air).
  3. Meter the budget and refit (7 minutes, the dressed site). Print through the mini-stencil or level the tinned site, judge the volume against the starved-opens/generous-bridges line, place with full discipline, and fly the reflow — watching for the LGA's subtle level-out and holding stillness through the freeze (stencil-and-flux-application).
  4. Verify what the seam hides (5 minutes, the cooled refit). Run the re-weighted ladder: the seam inspected for what little it shows, then the meter through the fanout on every reachable net, and the claims written bounded — including the honest line about what only an X-ray could confirm (electrical-testing-of-bga-connections).

These core steps — the budget plan, the both-sides dressing, the metered refit, and the seam-blind verification — are tested in the Chapter Quiz at the end of this chapter, where a score of 80% is required to continue.

Key Takeaways

  • The land grid array is the area array with no balls — flat plated lands, every microgram of the joints supplied from the board side, and the whole reballing arc replaced by a volume judgment (csp-chip-scale-package-characteristics).
  • Removal transfers whole — shield map, preheat, zero-force lift — and the gift comes at the lift: flat lands dress with a wick pass, and the module is ready for its next board (bga-removal-with-hot-air).
  • The mini-stencil makes the paste budget mechanical — apertures matched to the land pattern, checked before paste, with leveled tin-and-flux as the honest fallback (stencil-and-flux-application).
  • The flush seat re-prices the downstream: weaker settle authority, bridges hidden in the seam, and an edge peek closed to nothing.
  • Verification re-weights to the instruments that reach — meter primary, X-ray where owned, power last and current-limited — every claim bounded by what made it (electrical-testing-of-bga-connections).

Skills Learned

After completing this section, you can:

  • Identify soldered-down LGA modules, distinguish them from socketed packages, and scope the repair correctly.
  • Remove an LGA under the full BGA removal law and dress both sides of the joint to flat.
  • Meter a board-side solder budget by mini-stencil or leveled tin, inside the starved/generous margins.
  • Place and reflow an LGA against the flush seat's reduced forgiveness.
  • Verify a flush-seated installation with a re-weighted, bounded ladder.

Glossary Additions

New terms introduced in this section:

  • land grid array — the area-array package that ships no solder: flat plated lands on the package underside in the same hidden grid a BGA hides, with the joints' entire metal supplied from the board side at assembly — and at repair. The class divides at the socket: socketed LGAs press lands against spring contacts and never see solder, while the soldered-down modules this craft serves — radio modules, GPS receivers, MEMS microphones and sensors — are reflowed onto printed paste. The repair inversion follows: removal matches BGA law exactly, but reinstallation means the bench meters every microgram of new solder, and the removed package needs only flat dressing — never a reball.
  • mini-stencil — the small aperture foil that makes an LGA's board-side solder budget mechanical: openings matched to the site's land pattern, aligned over the dressed site, paste squeegeed through and the foil lifted clean, so each land receives what its aperture allows and nothing more. The stencil is checked against the photographed land pattern before any paste — matched openings, none bridged, none missing — because a bad foil prints a budget error in the exact shape of the site. Where no stencil fits the job, the fallback is tin-and-flux: iron-tinned lands leveled low and even, with the reflow flown on flux alone.
  • flush seat — the near-zero standoff at which an LGA sits: less molten height than any BGA, and every consequence follows from the missing millimeter. The settle keeps its law but loses reach, so placement accuracy carries more of the outcome; bridges form in a seam no light enters; and the edge peek that anchored BGA perimeter verification closes entirely — a flush perimeter shows a seam, not joints. Verification answers by re-weighting: the meter through the fanout becomes the primary instrument, X-ray reads what the seam conceals, and power arrives last, current-limited, behind claims bounded by the instruments that made them.

Suggested Next Sections

Must read next:

  • PoP — Package-on-Package Theory — Section 6.3 stacks the arrays: two hidden fields, one on top of the other, and the failure geometry that stacking invents — at Professional depth.

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