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Pad Planarity and Preparation

Three benches in a row have leaned on the same quiet phrase — the site dressed flat, proven, and photographed — and this section finally pays that phrase its own wages, because at fine pitch the site is not preparation for the joint: it is half of it. The discipline splits into a craft and a verdict. The craft is dressing: old solder wicked from the land pattern with the wick matched to the pad class — fine braid in single passes on perimeter pads, wide braid with a real heat budget on thermal pads whose vias drink like the planes they tie into — always with fresh flux, always iron-on-wick and never bare tip on bare pad, because over-wicking is how dressing becomes the pad-repair bench's next customer. The surfaces have personalities the craft must read: HASL arrives undulating from the factory and will never read dead flat — its gentle waves are acceptable and its solder mounds are not — while ENIG reads flat and bright but rewards a lighter touch, and the read names the finish before the wick chooses its ambitions. The verdict is planarity: the dressed site under magnification with light raked low across it, every residual mound showing as a dome against its neighbors, the gentle straightedge confirming only what the light already suggested — because a bump left proud rocks whatever lands on it, and a rocked package solders some of its joints and abandons the rest. Between craft and verdict sit the supporting disciplines: cleaning that takes the flux residue off before any read pretends to be honest, the leveling choice — thin fresh tinning for iron work, flat near-bare copper for paste work — made deliberately per the job ahead, and the damage triage that routes lifted copper and torn mask to the pad-repair bench instead of soldering over either. The section ends where every site must: at the readiness verdict — flat, clean, intact, bright, photographed — the formal gate this chapter's remaining benches and the BGA chapters beyond will refuse to work without.

AdvancedMedium Risk23 min read

What You Will Learn

  • You will learn why the site is half the joint — the two planarities, package and board, that must both be flat for anything to close.
  • You will learn the dressing craft per pad class — fine braid on perimeter pads, wide braid and heat budget on thermal pads, always iron-on-wick with fresh flux.
  • You will learn the surface personalities — HASL's honest undulation versus its dishonest mounds, ENIG's flat brightness and lighter touch.
  • You will learn the planarity verdict — grazing light as the primary read, domes against neighbors, the straightedge confirming only.
  • You will learn the readiness gate — flat, clean, intact, bright, photographed — and the damage triage that routes injuries to the pad bench.

What You Will Be Able To Do

  • You will be able to read a site's finish and pad classes and choose the dressing plan before the iron heats.
  • You will be able to dress any pad class flat — single passes on fine pads, budgeted heat on thermal pads — without feeding the pad bench.
  • You will be able to issue planarity verdicts under grazing light and know HASL's waves from its mounds.
  • You will be able to make the leveling choice deliberately — tinned for iron work, near-bare flat for paste work.
  • You will be able to run the readiness gate and triage damage honestly to the pad-repair bench.

Required Tools

  • Solder wick in at least two widths, fresh and rosin-carried — the dressing's blade
  • Gel flux and a temperature-controlled iron — the wick works only as wet as its flux
  • A microscope with a movable light source — the planarity verdict lives at low angles
  • A gentle straightedge — confirming only, never dragged across dressed pads
  • Isopropyl and lint-free swabs — no read is honest through flux residue

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

Three benches leaned on one quiet phrase — dressed flat, proven, photographed — and this section pays the phrase its wages, because at fine pitch the site is half the joint (qfn-package-rework-challenges-and-technique). The two planarities frame everything. A joint closes only when the package's coplanarity meets the board's site planarity — and the bench controls exactly one of them (dfn-and-small-thermal-pad-packages). The craft is site dressing per pad class. Fine braid in single passes on perimeter pads, wide braid with a real heat budget on thermal pads, always fresh flux, always iron-on-wick — because over-wicking is how dressing feeds the pad bench (smd-desoldering-wick-and-iron). The surfaces have personalities. HASL undulates honestly from the factory and mounds dishonestly after rework; ENIG reads flat and bright and rewards a lighter touch. The verdict reads under grazing light. Every residual mound a dome against its neighbors, the straightedge confirming only what the light suggested. And the gate closes the section. Flat, clean, intact, bright, photographed — with lifted copper and torn mask triaged to the pad-repair bench, never soldered over (smd-and-fine-pitch-pad-repair). Two planarities, the craft, the personalities, the verdict, the gate — the site bench entire.

Why This Matters

Every rework in this volume lands on a site somebody prepared, and the preparation decides more outcomes than the placement does (qfn-package-rework-challenges-and-technique). This matters because the site is the half of the joint the bench controls: package coplanarity ships from the factory; site planarity is manufactured at this bench, every job, and a bump left proud rocks whatever lands on it — some joints made, the rest abandoned on a diagonal (dfn-and-small-thermal-pad-packages). This matters because dressing injuries are self-inflicted pad-bench referrals: the wick dragged dry, the bare tip scrubbed on a bare pad, the fifth pass where one would do — fine-pitch copper lifts at exactly the enthusiasm level a hurried bench brings, and the microsurgery that follows costs ten times the patience that would have prevented it (smd-and-fine-pitch-pad-repair). It matters because the surface finishes lie differently: HASL's factory waves read as failure to benches that never learned them, and its rework mounds read as acceptable to benches that never learned the difference — the verdict is only as good as the reader's fluency in the surface (smd-desoldering-wick-and-iron). It matters because the leveling choice is invisible until it is wrong: paste printed over domed tinning slumps and bridges; iron work on stripped-bare copper fights oxidation — the choice is made per the job ahead, deliberately. And it matters because the gate scales: the BGA chapters ahead will place hundreds of joints blind onto sites this discipline prepares — the readiness verdict is the last moment anyone can see what the balls will land on. Manufacture the flat, read it honestly, gate every site — and the placements that follow inherit foundations instead of gambles.

Required Prerequisites

  • Fresh rosin-carried wick, stored sealed — to cut cleanly instead of scorching — stale wick is the craft's quiet saboteur (smd-desoldering-wick-and-iron)
  • Gel flux in quantity — to keep every wick pass wet, because the dry pass is the pad-lifter (smd-and-fine-pitch-pad-repair)
  • Isopropyl and lint-free swabs — to strip residue before any read claims honesty (qfn-package-rework-challenges-and-technique)
  • Fresh solder for deliberate re-tinning — to level dressed pads for iron work when the job ahead wants tin
  • Donor boards with freshly stripped sites from the last three sections' exercises — to dress real removal aftermath instead of staged examples (dfn-and-small-thermal-pad-packages)
  • A HASL board and an ENIG board side by side — to learn the two personalities under the same light (smd-desoldering-wick-and-iron)
  • A microscope with a movable light — to drill the grazing read until domes announce themselves (qfn-package-rework-challenges-and-technique)
  • A sacrificial site to over-wick deliberately — to feel where enthusiasm lifts copper, once, on a board nobody loves (smd-and-fine-pitch-pad-repair)
  • The bench camera — to close every readiness gate with its photograph

Real-World Applications

The site bench is invisible in every success and implicated in every rocked package. A technician dressing a tablet's stripped QFN site before the replacement lands works the pad classes separately — fine braid in single fluxed passes across the perimeter, wide braid with a real heat budget on the thermal pad — and the site passes its grazing read flat, the replacement settling square because the foundation gave it no choice (qfn-package-rework-challenges-and-technique). A bench reading a router board's HASL surface after a removal accepts the factory's gentle waves and rejects the two rework mounds the light shows as domes — the fluency that neither re-dresses acceptable undulation nor blesses proud solder (smd-desoldering-wick-and-iron). A repair shop tracing a returned rework — a regulator soldered beautifully on two corners and open on the others — finds the culprit in its own process photos: a residual mound visible in the naked-site shot nobody read, the rocked package's diagonal written in the record before the placement ever happened (dfn-and-small-thermal-pad-packages). And a technician whose wick pass comes up with copper glinting against the tinned braid stops mid-dress, photographs the torn pad, and routes the job to the pad-repair bench with the honest conversion — the referral that costs a customer conversation now instead of a failed joint later (smd-and-fine-pitch-pad-repair). The failures this prevents: a package rocked on a mound the light would have shown, a HASL board re-dressed to death chasing a flatness it never had, paste printed over domed tinning and bridged at reflow, and a lifted pad soldered over because the dressing that caused it never stopped to look.

Common Challenges

  • The wick tempts repetition. One more pass always promises perfect — the difficulty is the one-pass-then-inspect rhythm, because passes three through five are where pads lift (smd-desoldering-wick-and-iron).
  • The surfaces need separate fluency. HASL's waves are healthy and its mounds are not; ENIG's flatness is real and its fragility too — the difficulty is reading each finish by its own standard instead of one imagined ideal (qfn-package-rework-challenges-and-technique).
  • The gate feels like ceremony on easy jobs. A big-pitch site barely needs the checks — the difficulty is running the gate anyway, because the habit that lapses on easy sites is absent on the BGA sites that cannot forgive it (smd-and-fine-pitch-pad-repair).

Safety Notes

Risk Level: Medium. Iron work, solvents, and fine copper — the site bench's hazards are the volume's standing ones, aimed at the board's most vulnerable feature.

Professional Tips Before Starting

  • Cut wick fresh for every site. The oxidized end that worked yesterday scorches today — an inch sacrificed per job is the cheapest consumable discipline on the bench (smd-desoldering-wick-and-iron).
  • Read the finish before the first pass. HASL or ENIG decides the flatness standard and the touch — ten seconds of looking calibrates the whole dress (qfn-package-rework-challenges-and-technique).
  • Keep the light on a boom. The grazing read needs angles the ring light cannot make — a movable source is the verdict's real instrument (dfn-and-small-thermal-pad-packages).

The Site Bench — Two Planarities, The Craft, The Verdict, The Gate

Recap and Frame

Three benches borrowed this section's discipline in advance; now it gets built properly under its own name (qfn-package-rework-challenges-and-technique). The wick craft arrives from Volume 3. Braid, flux, and the iron-on-wick rule — taught for removal, promoted here to site manufacture, where the standard is no longer 'solder gone' but 'foundation flat' (smd-desoldering-wick-and-iron). The pad bench stands ready behind every mistake. Volume 4's microsurgery inherits whatever this bench injures — and the stop rule exists so that inheritance stays rare (smd-and-fine-pitch-pad-repair). The scaled sites arrive from last section. Thermal pads that dominate tiny bellies, perimeter pads in fractions of a millimeter — the smallest real estate yet, dressed under magnification or not at all (dfn-and-small-thermal-pad-packages). What is new is the promotion. Site work as a discipline with its own craft, its own verdict, and its own gate — because the chapter's last section and the BGA chapters beyond will place blind onto whatever this bench certifies. Hold the frame — craft promoted, injuries triaged, verdict formalized — and every placement after this inherits a foundation.

The Two Planarities — Why the Site Is Half the Joint

A solder joint is two surfaces agreeing to meet, and the bench controls exactly one of them (dfn-and-small-thermal-pad-packages). The package brings its coplanarity. Leads formed to sit in one plane, balls sphered to one height, bellies molded flat — tolerances the bench inspects and only rarely repairs: a bent lead re-formed, a ball field rebuilt at the reballing bench ahead — never improved in the course of a placement, and read on the replacement part before it ever approaches the board (qfn-package-rework-challenges-and-technique). The board brings its site planarity. The land pattern's collective flatness — every pad at its intended height, no residual solder standing proud — and unlike the package's half, this one is manufactured at the bench, every job, by the dressing. The failure mode is the rock. A mound under one corner tilts the package across its diagonal: the near joints close rich, the far ones close starved or never, and the assembly passes every glance while failing half its connections (smd-and-fine-pitch-pad-repair). The stakes scale with pitch and blindness. A coarse QFP forgives what a fine one cannot; a QFN hides what a QFP would show; and the BGA chapters ahead stack hundreds of joints on sites nobody will see again after placement (smd-desoldering-wick-and-iron). Package half read, board half manufactured, the rock understood, the stakes scaled — the frame entire. The bench cannot flatten the part — so the site carries the whole burden of agreement.

The Craft — Dressing by Pad Class and Personality

Dressing is wick work with a manufacturing standard, and the craft divides by what the pad is and what covers it (smd-desoldering-wick-and-iron). Perimeter pads take the fine braid. Narrow wick matched to the row, fresh flux under it, the iron pressing wick to pad in single passes — one pass, inspect, and only then another — because fine copper lifts as heat and drag accumulate faster than progress (smd-and-fine-pitch-pad-repair). Thermal pads take width and budget. Wide braid, more flux, and a real heat budget — the pad ties into the plane and drinks like one, and starving the pass just smears — with the via field watched for solder pulled through or out (qfn-package-rework-challenges-and-technique). The iron never meets bare copper. Iron on wick, wick on solder — the tip that scrubs a stripped pad burns mask and lifts feet, and the rule has no exceptions at any pitch. HASL reads by its own standard. Hot-air-leveled surfaces arrive gently undulating from the factory — that wave is the finish, not a fault, and chasing it flat strips the pad; the dressing removes rework mounds and leaves the factory's geography alone (dfn-and-small-thermal-pad-packages). ENIG reads flat and rewards restraint. The gold-over-nickel surface is genuinely planar and thin — a lighter iron, fewer passes — because the gold over any wetted pad already dissolved into its first joint, and what the restraint protects is the thin nickel beneath, which scrubbing oxidizes and no bench replates; any bright gold still showing at the site's edges is left exactly as found. Fine and single, wide and budgeted, iron-on-wick always, HASL's waves respected, ENIG touched lightly — the craft entire. Dressing ends when the site is flat, not when the wick is tired.

The Verdict — Grazing Light and Honest Flatness

The dressed site faces its verdict under light, and the verdict's instrument is the angle (qfn-package-rework-challenges-and-technique). Grazing light is the primary read. The source brought low, raking across the land pattern under magnification — flat pads read as one continuous brightness while every residual mound throws a dome's shadow signature against its neighbors, visible at fractions the eye would never catch top-down (dfn-and-small-thermal-pad-packages). The straightedge confirms only. Laid gently across where the light suggested trouble — never dragged, never trusted alone — the touch that turns a suspicion into a verdict without scratching mask or plating (smd-and-fine-pitch-pad-repair). The read is finish-fluent. HASL's gentle waves pass; its mounds fail; ENIG's flatness is the standard it actually meets — the same light, different acceptances, and the reader who learned only one surface misjudges the other (smd-desoldering-wick-and-iron). Residue disqualifies the read. Flux films throw their own shadows and gloss — the isopropyl pass comes before the verdict, every time, because no read through residue is honest. The leveling choice follows the verdict. Iron work ahead wants a thin fresh tinning — deliberate, even, domeless; paste work ahead wants the site near-bare and flat, because hand-applied tin domes taller than any factory coating and paste printed over domes slumps and bridges — flat is the requirement, near-bare is how a hand bench reliably gets it — chosen per the next job, not by habit. Low light, gentle steel, finish fluency, clean surface, deliberate leveling — the verdict entire. The light does the measuring; the bench's job is to put it at the angle where solder cannot lie.

The Gate — Ready to Receive, or Routed Away

Every site ends at the same gate, and the gate has five checks and two exits (smd-and-fine-pitch-pad-repair). Flat under the grazing read. No domes, no proud remnants — the finish's own geography and nothing else. Clean of every residue. Flux stripped, swab lint gone, the surface ready to be photographed without excuses (qfn-package-rework-challenges-and-technique). Mask intact to its edges. No curls, no burns, no scratches into the dam between pads — because mask injuries become bridges at reflow (smd-desoldering-wick-and-iron). Pads bright and continuous. Full footprints, no torn corners, no dull scrubbed patches — the copper's whole story readable at magnification. Photographed naked. The record's foundation shot — the proof of what the placement received, and the answer to every later question about what went wrong or did not (dfn-and-small-thermal-pad-packages). The second exit is the honest one. Any check failed by damage — lifted copper, torn mask, a pad gone dull and thin — stops the job at the photograph and routes to the pad-repair bench: the conversion quoted at the evidence, exactly as the volume has always priced honesty, because soldering over an injury buys one appointment and pays for two. Flat, clean, intact, bright, photographed — or routed away — the gate entire. No site receives a part without passing; the BGA chapters will thank this habit before the volume ends.

Common Mistakes

  • Scrubbing bare pads with a bare tip. The solder is gone but the iron keeps working — iron on wick only; the tip that touches stripped copper burns mask and lifts feet (smd-desoldering-wick-and-iron).
  • Chasing HASL flat. The factory's waves treated as rework mounds — the finish's geography is the standard; only proud solder fails the read (qfn-package-rework-challenges-and-technique).
  • Reading through residue. The verdict issued over flux gloss — isopropyl before the light, every time, because films throw shadows that lie both ways (dfn-and-small-thermal-pad-packages).
  • The fifth pass. One more will make it perfect — the passes after the first are where pads lift, because heat and drag accumulate faster than progress; one pass, inspect, decide (smd-and-fine-pitch-pad-repair).
  • Soldering over the injury. The lifted corner flattened with solder and hope — damage stops the job at the photograph and routes to the pad bench; covered injuries fail at the customer's desk.

Troubleshooting Guidance

The site bench troubleshoots its own craft in order: finish, flux, pass, light, gate. If the wick smears instead of cutting: the pass is dry or the wick is stale — fresh flux under fresh braid, and the heat budget re-read for the pad class (smd-desoldering-wick-and-iron). If a thermal pad will not come flat: the budget is short — the plane is drinking the pass; more preheat, wider braid, and patience over repetition (qfn-package-rework-challenges-and-technique). If the grazing read keeps flagging the same spot: believe the light — re-dress that spot alone with a single targeted pass, then re-read; the straightedge confirms if doubt survives (dfn-and-small-thermal-pad-packages). If copper glints in the braid or mask curls at an edge: the stop rule — photograph, halt the dressing, route to the pad bench with the conversion honest (smd-and-fine-pitch-pad-repair). If paste work keeps bridging on sites that passed: the leveling choice — domed tinning under the print; re-dress to near-bare flat for paste jobs. If the gate keeps failing sites on cleanliness: the swab discipline slipped — fresh isopropyl, fresh swabs, and the read only after the flash-off. The throughline: every site problem is visible under the right light before it is a joint problem after — the bench that reads early never meets the rocked package.

Verification & Testing Methods

Confirm the site bench end to end before the chapter's last section builds on it:

  • [ ] I read finish and pad classes before the iron heats, and choose the dressing plan — braid widths, budgets, passes — from the read.
  • [ ] I run site dressing to the craft — fresh flux, iron-on-wick, single passes inspected — and stop at the first sign of injury.
  • [ ] I issue site planarity verdicts under grazing light with finish fluency — HASL's waves accepted, mounds failed, ENIG's flatness held to its own standard.
  • [ ] I make the leveling choice deliberately per the job ahead — thin even tinning for iron work, near-bare flat for paste.
  • [ ] I run the readiness gate on every site — flat, clean, intact, bright, photographed — and route damage to the pad-repair bench at the photograph.

Then try the practice exercises below — donor-site bench work throughout; scenarios differ from the quiz.

Practice Exercises

  1. Read two finishes cold (6 minutes, HASL and ENIG donors, microscope with movable light). Under grazing light, map each board's personality — HASL's factory waves versus any rework mounds, ENIG's flatness and any scrubbed dull patches — and log which features would pass and fail a planarity verdict on each, building the finish fluency the craft assumes (smd-desoldering-wick-and-iron).
  2. Dress a stripped site to the craft (7 minutes, a donor site from an earlier exercise, wick in two widths). Read the site's finish and pad classes and log the plan — braid widths, budgets, expected passes — before the iron heats, then work the pad classes separately — fine braid in single fluxed passes on the perimeter, wide braid with a budgeted pass on the thermal pad — inspecting after every pass, and log the pass count each class actually needed against the enthusiasm that wanted more (smd-and-fine-pitch-pad-repair).
  3. Issue the verdict and level deliberately (7 minutes, the dressed site, isopropyl, fresh solder). Strip residue, run the grazing read, confirm any suspect spot with the gentle straightedge, then make the leveling choice twice: tin half the site thin and even for iron work, leave half near-bare flat for paste — and read both halves under the light to see what each job would receive (qfn-package-rework-challenges-and-technique).
  4. Run the gate — both exits (5 minutes, two sites: the dressed one and a damaged donor). Walk the five checks on the healthy site through to its naked photograph, then walk the damaged donor honestly to the second exit — the injury photographed, the pad-bench referral written as the conversion a customer would hear — closing with one line on why soldering over it would have cost more (dfn-and-small-thermal-pad-packages).

These core steps — the finish read, the classed dressing, the lit verdict, and the two-exit gate — are tested in the Chapter Quiz at the end of this chapter, where a score of 80% is required to continue.

Key Takeaways

  • A joint is two surfaces agreeing to meet, and the bench controls one: site planarity is manufactured at the dressing, every job, while the package's coplanarity only gets inspected (dfn-and-small-thermal-pad-packages).
  • Site dressing is wick craft with a manufacturing standard — fresh flux always, iron-on-wick always, single passes inspected, budgets per pad class — and it ends when the site is flat, not when the wick is tired (smd-desoldering-wick-and-iron).
  • The surfaces have personalities: HASL's factory waves are the finish and its rework mounds are the fault; ENIG is genuinely flat and rewards restraint — the verdict is only as good as the reader's finish fluency (qfn-package-rework-challenges-and-technique).
  • The verdict reads under grazing light — domes shadow against their neighbors at angles top-down inspection never catches — with the straightedge confirming gently and residue stripped before any read claims honesty.
  • The gate has five checks and two exits — flat, clean, intact, bright, photographed, or routed to the pad-repair bench at the evidence — because soldering over an injury buys one appointment and pays for two (smd-and-fine-pitch-pad-repair).

Skills Learned

  • You can now read a site's finish and pad classes and choose the dressing plan before the iron heats.
  • You can now dress any pad class flat — single passes on fine pads, budgeted heat on thermal pads — without feeding the pad bench.
  • You can now issue planarity verdicts under grazing light and know HASL's waves from its mounds.
  • You can now make the leveling choice deliberately — tinned for iron work, near-bare flat for paste work.
  • You can now run the readiness gate and triage damage honestly to the pad-repair bench.

Glossary Additions

  • site dressing — the manufacture of a flat, clean land pattern from a stripped rework site: old solder wicked away with the braid matched to the pad class — fine wick in single inspected passes on perimeter pads, wide wick with a genuine heat budget on plane-tied thermal pads — always over fresh flux, always iron-on-wick and never bare tip on bare copper. Dressing is promoted from cleanup to manufacture because the site is half of every joint that will form on it, and the craft carries a stop rule with no exceptions: copper glinting against the tinned braid, mask curling, or a pad shifting under the pass halts the work at a photograph and routes the job to the pad-repair bench — because dressing that damages has not prepared a site, it has created a patient.
  • grazing light — the low-angle illumination that makes solder height visible: a movable source brought down until light rakes across the land pattern under magnification, rendering flat pads as continuous brightness and betraying every residual mound as a dome shadowed against its neighbors — height differences readable at fractions the eye never catches top-down. Grazing light is the planarity verdict's primary instrument, with the gentle straightedge confirming only what the light already suggested; its honesty depends on a clean surface, since flux films gloss and shadow in ways that lie in both directions, and its readings are finish-fluent — HASL's gentle factory undulation passes, proud rework solder does not, and ENIG is held to the genuine flatness it ships with.
  • site planarity — the collective flatness of a land pattern: every pad at its intended height with no residual solder standing proud, the board-side half of the agreement every solder joint is. A joint closes only when the package's coplanarity — manufactured at the factory, merely inspected at the bench — meets a site whose planarity the bench itself manufactures at the dressing; the failure mode of the miss is the rock, a mound under one corner tilting the package across its diagonal so near joints close rich and far joints close starved or never, on an assembly that passes every casual glance. Site planarity is verified under grazing light before any placement, and its verdict scales in consequence with pitch and blindness — culminating in the ball-grid chapters, where hundreds of joints land on a site nobody will ever see again.

Suggested Next Sections

Must read next:

  • Advanced Inspection After Rework — Section 1.5 closes the chapter by training the eyes the volume will trust from here on: fillet reading as a formal skill, wetting judgment across finishes, magnification discipline, and the electrical verification that outranks every optical opinion — the inspection bench the hidden-package chapters will lean on completely.

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