Section Overview
You have read the site and graded it (9.3); now you prepare it — turning those pads into a clean, flat, coplanar, defect-free surface a new part can actually seat and solder on. A perfect assessment does not make a joint: preparation does, and it comes before any new part touches the board. The sequence is straightforward. First, strip the site: wick off every bit of the old joint's solder down to flat pads or bare copper (solder wick, 6.6), clean away all flux residue, and — the one that hides — remove every trace of any low-melting-point alloy residue left from a low-melt removal, which is invisible on a clean-looking pad but makes the next joint weak (alloy compatibility, 9.2). Second, repair the damage the assessment flagged: pad repair re-bonds a partly-lifted pad or, for a pad torn off entirely, replaces it or jumpers the new lead's position to the trace — restoring the copper the new part needs. Third, level the pads: leave them with a thin, even coat of solder or clean copper, and for fine-pitch and especially BGA sites use solder leveling — wicking and reflowing the residual solder so every pad is flat and the same height (coplanarity) — because uneven pads make a new part sit crooked and solder into bridges and opens. Fourth, clear obstructions: any conformal coating over the work area must be removed before soldering, both because it blocks wetting and because it gives off harmful fumes when heated; clear adhesive, potting, or debris too. Finally, flux and verify: apply fresh flux (and solder paste if the install uses it, 8.5), then confirm the pads are clean, flat, coplanar, repaired, and residue-free — the site is ready only when it matches the good-site standard (9.3). Strip, repair, level, de-coat, flux, and verify — and the site is ready for a new part.
Why This Matters
Site preparation is the step that actually builds the foundation the new joint stands on — assessment only told you what was wrong; prep is where you make it right. This matters because a clean, flat, coplanar site is what lets a new part solder correctly: leftover solder blobs, contamination, a lifted pad, or uneven pad heights each guarantee a bad joint, so removing all of them is what makes a good install possible. It matters because the low-melt-residue trap is unforgiving: bismuth left on a pad from a low-melt removal is invisible and ruins the next joint, so the cleaning step here is the only thing standing between a low-melt removal and a brittle repair (alloy compatibility). It matters because pad repair turns a scrapped board into a fixable one: a torn or lifted pad flagged in assessment is not the end — repaired, it restores the copper the new lead needs, so knowing prep includes repair widens what you can save (9.3). It matters because leveling is the make-or-break for fine-pitch and BGA: a part with dozens of leads or hidden balls seats evenly only on coplanar pads, so solder leveling is often the difference between a clean install and a board full of bridges and opens. It matters because conformal coating and obstructions silently defeat soldering: solder will not wet through coating, and heating it makes fumes, so clearing it is a step you cannot skip on a coated board. And it matters because the readiness check prevents wasted installs: committing a new part to an unprepared site means desoldering it right back off, so verifying the site is ready first saves the part and the work (9.5). Prepare the site well, and the installation that follows has every chance to succeed.
Required Prerequisites
- Pad Condition Assessment After Removal — Section 9.3 assessed and graded the site; this section prepares it. You should know what a good site looks like and what defects you graded (9.3), how to wick solder and clean flux (6.6; Chapter 3), that low-melt residue must be removed (9.2; alloy compatibility), and how overheating lifts a pad (5.4).
Recommended Consumables
- Solder wick and flux (Chapter 3) — to strip old solder and level the pads
- Fresh solder — for re-tinning and leveling the pads
- Isopropyl alcohol and a brush — to clean off all flux and, critically, low-melt-alloy residue (9.2)
- Fine copper wire or a pad-repair kit — for jumpering or replacing a torn-off pad (as needed, 9.3)
- A conformal-coating remover or a scraper/pen — if the board is coated
- Eye protection and ventilation — hot work, flux fume, and any conformal-coating fumes (Chapter 3)
Recommended Practice Hardware
- A temperature-controlled iron with a wicking-friendly tip (Chapter 4) — for stripping and leveling
- A magnifier or microscope and good light (Volume 2, Chapter 9) — to check the pads are flat, clean, and coplanar
- Removed/scrap sites — some with residue, lifted pads, or coating — to practice each prep step
- A hot air station (8.1) — helpful for leveling and for coated-board work
- A board holder and an ESD-safe surface
Real-World Applications
Preparing the site is a step every replacement passes through, and doing it well is what makes the new part go on cleanly. A technician who removed an SOIC with a low-melt alloy strips the pads, then cleans them specifically with alcohol until no bismuth residue remains, before doing anything else (alloy compatibility). A repairer who found a lifted pad in assessment re-bonds and tacks it down as part of prep, restoring the copper before the new part goes near it (pad repair; 9.3). Someone preparing a fine-pitch QFP site wicks and levels every pad flat and coplanar, knowing an uneven pad would leave one lead high (open) and pinch its neighbor (bridge) (solder leveling; coplanarity). A repairer working a conformally-coated board removes the coating from the pads and the surrounding area, and ventilates, because solder will not wet through it and heating it makes fumes (conformal coating). And a builder who once installed a part onto an unprepped, residue-laden site and had it fail now always finishes prep with a readiness check against the good-site standard (9.3). The failures site prep prevents: a brittle joint from bismuth residue, a part installed onto a missing pad, bridges and opens from uneven pads, and solder that will not wet through coating — all cleared before the new part is committed.
Common Challenges
- Invisible low-melt residue. Bismuth left on a clean-looking pad makes a brittle joint — after a low-melt removal, clean the pads specifically with alcohol until bright (alloy compatibility).
- Pads at different heights. An uneven site makes a fine-pitch or BGA part sit crooked, causing bridges and opens — wick and reflow every pad flat and coplanar (solder leveling).
- Solder won't wet the pad. Conformal coating or contamination is in the way — remove the coating and clean the pad to bright copper before tinning (conformal coating).
Safety Notes
Risk Level: Medium. Site prep is hot work with an iron and wick, and coated boards add a fume hazard — the goal is a ready site, reached without lifting a pad or breathing coating fumes.
Professional Tips Before Starting
- Strip, then hunt the residue. Wick the pads flat, then specifically clean off flux and any low-melt-alloy residue with alcohol until the copper is bright — the invisible bismuth is the residue that ruins the next joint (alloy compatibility).
- Level for the part you are fitting. A two-lead chip is forgiving, but a fine-pitch QFP or a BGA demands flat, coplanar pads — solder-level the site to the precision the package needs (coplanarity).
- Clear the coating before you heat. On a conformally-coated board, remove the coating from the work area and ventilate first — don't try to solder through it (conformal coating).
Getting the Site Ready for a New Part
What Site Prep Achieves
Site preparation has one job: to turn the assessed site into a surface that a new part can seat on and solder to correctly. Assessment (9.3) told you the condition of the site and what, if anything, was wrong; preparation is where you act on that — cleaning, repairing, and leveling until the site matches the good-site standard you learned to recognize. The finished, prepared site has four qualities: it is clean (no old solder blobs, no flux, and crucially no low-melt-alloy residue), it is flat and coplanar (every pad the same, even height), it is intact (any lifted or torn pad repaired), and it is ready (fresh flux, and paste if needed, for the install to come). Everything in this section is a step toward those four qualities. The order matters: you strip the site clean first, then repair any damaged pads, then level the pads even, then clear any coating, and finally flux for the new part — because you cannot level a pad you have not stripped, or trust a pad you have not repaired. Think of prep as building the foundation: the new joint you make in the next section (9.5) is only ever as good as the site you prepare for it here, so prep is not a formality between removal and installation — it is what makes the installation succeed.
Stripping the Site — Solder and Residue
The first step is to strip the pads back to a clean, bare, or lightly-tinned surface, removing everything the old part and its removal left behind. Start with the old solder: the pads are coated in the melted remains of the old joints — blobs, ridges, uneven lumps — and you wick it all away with solder wick and flux until the pads are flat and even, either bright bare copper or a thin, smooth tinning (6.6). Then clean the flux residue: the rosin or no-clean residue left from removal and wicking should be washed off with isopropyl alcohol so it does not interfere and so you can see the pad. And then, most important, hunt the invisible contaminant: if you removed the part with a low-melting-point alloy (tin-bismuth), some of that bismuth-bearing alloy is mixed into the solder on the pads, and it will make the next joint weak and brittle (alloy compatibility, 9.2). A pad can look bright and clean and still carry it, so after any low-melt removal you must wick and clean the pads specifically to remove every trace of the alloy — this is the single most important part of stripping the site. When you are done, the pads are clean, bright, flat, and free of old solder, flux, and above all any low-melt residue: a blank slate for the repairs and leveling that follow.
Pad Repair — Lifted and Torn Pads
If the assessment flagged a lifted or torn pad, preparation is when you repair it — restoring the copper the new part's lead needs to land on. Pad repair is the set of techniques for restoring a damaged pad, and the approach depends on how bad the damage is (9.3). A pad that is only partly lifted — loosened or raised at an edge but still present — is often re-bondable: you gently re-seat it flat and tack it back down, sometimes with a dab of adhesive, restoring it to a usable land. A pad that is torn off entirely — gone, with no copper left — needs more: you either install a replacement pad (a small pre-made copper pad bonded in place) or run a jumper wire from where the new part's lead will sit to the trace that pad connected to, re-establishing the electrical path. These are established repair procedures — the formal standards (IPC-7711/7721) define them in detail, and pad repair is a skill worth learning in its own right — so treat this as the overview: the point is that a damaged pad is not necessarily the end of the repair, and fixing it is part of preparing the site. A repaired pad gives the new lead something to land on and connect through, so you do the repair now, before leveling and installing: the site is not ready while a pad the new part needs is still lifted or gone.
Re-Tinning and Leveling the Pads
With the site stripped and repaired, you make sure the pads are the right height and even — a thin, flat, coplanar surface — because how level the pads are decides how well the new part seats. For a simple part, leaving the pads as bright bare copper or a thin, even tinning is enough. But for fine-pitch and especially BGA sites, evenness becomes critical, and the technique is solder leveling: you wick and reflow the residual solder on the pads so that every pad ends up flat and at the same height — the same coplanar surface across the whole footprint (coplanarity). Here is why it matters: a part with many leads or a grid of balls can only seat evenly on pads that are all the same height. If some pads sit high and others low, the part lands crooked — a lead over a high pad is pressed down and can bridge to its neighbor, while a lead over a low pad is held up off the solder and makes an open. On a coarse two-lead part this is forgiving, but on a fifty-lead QFP or a ball-grid array, uneven pad heights are a direct route to a board full of bridges and opens. So you level the pads to the precision the package demands: wick each one flat, reflow to an even, minimal, coplanar coat, and check under magnification that no pad stands proud or sits low. Leveling is the quiet step that separates a clean fine-pitch install from a frustrating one: even pads let the part seat true, and a part that seats true solders cleanly.
Conformal Coating and Other Obstructions
Some boards carry a protective coating or other material over the site that must be cleared before you can solder, and missing it defeats the whole install. Many boards — especially those built for harsh or humid environments — are covered with conformal coating*, a thin protective film over the components and the board*. It has two consequences for your work: solder will not wet through it, so a pad still under coating cannot make a joint, and heating or burning the coating gives off harmful fumes. So on a coated board you must remove the coating from the pads and the surrounding work area before soldering — with a coating-removal solvent, a scraper, or a coating-removal pen — and ventilate well; you never simply solder over or through it. Beyond coating, clear any other obstruction from the site: old adhesive that held a part down, potting compound, or debris — all of which can block a pad or a part from seating. The principle is that the site must be physically clear for the new part and for the solder to reach the copper: anything between the pad and the joint — coating, glue, grime — has to go first. Clear the coating and obstructions, ventilate the fumes, and you have a site the solder can actually reach: a coated or cluttered site is not a ready site, no matter how clean the pads beneath look.
Final Prep and Readiness
The last step is to flux the site for the new part and confirm, deliberately, that it is truly ready — because the whole point of prep was to reach that readiness. Apply fresh flux to the pads (Chapter 3), and if the installation will use solder paste (as many hot-air placements do), apply the paste now (8.5) — the solder source and flux the new part needs to reflow cleanly. Then do a final, deliberate readiness inspection, checking the site against everything prep was meant to achieve: are the pads clean and bright, free of old solder, flux, and any low-melt residue? are they flat and coplanar? is every lifted or torn pad repaired? is all coating and obstruction cleared? is the fresh flux (or paste) in place? Only when the answer to all of these is yes — when the site matches the good-site standard you assessed against (9.3) — is it ready for a new part. This readiness check is the gate: it is far cheaper to catch an un-cleaned pad or an unrepaired site now than to install a part, watch it fail, and desolder it back off (9.5). So finish every site prep the same way: flux it, inspect it against the standard, and only commit a new part when you have confirmed the site is ready — strip, repair, level, de-coat, flux, and verify, in that order, and the foundation for the new joint is sound.
Common Mistakes
- Leaving low-melt residue on the pads. Invisible bismuth makes the new joint brittle — clean specifically with alcohol after a low-melt removal until the copper is bright (alloy compatibility).
- Installing without repairing a lifted or torn pad. The lead has no copper to land on — do the pad repair as part of prep (9.3).
- Skipping leveling on a fine-pitch or BGA site. Uneven pads make the part sit crooked and cause bridges and opens — solder-level to a flat, coplanar surface (coplanarity).
- Soldering over conformal coating. Solder won't wet through it and it makes fumes — remove the coating and ventilate first (conformal coating).
- Skipping the readiness check. An unprepared site gives a failing joint — verify clean, flat, coplanar, repaired, and fluxed before installing (9.5).
Troubleshooting Guidance
Site-prep problems trace to incomplete stripping, un-repaired damage, uneven pads, or coating. If the new joint is brittle: low-melt-alloy residue was left on the pads — strip and clean specifically for bismuth (alloy compatibility). If a lead has nowhere to land: a torn pad was not repaired — jumper or replace it before installing (pad repair; 9.3). If a fine-pitch part bridges and opens: the pads were not coplanar — wick and level every pad flat and even (solder leveling). If solder won't wet a pad: conformal coating or contamination is on it — remove the coating and clean to bright copper (conformal coating). If you lifted a pad while prepping: you overheated it wicking or leveling — use flux, adequate tip heat, and short passes, not dwell (5.4). If the site looks clean but the install fails: you skipped the readiness check — verify against the good-site standard before committing a part (9.3). If old adhesive keeps a part from seating: an obstruction is on the site — clear it before installing. The throughline: strip everything off, repair every damaged pad, level the pads coplanar, clear any coating, then flux and verify ready.
Verification & Testing Methods
Use this as a site-prep check:
- [ ] I strip the pads of all old solder with wick, clean off all flux, and — after a low-melt removal — remove every trace of the bismuth-alloy residue (alloy compatibility).
- [ ] I repair any lifted or torn pad the assessment flagged, re-bonding a lifted pad or jumpering/replacing a gone one (pad repair; 9.3).
- [ ] I re-tin and, for fine-pitch or BGA sites, solder-level the pads so every one is flat and coplanar (coplanarity), understanding uneven pads cause bridges and opens.
- [ ] I remove any conformal coating and obstructions from the work area, and ventilate, because solder won't wet through coating and it gives off fumes.
- [ ] I apply fresh flux (and paste if the install uses it) to the ready pads (8.5).
- [ ] I do a final readiness check that the site is clean, flat, coplanar, repaired, and fluxed before committing a new part (9.3; 9.5).
Then try the practice exercises below — site-prep practice; scenarios differ from the quiz.
Practice Exercises
- Strip a site clean (8 minutes, applied). On a removed site, wick off all old solder to flat pads, clean the flux, and — if it was a low-melt removal — clean specifically until no residue remains, then inspect that the pads are bright (alloy compatibility).
- Level a fine-pitch site (10 minutes, applied). On a QFP or fine-pitch site, wick and reflow every pad to a flat, even, coplanar coat, checking under magnification that none stands proud or low (solder leveling; coplanarity).
- Clear a coated site (6 minutes, applied). On a conformally-coated scrap board, remove the coating from the work area with a remover or scraper, ventilating, and clean the pads to bright copper (conformal coating).
- Run the readiness check (5 minutes, inspection). After prepping a site, inspect it against the good-site standard — clean, flat, coplanar, repaired, fluxed — and decide whether it is truly ready for a part (9.3).
These core ideas — what prep achieves, stripping the site, pad repair, re-tinning and solder leveling, clearing coating, and the readiness check — are tested in the Chapter Quiz at the end of this chapter, where a score of 80% is required to continue.
Key Takeaways
- Site preparation turns the assessed site into a clean, flat, coplanar, repaired, and fluxed surface a new part can seat and solder on — assessment found the problems (9.3), prep fixes them, before any part goes on.
- Strip the pads: wick off all old solder to flat pads or bright copper, clean the flux, and above all remove every trace of invisible low-melting-point alloy residue, which makes the next joint brittle (alloy compatibility, 9.2).
- Pad repair restores a damaged pad: re-bond a partly-lifted pad, or replace or jumper a torn-off one to its trace — giving the new lead copper to land on (a defined IPC-7711/7721 skill, 9.3).
- Solder leveling makes every pad flat and the same height (coplanarity) — essential on fine-pitch and BGA sites, because uneven pads make the part sit crooked and solder into bridges and opens.
- Clear any conformal coating and obstructions from the work area (solder won't wet through coating, and heating it makes fumes), then apply fresh flux or paste (8.5) and verify the site is clean, flat, coplanar, and repaired before installing (9.5).
Skills Learned
- You can now explain what site prep achieves before a new part goes on.
- You can now strip the pads clean of old solder, flux, and low-melt residue.
- You can now describe pad repair for a lifted or torn pad.
- You can now re-tin and solder-level the pads to a flat, coplanar surface.
- You can now clear conformal coating and verify the site is ready.
Glossary Additions
- pad repair — the set of techniques for restoring a printed circuit board pad that has been lifted or torn off during rework, so a component lead can again land and connect there; a partly-lifted pad is re-seated flat and re-bonded (sometimes with adhesive), while a pad torn off entirely is replaced with a pre-made copper pad or bypassed with a jumper wire run from the lead's position to the trace the pad connected to. Pad repair is a formally standardized skill (IPC-7711/7721) and is part of preparing a damaged site for a replacement part.
- solder leveling — the step of wicking and reflowing the residual solder on a set of pads so that every pad is left flat and at the same height — a thin, even, coplanar surface across the whole footprint — before a new part is placed; solder leveling is especially important for fine-pitch and area-array (BGA) sites, because a part with many leads or hidden balls can only seat evenly on coplanar pads, and uneven pad heights make the part sit crooked and solder into bridges and opens.
Suggested Next Sections
Must read next:
- Installing a Replacement IC — with the site stripped, repaired, leveled, and fluxed, the next section is the install itself — placing the new part aligned to its footprint and pin 1, and soldering it in by iron or hot air so every joint is sound.
Recommended:
- Pad Condition Assessment After Removal — the assessment that tells you what this preparation must fix.
- Component Placement with Hot Air — how a part is placed and reflowed onto the prepared, fluxed, or pasted pads.