Volume 4
Pcb Theory Construction And Repair
9 chapters · 46 sections · 973 minutes of reading.
0/46Before you can repair a board you have to understand what a board is — and this opening chapter builds that foundation from the ground up. It starts with what a printed circuit board actually is and why it replaced hand-wiring, then works through how boards are constructed: single, double, and multi-layer builds, the layer stackups that organize the copper, the FR4, Rogers, and flexible materials boards are made from, and how copper weight sets how much current a trace can carry. By the end you can look at a bare board and read its physical structure — the substrate, the copper, the layers — which is the knowledge every trace, pad, and via repair in this volume depends on.
Chapter 1 built the board from the outside in; this chapter zooms into the three features you actually repair. It examines the trace that carries a signal or power from one point to another, the via that passes a connection through the board between layers, and the pad where a component solders down — their anatomy, the different types and geometries each comes in, how much current and how fast a signal they can carry, and, crucially for repair, how to read and follow them on real, dense, multi-layer boards. By the end you can look at any board and read its traces, vias, and pads for what they are and where they go.
Chapter 2 read the board's copper as features you can see and follow; this chapter turns to how fast signals actually behave on that copper. It explains controlled impedance — why some traces must be built to a precise width over a reference plane — the ground and power planes that carry a signal's return current and steady the board, the copper pours and fills that blanket the empty spaces, and how these choices cut EMI and hold a signal's integrity. It closes by showing how to recognize the impedance-controlled traces and layers you must treat with special care. By the end you can look at a board and tell which traces are ordinary and which are engineered for speed — and why that difference matters the moment you repair them.
Chapter 3 finished the board's electrical story; this chapter turns to how a bare board is actually made and the defects that manufacturing can leave behind. It walks the fabrication steps — laminating the layers, drilling and plating the holes, patterning and etching the copper, and applying the solder mask, surface finish, and silkscreen — then catalogues the flaws those steps can produce: etching and plating faults, delamination, and manufacturing-induced cold joints and bridges. It closes by showing how to assess whether a board is worth repairing at all. By the end you can tell a manufacturing defect from field damage, know where each kind of flaw comes from, and judge a board's repairability before you begin.
The diagnostic half of the volume is done and the board in front of you has been judged worth repairing; this chapter picks up the iron and repairs the first thing that fails on a damaged board — a broken copper trace. It begins with the diagnostic skill of finding and characterizing a damaged trace, then works through the repair methods in order of the damage they suit: conductive ink for the lightest breaks, a solder bridge for a short gap, and magnet wire for a longer run or a cleaner rebuild. It draws the line between a surface trace you can reach and an inner-layer trace you cannot, and closes by showing how to verify that a repaired trace is electrically sound and mechanically secure. By the end you can locate a break, choose the right repair for it, carry that repair out safely with a hot iron, and prove it holds.
With traces repaired, this chapter turns to the other copper feature a repair most often has to save: the pad — the copper landing a component leg, wire, or ball solders to. Pads fail in their own ways: lifted from the board by heat or prying, torn away entirely, or damaged at the ring around a plated hole. The chapter works through them in order of severity — re-adhering and reconnecting a pad that has lifted but survived, rebuilding a pad that has been destroyed, repairing the annular ring of a through-hole pad, and the exacting work of restoring a fine-pitch or BGA pad — then closes by verifying that a repaired pad is electrically sound and mechanically able to hold a component. By the end you can assess pad damage, choose the right repair for it, carry it out with a hot iron and the right materials, and prove the pad will hold.
Traces carry a signal across a layer and pads land a component; vias carry a connection between layers, through the plated hole that ties a board's copper together in the third dimension. This chapter repairs them. It begins by identifying a failed via — a cracked or corroded barrel, a broken layer-to-layer connection, an intermittent joint that opens under flex or heat — and telling a repairable surface via from a buried one that is not. It then works through the repair methods: restoring the through-connection with a rivet or eyelet set in the hole, and rejoining the layers with a wire through the hole or a conductive fill. It closes by verifying that a repaired via truly carries its connection from layer to layer and holds under service. By the end you can find a failed via, judge whether it can be repaired by hand, restore its connection by the right method, and prove the repair sound.
Traces, pads, and vias restore a board's original wiring; jumper wires go further — they carry a connection along a new path of their own, whether to bridge damage nothing else can reach, to reroute around a ruined area, or to add and change connections a board never had. This chapter treats the jumper wire as a repair tool in its own right. It begins with the fundamentals — what a jumper is, the wire to choose, and when a jumper is the right answer — then works through installing a clean point-to-point jumper, using bodge wires to modify or correct a board, and mounting components in free air by dead-bug and air-wire techniques. It closes by securing and verifying jumper wiring so it holds and conducts as reliably as the copper it stands in for. By the end you can choose, route, install, secure, and verify a jumper wire for repair or modification, and know when a wire is the best tool for the job.
Liquid is one of the most common ways a board is damaged and one of the most misunderstood — a spill, a leak, or condensation carries contamination into a board and, especially under power, sets corrosion working at its copper, joints, and components long after the board has dried. This chapter is the field guide to that damage: recognising it, arresting it, and repairing it. It opens by identifying liquid damage and corrosion — the tide lines, the green and white deposits, the eaten-away traces and pads, and what the type of liquid and the presence of power tell you about how far the damage has gone. It then works through cleaning a liquid-damaged board to stop corrosion at its source, repairing the traces and pads corrosion has eaten using the trace and pad techniques of the earlier chapters, and dealing with the corroded components and connectors that liquid attacks first. Because liquid damage rarely stops at what is visible, it covers post-liquid-damage diagnosis — hunting the secondary failures a spill leaves behind — and closes by verifying a corrosion repair so the board is not only fixed but proven clean, sound, and unlikely to corrode again. By the end you can assess a liquid-damaged board, clean and repair it, find the damage that hides, and return it to reliable service.