A board comes back from the line with one lifted pad and one wrong resistor. The resistor swap is routine. The pad is a different category of work, with different approval, different limits and a different paper trail. Assembly houses that treat both as "fix it and move on" produce boards that work and cannot be defended a year later when a customer asks what happened to serial 2141.
Two standards draw the line: IPC-7711 for rework and IPC-7721 for repair and modification. Here is what the split means in a purchase order, what the limits look like, and what a record has to contain.
Rework, repair and modification are not the same thing
| Operation | Definition | Examples | Approval |
|---|---|---|---|
| Rework | Restoring a part or joint to the drawing and the workmanship standard | Replacing a component, resoldering a joint, reballing a BGA, removing excess solder | Covered by the build package under IPC-7711 |
| Repair | Restoring function where the board no longer matches the drawing | Lifted pad replacement, conductor repair, laminate repair, jumper wire | Requires customer approval, per IPC-7721 |
| Modification | Changing the assembly from the released drawing on purpose | Adding a wire for an engineering change, cutting a trace, adding a component | Requires a written change instruction and approval |
The distinction is not academic. Rework is expected, priced and inspected as part of normal production. Repair changes the hardware, so it has to be approved before it happens, recorded against the serial number, and inspected to the same class as the rest of the lot. Modification without a released change instruction is a nonconforming product no matter how well it works.
What the two standards actually cover
IPC-7711 covers the rework processes: component removal and replacement for through-hole and surface mount parts, solder joint rework, BGA and CSP reballing, lead trimming and forming where the drawing allows it, and the tooling and thermal conditions for each. It is organised by operation, so each procedure states the equipment, the temperature window, the inspection criteria and the precautions.
IPC-7721 covers repair and modification: replacing a damaged pad or land, repairing a broken conductor with a wire, repairing laminate damage such as a burned or delaminated area, adding a jumper for an approved change, and cutting a trace. Each of these operations alters the board, so the standard requires that the work be signed off, performed to a documented procedure, and inspected.
The limits that have to be written down
| Item | Typical rule | Why it matters |
|---|---|---|
| Rework cycles per joint | Three, or the component supplier limit if lower | Each thermal cycle degrades the pad, the mask and the intermetallic layer |
| Lifted pad replacement | Repair, approval required, class dependent | A replaced pad carries less peel strength than the original |
| Jumper wires | Repair, approved, length and routing controlled | A free wire can short or break in vibration if it is not staked |
| Conformal coating after rework | Recoat the opened area | An uncoated rework window becomes the first corrosion site |
| Reballing a BGA | Rework, with X-ray verification | Missing or bridged balls pass a functional test and fail in the field |
| Mixed alloys | Not allowed without approval | Lead-free and tin-lead residue on the same joint reduces reliability |
Three cycles is a ceiling rather than a target. A joint that needs a fourth pass is usually a process problem, and the honest answer at that point is scrap the assembly and fix the cause.
Where rework goes wrong
- Heat without a profile. A hot air handpiece set by feel overheats the part and the neighbours. Rework stations with a controlled profile and a thermocouple on the joint behave the same way every time.
- No bake before the second pass. A moisture sensitive package that sat on a bench gets popped or delaminated when it is reheated. Floor life applies to rework exactly as it applies to first build.
- Solder mask damage. A lifted mask edge next to a reworked pad traps flux and opens a path for dendritic growth later.
- Flux left behind. Rework flux is often more active than the production paste. If it is not cleaned, residue stays under the part where no inspection sees it.
- Charged parts and charged boards. Rework benches sit outside the main line more often than anyone admits, and a board handled there without a wrist strap gets the same latent damage as anywhere else.
- No record. The most common finding is not a bad joint, it is an undocumented one.
What the record has to show
One line per operation is enough if it carries the right fields: serial number or lot, component reference, operation performed, standard applied with class, operator, date, material and paste lot, rework cycle count, inspection result and the inspector. For a repair, add the approval reference. For a reball, add the X-ray image reference. That record is what turns a reworked board into a documented product instead of a favour.
How SUPERB Assembly handles rework
SUPERB Assembly works to IPC-7711 for rework and IPC-7721 for repair and modification, with the class of work set by the drawing: IPC-A-610 Class 2 or Class 3 against J-STD-001. Rework is done at controlled stations inside the ESD protected area, with profile controlled hot air and infrared tooling, and reballed BGAs are verified on a CT capable X-ray before release. Moisture sensitive parts go back through a 125 C bake to J-STD-033 before the second pass.
Every reworked assembly carries a record against its serial number, and repairs are quoted and approved before the work starts rather than reported afterwards. Incoming material is counted on an X-ray counter, bare boards are checked against IPC-6012, and finished lots are inspected with 3D AOI, X-ray and ICT or FCT as the drawing requires.
- IPC Class 2 and Class 3: how the workmanship class changes the acceptance of a reworked joint.
- AOI and X-ray: what each method can see after a rework operation, and what it cannot.
- PCBA workshop: the stations, tooling and inspection equipment behind the record.
Frequently asked questions
Does a reworked board still meet Class 3?
Yes, if the rework was performed to IPC-7711 and inspected to the Class 3 criteria, including pad and mask condition around the joint. What fails Class 3 is the damage around the work, not the fact that the work happened.
Can a lifted pad be replaced on a fine pitch part?
Sometimes. It depends on the pad size, the trace width and the space around it, and it is a repair that needs approval. On a 0.4 mm pitch device the repair is often less reliable than replacing the assembly, and the honest answer is to say so before the work starts.
Who decides whether a board is reworked or scrapped?
The build package decides what rework is allowed. Repair and modification need the customer, because they change the hardware from the released drawing. A supplier that decides this alone is making a product decision that belongs to the buyer.
Next step
Send the assembly drawing with the workmanship class, the approved rework and repair rules you want applied, and the rework record format your quality group needs. The reply confirms the stations, the inspection after rework, and what ships with each reworked serial.
