吃瓜tv 路 Joint-access workshop
Selective soldering starts with a reachable joint
Check nozzle access, lead geometry, flux, heat demand and fixture clearance. Build a practical through-hole soldering plan around the populated assembly.
Preliminary files and open process questions are welcome.
What is selective soldering used for?
Selective soldering brings a controlled solder contact to chosen through-hole joints instead of exposing the entire underside of the assembly to a broad wave. It is useful when connectors, transformers or other through-hole parts share a board with surface-mount components. The process combines local flux application, preheating, solder contact and inspection in an agreed sequence.
Its main design question is practical: can the selected nozzle reach every joint, deliver the required heat and leave without contacting or contaminating nearby features? A small solder opening alone does not answer that question. The nozzle body, positioning uncertainty, board distortion, fixtures and travel path all occupy space. A dense layout benefits from this review before the board is ordered.
The right route depends on the joint map and production requirement. Compare selective soldering with the complete through-hole assembly process, including hand and wave alternatives. An isolated joint, a long connector row and a high-thermal-mass power terminal may each require a different approach even on the same board.
Start from the joint centre and the nearest obstacle
For a simple local circular screen, measure from the target joint centre to the nearest obstacle boundary in the relevant working plane. Use the nozzle outside diameter, not its solder opening. Add the combined relative positioning allowance and the extra process clearance agreed with the equipment or process engineer. The result describes a local envelope, not a complete machine motion simulation.
An obstacle can be an SMD component, lead, test pin, fixture wall or an adjacent feature that must not contact solder. Its height matters. A low feature might conflict with the nozzle tip while a taller feature interferes with the wider nozzle body during approach. A top view without heights can therefore miss the most important restriction.
The equipment manufacturer shows that nozzle diameter, length and application differ. Its catalogue is not a list of 吃瓜tv's installed tooling. Obtain the actual nozzle drawing and process proposal for the project rather than copying an advertised minimum into the PCB design rules.
Check a local nozzle envelope before routing the path
Enter the nozzle outside diameter, combined worst-case relative positioning allowance, additional process margin and available centre-to-obstacle distance. Identify the drawing and measurement plane in the basis field. The worksheet keeps a negative margin visible so that a local conflict cannot disappear inside an average or a rounded 鈥減ass鈥� badge.
Selective Nozzle Clearance Screen
For an illustrative 6 mm outside diameter, 0.3 mm positioning allowance and 1 mm process margin, the required local distance is 4.3 mm. An available 5 mm gives 0.7 mm remaining clearance. That result says only that these entered dimensions do not overlap in the simplified view. It does not prove acceptable solder spread, thermal performance or machine accessibility.
Avoid counting uncertainty twice. If a fixture specification already includes board location error, document which additional errors remain to be added. If the nearest obstacle dimension is a worst-case minimum, do not also subtract the same tolerance inside the positioning allowance. Send the worksheet with a marked drawing; the numbers are much easier to review when their datums are visible.
A reachable joint must also be heatable
Heat demand depends on the lead, finished hole, barrel, copper connections and board construction. A large internal plane can remove heat from the joint even when access appears generous. Increasing solder contact time or temperature without understanding that path can expose adjacent materials to unnecessary stress. Review the actual copper geometry with the through-hole joint requirement.
Thermal reliefs can reduce local heat demand, but their electrical and mechanical suitability must be evaluated by the design team. High-current connections may need a different balance between solderability and conductor cross-section. Do not add reliefs automatically to every power terminal or remove them solely because a board carries high current.
Flux type, quantity and placement influence wetting and residue conditions. Preheat prepares the assembly and flux for solder contact; its appropriate settings depend on the chemistry and thermal mass. Use the flux supplier's instructions and a measured board profile. The wave soldering temperature guide explains why a bath setting, a board temperature and a component-body temperature must remain separate quantities.
Design the carrier and the board together
A fixture should locate and support the assembly while providing access to the intended joints. Include board thickness, expected distortion, component heights, panel rails and allowable contact regions. The fixture must also allow loading and unloading without force on fragile components. Review how the assembly sits when its heaviest through-hole parts are installed.
Windows can restrict flux delivery, solder access, observation or heat flow. A narrow opening that clears a pin in a drawing may be difficult to manufacture, clean or maintain in a durable pallet. Specify the functional requirement and let the process team confirm the opening and material. Repeated tooling contact should not damage mask, copper or component bodies.
Lead protrusion and clipping must be controlled as part of the route. Excess length can complicate access and withdrawal; a short lead may affect the agreed joint geometry. The appropriate limits depend on the assembly specification. Do not adopt a universal protrusion number without considering the component, finished board thickness and acceptance criteria.
Build a repeatable joint recipe and retain the evidence
The process record should identify the assembly revision, alloy, flux, nozzle, program and fixture. Record critical settings with their units and distinguish machine setpoints from measured results. A first-build trial is an opportunity to validate the joint map and to resolve restricted access before a production quantity repeats the same problem.
Review the approach and withdrawal path, not just the stationary position over the joint. Solder bridges, icicles or disturbed joints can involve withdrawal conditions, lead geometry, wetting or program order. Closely spaced joints may interact thermally. A route optimized only for minimum travel distance can miss the need for stabilization or the influence of neighboring work.
Nozzle condition also belongs in process control. The wettable surface, cleanliness and actual flow affect solder behavior; nominal diameter does not capture those changes. Record maintenance and replacement decisions that matter to repeatability. If the process is transferred to another machine or nozzle, review the equivalence rather than assuming identical programmed coordinates reproduce the same contact.
For comparison, the photograph below shows a broad wave-solder contact. Selective soldering targets local joints, while a broad wave treats a larger accessible underside. This picture explains the route difference; it is not presented as a selective-nozzle photograph or evidence of a particular installed machine.
Inspect workmanship and verify the product separately
Define the applicable workmanship criteria and revision before production. is the official starting point for selecting documents such as J-STD-001 and IPC-A-610. The contracted class, amendments and project-specific requirements still need agreement. Merely naming a standard does not establish certification or demonstrate compliance for a finished assembly.
| Review question | Evidence to request | What it does not prove alone |
|---|---|---|
| Did the intended joints receive solder? | Joint map and visual inspection | Electrical operation of the circuit |
| Is the through-hole joint acceptable? | Required views and applicable criteria | Reliability under every service condition |
| Were adjacent parts protected? | Access review and post-process inspection | Complete thermal qualification |
| Are residues acceptable? | Material compatibility and specified cleanliness controls | Suitability of every later coating |
| Does the assembly function? | Agreed electrical and functional test results | Hidden workmanship at untested locations |
Visual inspection, X-ray inspection and electrical tests answer different questions. Select them according to joint visibility and failure risk. If a hidden feature needs examination, specify the technique and required evidence. A photograph of a good external fillet is not a complete record of an inaccessible internal condition.
Link the findings to the first-piece inspection procedure and resolve deviations before repeating the build. Record whether a correction changes the board design, fixture, program, material or inspection plan. That distinction helps the next revision inherit a controlled process rather than an undocumented operator workaround.
Separate development from repeat assembly work
Selective soldering cost can include program preparation, nozzle selection, fixture development, profiling, cycle time, consumables and verification. Joint count alone is a weak pricing proxy: one restricted high-mass connector may require more development than many accessible pins. Provide the joint map and proposed volume so the quotation can reflect the actual route.
Selective Soldering Budget and RFQ Brief
The budget brief uses allowances you enter from a defined source. It contains no automatic market rate or assumed process yield. Leave all three cost fields blank to prepare a technical RFQ brief. If costs are entered, identify the source, date and scope, including whether components, PCB fabrication, other assembly work, freight and tax are included.
Changing quantity or technical scope clears the old allowances because they may no longer apply. For an arithmetic example, 20 acceptable assemblies at 18 currency units each, plus 150 setup and 90 batch verification, total 600. These illustrative values are not a 吃瓜tv quotation. Ask for a project review when access, materials or acceptance requirements are still unresolved.
Send a joint map that makes the review actionable
Include the current board and assembly drawings, BOM, through-hole component part numbers, quantity and intended build stage. Mark the joints proposed for selective soldering and the neighboring features that must remain untouched. Provide component heights, lead geometry, mechanical keep-outs and restrictions on which side can face the solder contact.
If a fixture already exists, supply its revision and relevant interface dimensions. If no fixture exists, state that tooling development belongs in the quotation. Identify the approved alloy and flux where fixed, the required inspection records and any cleaning or coating that follows. Preliminary data are welcome when unknowns are clearly identified.
Selective soldering design questions
Is selective soldering always cheaper than wave soldering?
No. Volume, joint distribution, access, tooling, cycle time and verification affect the result. Selective processing can avoid exposing nearby components to a broad wave, but its setup and sequential work must be included in the comparison. Compare the same acceptable quantity and inspection scope.
Can the nozzle fit if its opening is smaller than the gap?
Not necessarily. The outside body, required clearance and travel path matter. Provide the nozzle drawing and surrounding component heights. The worksheet intentionally starts with outside diameter and a local obstacle distance so the smaller solder opening cannot be mistaken for the full clearance envelope.
Can a high-copper board be selectively soldered?
Possibly, subject to thermal and process review. Copper connections can increase heat demand at the joint. Supply the stackup and local plane connections along with the through-hole geometry. A successful geometric clearance result does not answer the thermal question or establish a production recipe.
Does passing electrical test make visual inspection unnecessary?
No. Test coverage and workmanship evaluation are different parts of the release plan. A circuit can operate during a short test while still containing an unacceptable assembly condition. Define the required inspections and tests together, then retain the evidence associated with the delivered revision.
Request a selective soldering review
Send the drawing revision, BOM, quantity and the process question you need resolved. Include component instructions, mechanical restrictions and required inspection or test records where relevant.
Tool use is optional. Attach any downloaded brief manually; Contact does not automatically receive worksheet inputs. References reviewed September 2026. Illustrations are explanatory, and photographs are not process qualification records.