Quick answer
Mixed-technology PCBA planning is the work of freezing one executable route for surface-mount and through-hole content. Classify every part, decide the SMT side sequence, choose wave, selective, pin-in-paste or controlled hand soldering only after access and component limits are known, then define inspection, electrical test and release records. The route must be tied to one BOM, placement set, drawing revision and change-control baseline—not inferred on the production floor.
A mixed-technology assembly is not finished planning when the BOM contains both SMT and through-hole parts. The build still needs one executable sequence for board sides, paste, placement, reflow, insertion, wave or selective soldering, controlled hand operations, inspection, programming and electrical or functional test. If those decisions are left implicit, the first production build becomes the process-design meeting.
PCBArise publishes PCB assembly routes that can coordinate SMT, THT, sourcing, inspection and project-specific testing. The exact sequence and coverage are confirmed from the released BOM, centroid data, drawings, component limits, board geometry, quantity, tooling and acceptance needs. The route below is a decision framework, not a claim that every listed operation applies to every order.
What is mixed-technology PCBA planning?
Mixed-technology planning converts a component mix into a revision-controlled route. It identifies which parts are placed on each side, which parts can tolerate the scheduled thermal exposures, which THT joints have wave or selective access, which odd-form operations need a work instruction, and what evidence releases the assembly. The output is an approved baseline that production can execute and quality can audit.
This page owns process sequencing. If your first decision is whether a component should be SMT or THT, use the SMT vs through-hole comparison. If the THT footprint and mechanical interface are not yet closed, use the through-hole design checklist. Keeping those intents separate prevents one long article from obscuring the route decision.
Freeze the source package before choosing equipment
Begin with one assembly part number, revision, active variant and build stage. Reconcile the BOM, centroid or Pick & Place data, fabrication package and assembly drawings. Mark fitted and DNP positions, polarity, insertion side, odd-form components, customer-supplied materials, programming needs and any component-specific handling or temperature limit.
Classify each operation rather than only each package: SMT top, SMT bottom, pin-in-paste candidate, conventional THT insertion, press-fit, connector or cable operation, hand-solder exception, programming, coating or final integration where applicable. This exposes conflicts such as a tall connector blocking a later stencil or pallet, a bottom-side package entering the wave envelope, or a heat-sensitive part scheduled too early.
Choose the through-hole branch from the actual board
Wave soldering can support a suitable solder-side population and repeat batch route, but orientation, shadowing, underside package exposure, masking or pallets and component compatibility must be reviewed. Selective soldering localizes the operation, yet nozzle path, keepout, preheat, flux access, board support and thermal mass still determine feasibility.
Pin-in-paste, also called intrusive reflow, can place compatible THT joints into a reflow route when the component is qualified for the exposure and the stencil, paste volume, lead protrusion, hole geometry and acceptance result are validated. Controlled hand soldering may remain appropriate for a low-count odd-form or inaccessible special joint, but it requires defined access, tools, workmanship and repeatability rather than an undocumented exception.
| Planning layer | Questions to close | Primary inputs | Release output |
|---|---|---|---|
| Configuration | Which revision and variant is being built? | BOM, file manifest, drawings | One controlled release identity |
| SMT sides | Which side runs first, and what sees each reflow? | Centroid, package data, stencil and board support | Approved print/place/reflow sequence |
| THT branch | Which joints use wave, selective, pin-in-paste or hand? | Hole/lead fit, solder-side access, component limits | Route, tooling and work instructions |
| Inspection | Which visible and hidden risks need evidence? | Package geometry, workmanship criteria, defect risks | Inspection method and records |
| Electrical release | Which connectivity or functions must be exercised? | Test access, firmware, limits and fixtures | Approved program and result format |
| Change control | Which changes reopen qualification? | Revision, alternate, tooling, process and test rules | Named review and approval path |
Sequence the SMT sides before THT insertion
A common planning tendency is to complete required SMT reflow before inserting tall or obstructive THT parts, but that is not a universal recipe. Double-sided SMT introduces board-support, component-mass and second-reflow questions. Bottom-side parts that could see a later wave need explicit component compatibility, orientation and protection decisions. A connector qualified only for a specified process must not inherit another package's thermal guidance.
Texas Instruments' wave-exposure report shows why moisture, time, temperature and PCB design must be considered when SMT packages enter a wave-solder environment. It is an application study, not a generic authorization for every package or profile. Use the current component datasheet and manufacturer note, then validate the selected board-level route.
Plan access, tooling and thermal mass together
A selective nozzle or wave pallet needs physical space and stable support. Review nearby component bodies, solder joints, board edges, tooling holes, conveyors, clamps, fiducials and any region that must be masked. Large copper areas, thick boards, shields, terminals and transformers can change heat flow and process development. Thermal relief is an electrical and assembly decision; do not apply it without considering current, thermal and mechanical requirements.
Panelization and breakaway features also affect handling and access. Confirm whether the board remains panelized through all solder and inspection operations, how tall or heavy parts are supported, and when depanelization occurs. If an operation occurs after depanelization, its fixture and strain risks belong in the route.
Map inspection and test to each branch
SPI and AOI can support the SMT print and visible placement/reflow questions they are configured to inspect. Visual inspection can cover observable THT workmanship. X-ray may support defined hidden-joint or barrel questions. ICT, flying probe and functional test cover different accessible electrical or behavioral requirements. None is a universal substitute for the others.
The PCB assembly testing page and electrical-test comparison help define coverage. For each gate, name the inspected feature or exercised behavior, unit or lot scope, conditions, limits, result record and failure disposition. A passing result means the approved check passed under its stated conditions—not that all possible defects are absent.
IPC J-STD-001J assigns the user responsibility for product class and provides soldered-assembly process and acceptance context. IPC-A-610J addresses post-assembly acceptability and is often used with it. The project must identify the applicable revision and criteria. PCBArise's quality-control route does not replace customer or product-owner responsibility for final product requirements.
Mixed-technology release flow
The pilot must prove the unresolved route decisions. Record paste and placement findings, thermal or support issues, insertion and solder observations, visible and hidden inspection results, test outcomes and disposition against the exact baseline. If the result requires rework, separate a one-time pilot correction from the repeat-production process and update the controlled documents.
Printable mixed-technology PCBA release checklist
Configuration and materials
- □ Assembly part number, revision, variant, build stage and file manifest agree.
- □ BOM, centroid, assembly drawing and fitted/DNP population reconcile.
- □ Exact component MPNs, approved alternates, packaging and special handling are controlled.
- □ Component temperature, moisture, insertion, press-fit or mechanical limits are available where needed.
Process route
- □ SMT top/bottom print, placement, reflow and support sequence is defined.
- □ Every THT joint has an approved wave, selective, pin-in-paste or controlled hand branch.
- □ Pallet, nozzle, masking, tooling, conveyor, support and rework access are reviewed.
- □ Tall and heavy components, copper mass, panelization and depanelization are included.
Evidence and release
- □ Workmanship class, applicable revision and project acceptance criteria are identified.
- □ SMT, visible THT, hidden-joint, electrical and functional risks map to defined evidence.
- □ Pilot results, failure disposition, repair and retained records are tied to the released route.
- □ Alternate, layout, stencil, pallet, profile, firmware, fixture, test or acceptance changes trigger review.
Print this page or save it as PDF for the NPI route-freeze meeting. The checklist supports review; the released files, quotation, work instructions and acceptance documents remain authoritative.
Bring one mixed-technology package to review
Provide the controlled fabrication data, BOM, centroid, drawings, component constraints, quantity and build stage, along with inspection, programming and test needs. PCBArise can then evaluate the THT branch, SMT route and evidence as one assembly plan. Use the project review page when the package is ready.
Engineering review
Prepared and reviewed for project use
Engineering Director
Senior Quality Engineer
Review scope: technical accuracy, evidence wording, standards references, internal links and release readiness. Project requirements remain subject to the released files, applicable acceptance criteria and agreed test documentation.
FAQ
Questions engineers ask before release
What is a mixed-technology PCBA?+
It is an assembled printed circuit board that uses both surface-mount and through-hole or other leaded operations. Planning must define the board-side sequence, solder branches, tooling, inspection and test against one controlled revision.
Should SMT always be completed before through-hole insertion?+
It is a common route when tall THT parts would obstruct printing, placement or reflow, but it is not universal. Pin-in-paste, bottom-side exposure, press-fit parts and component-specific limits can change the sequence. Confirm the actual board and package data.
How do I choose wave or selective soldering for a mixed board?+
Review solder-side population, component compatibility, orientation, shadowing, pallet or nozzle access, board support, copper mass, quantity and evidence needs. The suitable branch is a board-specific engineering decision, not a simple component-count threshold.
When can pin-in-paste be used for through-hole components?+
Consider it only when the exact component is qualified for the reflow exposure and the footprint, hole, stencil, paste volume, protrusion, thermal profile and acceptance result can be validated for the assembly.
What inspection is needed for mixed-technology PCBA?+
Map methods to the risks and access. SPI and AOI may support SMT process questions, visual inspection covers observable THT workmanship, X-ray can address selected hidden features, and electrical or functional tests verify only their defined scope.
What changes require the mixed assembly route to be reviewed again?+
Review the affected gates after a component alternate, footprint or layout change, stencil or panel change, solder branch, pallet or profile change, firmware or fixture change, test update or new acceptance requirement.
Reference points
Sources and verification starting points
External standards and industry references help frame the decision. Confirm current supplier evidence and project-specific requirements before release.
- Global Electronics Association — IPC J-STD-001J assembly scope and classification responsibility
- Global Electronics Association — relationship between solder-process and post-assembly acceptance standards
- Texas Instruments — Wave Solder Exposure of SMT Packages application report
- Texas Instruments — package-specific assembly guidance index