DFM / DFA review — joint class locked
IPC-A-610 Class 2 or Class 3 is fixed here, before panelisation and before the stencil is cut. Class decides inspection configuration, staffing and the traceability package.
MIXED-TECHNOLOGY · ONE WORK ORDER
One board, three processes, one work order.
Reflow, press-fit and hand soldering run as one sequence on 7 SMT and 2 THT lines at one Shenzhen site. The joint class is locked before the line is set and the stencil is cut.
PROCESS ORDER
Six steps, and the order is not negotiable
A mixed-technology board fails on sequence far more often than on machine capability. This is the order every mixed work order follows, and the control point that is signed off at each step.
Three inputs are enough for a first-pass route
Layer count, through-hole joint count and the acceptance class tell us whether selective, wave, press-fit or pin-in-paste is the right route — and the sequence it imposes.
SMT first pass
Paste print → 3D SPI → placement → reflow. The highest-temperature process runs first, so every joint made afterwards stays below the reflow profile already applied.
Second-side SMT
Double-sided assemblies go back through a carrier or fixturing that supports the populated first side. Board thickness runs 0.4–4.0 mm.
THT insertion
Axial and radial auto-insertion for high-volume passives, hand insertion for connectors, and press-fit for compliant-pin parts. Insertion force is set by the tooling, not by the operator.
Through-hole soldering
Selective soldering for localised heat, dual-wave with a pallet for high hole counts, hand soldering for connectors and rework. The choice is made per joint, not per board.
Inspection & test
AOI, X-ray to IPC-7095 void criteria, ICT or FCT, and an FAI record with SPI and AOI data. Inspection items are configured per project.
WHY THE ORDER IS WHAT IT IS
Highest temperature first, everything else second
Through-hole soldering happens after SMT reflow, so joints that are already made have to survive a second thermal cycle. That single constraint sets the sequence.
Reflow first, THT second
Reversed, the through-hole joints would be re-melted by the paste reflow profile. Running SMT first means the second excursion is the smaller of the two, and it is bounded by the J-STD-020 ceiling rather than by the solder alloy alone.
Selective soldering keeps the heat local
A single-point nozzle at 260–280 °C (lead-free, industry-typical) heats the joint in front of it and leaves neighbouring SMT parts alone. That is the reason mixed boards use selective rather than wave, not the positional accuracy.
Wave soldering heats the whole board
Lead-free wave runs 255–265 °C (industry-typical) across the full assembly, so the SMT side has to be masked by a pallet. Pallet tooling is USD 3,000–8,000 per design, and V-CUT depaneling then requires board thickness of at least 0.8 mm.
MSL exposure is re-checked before the second pass
Moisture-sensitive parts are re-counted against their floor-life budget before through-hole soldering. Parts that exceed the budget are baked before the second excursion; barrier bags, desiccant and humidity indicator cards follow the same flow as component sourcing.
PARAMETER WINDOW
The mixed-technology window in fifteen rows
Every row below is either a standard we work to, a machine parameter, or an industry-typical figure. The basis column says which.
| Parameter | Value | Basis |
|---|---|---|
| Work order scope | SMT reflow, press-fit and hand soldering inside one work order and one traceability record | Verified |
| Process order | SMT before THT — the highest-temperature process runs first | Standard practice |
| Joint class | IPC-A-610 Class 2 or Class 3, locked before panelisation and before the stencil is cut | IPC-A-610 |
| Through-hole fill | To IPC J-STD-001: Class 2 requires ≥75% barrel fill on the solder side; Class 3 requires 100% circumferential wetting plus ≥75% fill and a visible fillet | IPC J-STD-001 |
| Wave versus selective defect rate | Wave 500–2,000 PPM against selective 50–200 PPM on mixed assemblies | Industry-typical |
| Selective nozzle temperature | 260–280 °C lead-free, single-point localised heating | Industry-typical |
| Wave solder temperature | 255–265 °C lead-free, whole-board heating | Industry-typical |
| Second thermal cycle | Peak must stay below the 260 °C absolute ceiling of IPC/JEDEC J-STD-020 | J-STD-020 |
| Press-fit | Solderless compliant-pin insertion, insertion force controlled by the press tooling | Verified |
| Pin-in-paste | Requires 2–3× the normal paste volume, delivered by a stepped stencil or print-plus-dispense | Industry-typical |
| Board thickness | 0.4 – 4.0 mm for assembly | Line capability |
| Depaneling | V-CUT requires board thickness ≥0.8 mm; routing is the alternative; breakaway rail ≥5 mm | Panel rules |
| Tooling | Pallet or carrier USD 3,000–8,000 per design; selective-solder programming USD 500–1,000 | Industry-typical |
| Real cost of Class 3 | Assembly cost +20–40%, line speed −20–40%, defect rate 2–5% rising to 8–15%, full inspection and a complete traceability package, restricted rework | Industry-typical |
| Line ownership | 7 SMT lines and 2 THT lines in the same plant, on the same work order | Verified |
THERMAL BUDGET
Three numbers decide whether your reflowed parts survive the THT pass
Reflow first, THT secondSecond excursion bounded by J-STD-020
Selective nozzle 260–280 °C, localisedOne joint at a time
Peak ceiling 260 °C per J-STD-020Absolute, applies to every component on the board
Wave 255–265 °C, whole boardRequires a masking pallet over the SMT side
MSL floor life re-counted before the second passOver budget → bake before THT soldering
The ceiling is a component limit, not a process preference. A board that mixes a 0.4 mm-pitch BGA with a press-fit backplane connector can hold both, but only if the through-hole heat stays under the same 260 °C peak the reflow profile already respected.
WHAT ONE WORK ORDER COVERS
Six operations inside a single build package
Traceability
One work order, one record
SMT, press-fit and hand soldering post to the same work order and the same lot record, so a returned board resolves to one build history instead of three suppliers' paperwork.
Solderless
Press-fit
Compliant-pin connectors are pressed with controlled force and a support fixture. No solder joint means no solder-joint defect class for that connection.
Single pass
Pin-in-paste
Through-hole parts reflow together with the SMT side using 2–3× the paste volume, delivered by a stepped stencil or print-plus-dispense. Best when hole count per board is low.
Per joint
Three through-hole methods
Selective for localised heat, dual-wave behind a pallet for dense connector fields, hand soldering for rework and for parts that cannot take either. Allocation is decided joint by joint.
Double-sided
Two reflow passes, one carrier
The second side runs on a carrier that supports the populated first side. Board thickness from 0.4 mm; the same pallet logic protects the assembly in the THT pass that follows.
Fixed before tooling
Class locked, line not re-tuned
Changing class mid-build means re-cutting the stencil parameters, re-programming selective soldering and reconfiguring inspection. That is why the class is fixed at DFM, not at first article.
TOOLING, LEAD TIME, MINIMUM ORDER
What the sequence costs and how long it takes
| Item | Figure | Note |
|---|---|---|
| Minimum order | Chip passives 0603–2225 / SOT / SOD / MELF: 50 pcs + 30 spares. Other packages: 100 pcs + 50 spares. | Set by the component package and its reel economics; prototype quantities are quoted per project. |
| Prototype build | 1–10 pcs in 3–7 working days | Assembly lead time ex-components. |
| Small batch | 10–1,000 pcs in 5–10 working days | Assembly lead time ex-components. |
| 5,000 pcs | Approximately 3 weeks | Assembly lead time ex-components; not a general volume lead time. |
| Production, components in hand | 3–4 weeks ex-works | 3–4 weeks ex-works, then assembly lead time ex-components. |
| Long-lead semiconductors | Can add 12–26 weeks | Industry data. The bottleneck sits in the BOM, not on the line. |
| Unit premium, 5–20 pcs | +30–40% on unit price | Stencil, programme, first article and changeover time spread over very few boards. |
| Unit premium, 101–499 pcs | +5–15% on unit price | Same setup, more boards to carry it. |
| NRE | Commonly USD 0–150, waived on most projects | Quoted with the build, not treated as a separate profit line. |
| Pallet or carrier | USD 3,000–8,000 per design | Industry-typical. Masking apertures are cut for your specific SMT layout. |
| Selective-solder programming | USD 500–1,000 | Industry-typical. One programme per board design. |
| Economic sweet spot | Selective wins below roughly 5,000 pcs per batch; wave wins above roughly 10,000 pcs per batch | Industry-typical, measured on a typical mixed board with around 20 through-hole joints. |
MATERIALS AND CONSUMABLES
Four choices you specify, we tool for
Fixture
Pallets and carriers
Composite pallets with apertures cut to mask the SMT area while the through-hole joints are exposed. USD 3,000–8,000 per design (industry-typical); at least 0.8 mm board thickness if you also want V-CUT depaneling.
Nozzle and press
Selective nozzles and press-fit tooling
Single-point selective nozzles running 260–280 °C lead-free, plus compliant-pin insertion tooling and a support fixture that sets insertion force and keeps the board flat under the press.
Alloy
Alloy and flux
SAC305 lead-free is the default. The wave section uses spray fluxing with a preheat zone. Lead-free wave baths generate 30–50% more dross than tin-lead (industry-typical), which is a maintenance cost, not a quality difference.
Masking
Masking and fixture consumables
High-temperature masking tape and fixtures, carrier locating pins, and the moisture-barrier packaging set — barrier bag, desiccant and humidity indicator card — that closes out the lot.
Consumable choices are recorded on the work order, and component-level questions route through component sourcing while test coverage is configured with testing & inspection.
HOW YOU VERIFY THE CLASS
Locked at DFM, checked against named standards
Class written into the work order
The joint class is recorded on the work order and the operator instructions before panelisation, so it is a build input rather than an inspection opinion.
Named acceptance standards
Visual acceptance to IPC-A-610 Class 2 / Class 3, process requirements to IPC J-STD-001, rework to IPC-7711/7721.
BGA void criteria to IPC-7095
Class 2 allows ≤25% single void and ≤40% total; Class 3 allows ≤10% single and ≤25% total, measured by X-ray on the joints the project designates.
Cleanliness and management system
Ionic contamination by ROSE to IPC-TM-650 Method 2.3.25: ≤1.56 µg NaCl eq/cm² at Class 2 and ≤0.78 at Class 3, under ISO 9001:2015, IATF 16949:2016 (product design excluded) and ISO 13485:2016, whose scope is Production of PCBA.
WHERE MIXED BOARDS COME FROM
Six industries that mix SMT with through-hole
Industrial
Industrial automation
Wide-temperature parts, 10-year supply, PLC platforms that see two or three engineering changes across a 15-year life.
MedicalMedical devices
Lot-level traceability and validation documents; any process change re-opens verification.
AutomotiveAutomotive & EV
Thick-copper power stages, press-fit connectors, −40…+125 °C cycling and PPAP documentation.
ConsumerConsumer electronics & IoT
Weekly iterations, cost steps, and radio modules that need antenna and shielding decisions early.
EnergyEnergy, power & grid
2–6 oz copper, UL 94V-0 materials, 15–25 year field life and very high recall cost.
TelecomTelecom & data centre
112 Gbps PAM4 signal integrity, large-board warpage, and rework access around high-density BGA.
CASE EVIDENCE
What changed on a six-layer power board
Nordic EV charging module brand · 6-layer power board
Selective soldering replaced hand touch-up
A Nordic EV charging module brand had a 6-layer, 3 oz power board whose through-hole joints were being hand-soldered after reflow. Rework rate on those joints was 4.1%.
We moved the joints to robot selective soldering with a programmed single-point nozzle and a support fixture, keeping the through-hole heat localised so the reflowed SMT parts on the same board were untouched.
Joint rework rate4.1% → 0.3%
Copper weight3 oz
Process changeHand solder → selective
Anonymised: customer type, region, constraint, result.
REQUEST A QUOTE
Send the board, the BOM and the joint class
Layer count, through-hole joint count, connector type and the acceptance class are enough for us to tell you whether selective, wave, press-fit or pin-in-paste is the right route — and what it costs.
Reply within one business day
Mixed-technology quotes are priced from your files, volume and acceptance class.