Automated printed circuit board assembly line for mixed SMT and through-hole boards

01

Decide which through-hole parts are inserted automatically

Universal Instruments' Radial 88HTi datasheet lists a throughput of 20,000 cph for radial-lead parts (capacitors, LEDs, transistors, resistors, connectors), with single, dual, triple and quad-span tooling covering lead spans of 2.5 to 10.0 mm, 20 to 100 component inputs in steps of 20, and servo heads that insert at any angle in 1° steps. [1]

The same datasheet gives board sizes of 102 × 80 mm to 483 × 406 mm with automatic loading (51 × 51 mm to 600 × 600 mm manual), a 2-second board exchange in pass-through, reliability of 300 ppm or better for single and dual span and 400 ppm for triple and quad span, a single-phase 180–246 V, 1,150 VA supply, and a programmable insertion height to avoid damaging surface-mount components already on the board. [1]

Editorial calculation: at 20,000 cph, one insertion takes 0.18 s; a board with 60 radial parts would take about 11 s of insertion before board exchange. Compare that with the SMT section's cycle time for the same board to see whether the insertion stage paces the line.

Give the supplier the board size and thickness, the list of through-hole parts with lead spans and package type (radial, axial, connectors, odd-form), parts per board, boards per hour, which parts may stay manual, the solder alloy, and the test steps required at the end of the line.

02

Solder the leaded parts after reflow without eroding the copper

In a paper on lead-free selective soldering, ACE Production Technologies reports that Sn-Ag-Cu dissolves copper at an average 0.020 mils per second of contact time, double the 0.010 mils/s of Sn-Cu-Ni, against 0.005 mils/s for tin-lead, and that the recommended maximum cumulative through-hole contact time, including wave soldering and rework, is 45 seconds. [3]

ACE writes that with sustained topside preheat the solder pot temperature can be lowered from 300–320 °C to 260–280 °C, that the best results come with topside board temperature of 110–120 °C, and that fluxes must withstand topside temperatures of 130 °C or higher and solder at 280 °C or higher for at least 3–4 seconds of contact. It recommends that pot analysis keep copper below 1.0%, iron below 0.02% and lead below 0.1% by weight. [3]

Kurtz Ersa's VERSAFLOW 3/66 inline selective soldering platform takes boards of 63.5 to 610 mm width and 127 to 610 mm length, up to 5 kg (15 kg optional), with 120 mm top and 60 mm bottom clearance, up to three soldering modules with one or two single-wave pots holding 13 kg of solder each, up to five bottom preheat modules, and drop-jet fluxing with up to four heads; the machine is 2,950 × 1,900 × 1,650 mm. [2]

Editorial calculation: at ACE's 0.020 mils/s for Sn-Ag-Cu, 45 s of cumulative contact would remove about 0.9 mil (about 23 µm) of copper, in line with ACE's report that rework can consume as much as 0.8 mils, about half the average copper thickness. [3]

03

In-house or integrated through-hole stages after SMT

Ask each supplier which through-hole stages (insertion, selective or wave soldering, test) they supply themselves and which they integrate from other makers, and how boards and data pass between the SMT and through-hole sections.

04

From the SMT section through fluxer, preheat and solder pot to final test

05

Which stage limits the line? Board size and cycle time per machine

06

Send the board, parts and soldering data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Board: [size; thickness; panel; surface finish]
SMT: [parts per board; smallest package]
Through-hole: [part list; lead spans; packages; manual parts]
Soldering: [alloy; selective or wave; preheat; contact-time limit]
Output: [boards per hour]
Test: [AOI; ICT; functional]

See manufacturer records Send an enquiry through CNFX