Wide-creepage surface-mount opto-isolator: 8 mm SO6L and stretched SO-8 packages for reinforced isolation on a circuit board
Surface-mount opto-isolators in 8 mm packages · SO6L and stretched SO-8 outlines, external creepage versus the creepage left on the board, internal insulation thickness, VIORM and VIOTM
An opto-isolator in a widened surface-mount package, such as the SO6L or the stretched SO-8, spreads its input and output leads far enough apart that the package body itself gives 8 mm between them, so a reinforced isolation barrier can be built on a densely packed board without a through-hole DIP part. Buying one means reading three numbers: the external creepage and clearance of the package, the distance through the insulation inside it, and the working and transient voltages it is certified for. The creepage that matters in the end is the one left after the part is soldered to the board.
Opto-isolators (phototransistor and logic-output optocouplers) in wide-body surface-mount packages, such as SO6L and stretched SO-8, rated for 8 mm external creepage and clearance, together with how their creepage is kept on the printed circuit board. Optocouplers and digital isolators as a general product, with current transfer ratio, speed and the IEC 60747-5-5 standard, are covered on the Optocoupler / isolator page; DIN-rail boards carrying 8 to 16 optocoupler channels are covered on the DIN-rail optocoupler isolation board page. Faraday optical isolators for lasers and fibre links, solid-state relays and isolated gate drivers are outside this page.
CNFX editorial research · Sources checked October 12, 2026 · 3 sources
Creepage, clearance and through-insulation of the SO6L and stretched SO-8 packages
Both wide-body packages reviewed give 8 mm outside the body; they differ by a factor of five in the distance through the insulation inside.
Editorial calculation: Toshiba's 0.4 mm minimum internal isolation thickness is five times Broadcom's 0.08 mm minimum internal plastic gap, so where an equipment standard sets a minimum distance through solid insulation for reinforced insulation, check that figure for each package rather than the matching 8 mm external values. [1][2]
Toshiba describes the TLP385 as an SO6L part with a small, thin package compared with a standard DIP, aimed at high-density surface mounting in programmable controllers, AC adapters and I/O interface boards; its VDE approval to EN 60747-5-5 and EN 62368-1 applies only to the option (D4) version. [1] Broadcom's EN 60747-5-5 ratings likewise apply to options 060E and 560E. [2]
Order the safety-approved option code, not the base part number, when the end product needs the EN 60747-5-5 (VDE) ratings; both data sheets tie those ratings to an option.
02
Working voltage, partial-discharge test and transient rating of a stretched SO-8 part
Broadcom gives the ACPL-K43T a maximum working insulation voltage VIORM of 1140 Vpeak and a highest allowable transient overvoltage VIOTM of 8000 Vpeak for 60 s, for pollution degree 2 and installation classes I–IV up to 600 Vrms mains and I–III up to 1000 Vrms. [2]
Every part is tested at VPR = 1.875 × VIORM = 2137 Vpeak for 1 s with partial discharge under 5 pC, and type and sample tests use 1.6 × VIORM = 1824 Vpeak for 10 s; in addition, each optocoupler is proof-tested at 6000 Vrms or more for 1 second under UL 1577. [2] Editorial calculation: 1140 Vpeak divided by √2 is about 806 V rms for a sinusoidal working voltage. The safety limiting values, which apply in the event of a failure, are a case temperature of 175 °C, an input current of 230 mA and an output power of 600 mW. [2]
03
Keeping the 8 mm once the part is soldered: pads, land pattern and pollution degree
In an InCompliance magazine example, Don MacArthur takes pollution degree 2, the product's working voltage and the material group of the optocoupler and board, arrives at a required 8 mm creepage, picks a part rated for it, and then finds that the PCB pads shorten the creepage to 7.2 mm. [3]
His figure note explains why: pad-to-pad spacing on the board only needs the creepage for material group I, but copper pads shared with the optocoupler shorten the path across the optocoupler's own material group IIIx surface. He lists the groups as I for CTI of 600 and above, II for 400 to below 600, IIIa for 175 to below 400 and IIIb for 100 to below 175. [3] Broadcom puts the ACPL-K43T in group IIIa with CTI 175 V. [2]
Editorial calculation: the example loses 0.8 mm, a tenth of the 8 mm the package provides. [3] Editorial note: on the layout, measure creepage pad edge to pad edge across the package outline, and do not let a land pattern that extends the pads toward the body of an SO6L or stretched SO-8 part eat into the 8 mm.
Ask the supplier for the package outline with lead span and the recommended land pattern, and check the pad-to-pad creepage on your board against the requirement before the board is released.
04
Send the insulation requirement, the board layout and the signal
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Insulation: [basic or reinforced; working voltage; pollution degree; material group; required creepage and clearance; distance through insulation]
Approvals: [UL 1577; EN 60747-5-5 option code; EN 62368-1]
Package: [SO6L; stretched SO-8; lead span; land pattern]
Signal: [transistor or logic output; CTR or data rate; CMR]
Environment: [operating temperature; automotive qualification]
Quantity and packing: [tape and reel]
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
What creepage does an SO6L opto-isolator give?
Toshiba's TLP385 in a 4-pin SO6L lists 8.0 mm minimum creepage and clearance and 0.4 mm minimum internal isolation thickness. [1]
Is the internal insulation the same in all 8 mm packages?
No. Broadcom's stretched SO-8 ACPL-K43T lists a 0.08 mm minimum internal plastic gap against Toshiba's 0.4 mm for the SO6L TLP385, though both give 8 mm outside. [2][1]
Can the PCB reduce an optocoupler's creepage?
Yes. In an InCompliance example, pads on the board cut a required 8 mm creepage to 7.2 mm. [3]
What working voltage is a stretched SO-8 optocoupler rated for?
Broadcom rates the ACPL-K43T at VIORM 1140 Vpeak and VIOTM 8000 Vpeak under EN 60747-5-5 options 060E and 560E. [2]
Sources and what still needs a direct check
Sources checked 2026-10-12. Toshiba and Broadcom data sheets give the package insulation data for one part each; Don MacArthur's InCompliance magazine column shows how board layout changes the result. The end product's safety standard sets the required distances.
