An SO-16 package is a 16-lead gull-wing surface-mount body on 1.27 mm pitch, and it ships in two widths that are not interchangeable: a 3.90 mm narrow body with a 6.00 mm lead span, and a 7.50 mm wide body with a 10.30 mm lead span. The pinout is not standardized. This guide gives both dimension sets, the land pattern data, and the suffix codes that separate the two.

Key Takeaways

• Two variants share the name: narrow body (JEDEC MS-012 AC, 150 mil class) and wide body (JEDEC MS-013 AA, 300 mil class).
• Lead pitch is 1.27 mm BSC in both. Lead span is the fast way to tell them apart: 6.00 mm versus 10.30 mm.
• Maximum seated height differs by 0.90 mm — 1.75 mm narrow, 2.65 mm wide — which pushes the wide body into a different J-STD-020 reflow bin.
• The package fixes mechanics only. Supply and ground can sit on any pin, so never carry a pinout assumption across manufacturers.
• Suffix codes settle it faster than a datasheet search: TI D versus DW, Analog Devices RZ versus RWZ, Microchip SL versus SO.

SO-16, SOIC-16, SOP-16: what the names actually fix

SO stands for Small Outline. In current datasheets, SO-16 and SOIC-16 point at the same JEDEC-registered outline family, registered as MS-012 for the narrow body and MS-013 for the wide body. Vendor marketing names vary; the registration number does not.

The label tells you three facts: sixteen leads, 1.27 mm pitch, gull-wing formed leads. It tells you nothing about body width, function, thermal resistance, or pin assignment. Two parts described as SO-16 can differ by 4.30 mm across the leads.

Two lookalikes cause most of the sourcing errors. EIAJ/JEITA SOP-16 is a separate registration with its own tolerances, not a synonym. QSOP-16 (0.635 mm pitch) and SSOP-16 (0.65 mm pitch) carry the same pin count and a similar silhouette in a BOM line, and neither will sit on an SO-16 land pattern.

[IMAGE 1: annotated top and side view of a narrow-body and a wide-body SO-16 side by side, with E, E1, D and A called out | alt: “SO-16 package dimensions comparison, narrow body and wide body outlines”]

SO-16 package dimensions: narrow body versus wide body

SO-16 package dimensions use 1.27 mm lead pitch in both variants. The narrow body measures 3.90 mm wide with a 6.00 mm lead span, 9.90 mm long, and 1.75 mm maximum height. The wide body measures 7.50 mm wide with a 10.30 mm lead span, 10.30 mm long, and 2.65 mm maximum height.

Symbol	Dimension	Narrow body (MS-012 AC)	Wide body (MS-013 AA)
A	Overall height, max	1.75 mm	2.65 mm
A1	Standoff	0.10 – 0.25 mm	0.10 – 0.30 mm
b	Lead width	0.31 – 0.51 mm	0.31 – 0.51 mm
c	Lead thickness	0.17 – 0.25 mm	0.20 – 0.33 mm
D	Body length	9.80 – 10.00 mm	10.10 – 10.50 mm
E	Lead span, overall	5.80 – 6.20 mm	10.00 – 10.65 mm
E1	Body width	3.80 – 4.00 mm	7.40 – 7.60 mm
e	Lead pitch	1.27 mm BSC	1.27 mm BSC
L	Foot length	0.40 – 1.27 mm	0.40 – 1.27 mm
θ	Lead foot angle	0° – 8°	0° – 8°

Table 1. Controlled dimensions for the two SO-16 variants. Confirm against the JEDEC revision your supplier cites on the mechanical drawing.

Read the drawing notes, not just the numbers. Standard SOIC notes exclude mold flash from D and interlead flash from E1, typically capping protrusion at 0.15 mm per side on D and 0.25 mm per side on E1. Load the un-flashed values into your pick-and-place package definition or the vision system will reject good parts.

Lead coplanarity is specified at 0.10 mm maximum. That single figure decides whether a reel of parts will solder on a warped board, and it is the first thing to measure when one corner of a run shows open joints.

Which SO-16 is on your BOM? A 30-second check

1. Measure across the lead tips with calipers. Roughly 6 mm means narrow body; roughly 10.3 mm means wide body. Body width alone is easy to misjudge by eye.
2. If you only have a part number, decode the package suffix using Table 2. This is faster than opening the datasheet and works on a purchase order.
3. If the suffix is unfamiliar, open the mechanical drawing and read dimension E. Ignore the marketing name at the top of the page.

Manufacturer	Narrow body (150 mil class)	Wide body (300 mil class)
Texas Instruments	D	DW
Analog Devices	RZ (SOIC_N)	RWZ (SOIC_W)
Microchip	SL	SO
onsemi	SOIC-16	SOIC-16W
NXP	D (SOT109)	DW (SOT162)

Table 2. Package suffix decoder. Verify against each manufacturer’s current package code table before releasing a BOM.

Substituting D for DW on an assembled board does not work. The land patterns differ by more than 4 mm across the pad rows, so the wide part bridges nothing and the narrow part floats between the pads. Treat the two as separate line items with separate approvals.

SO-16 pinout: what is standardized and what is not

Pin numbering follows one rule. Viewed from above with the pin 1 marker at the upper left, numbering runs counterclockwise: pin 1 to pin 8 down the left side, pin 9 to pin 16 up the right side. Pin 8 and pin 9 sit diagonally opposite pin 1 and pin 16.

Pin 1 is identified by a molded dimple, a laser dot, a beveled body edge, a half-moon notch at one end, or some combination. When markings disagree, the datasheet mechanical drawing is authoritative.

Function assignment is not standardized at all. The package registration says nothing about where power lands, and the four common SO-16 parts below put supply and ground in four different places.

Part family	Function	Supply pin	Ground / return pins
74HC595 shift register	Logic	Pin 16 (VCC)	Pin 8 (GND)
ULN2003A driver array	Sink driver	None (open collector)	Pin 8 (GND), pin 9 (COM clamp)
MAX232 line driver	RS-232 interface	Pin 16 (VCC)	Pin 15 (GND)
Quad digital isolator	Isolation	Pins 1 and 16 (two rails)	Split: side 1 on pins 1–8, side 2 on pins 9–16

Table 3. Four widely used SO-16 parts, four different power arrangements. Confirm every assignment against the specific datasheet revision.

Isolators are the case that catches people out. A wide-body SO-16 isolator dedicates the whole left column to one voltage domain and the whole right column to the other, so the barrier runs down the middle of the package. Copper poured under the body defeats the point; keep the plane split aligned to the package centerline.

[IMAGE 2: top-view pin map of a 16-lead SO package showing counterclockwise numbering and pin 1 markers | alt: “SO-16 pinout diagram showing pin 1 marker and counterclockwise pin numbering”]

Land pattern, stencil, and assembly

IPC-7351B names the two footprints unambiguously: SOIC127P600X175-16N for the narrow body and SOIC127P1030X265-16N for the wide body. The trailing letter is the density level — L for least (high-density boards), N for nominal, M for most (high-reliability and hand assembly).

Generate the pads with an IPC calculator rather than copying them. Nominal-density narrow-body pads land near 0.60 mm wide by 1.55 mm long. Moving from N to M adds toe extension, which buys inspectable fillets at the cost of about 1 mm of overall length.

Stencil design is undemanding at this pitch. With a 0.12 mm foil and a 0.60 mm by 1.55 mm aperture, the area ratio is (0.60 × 1.55) ÷ (2 × (0.60 + 1.55) × 0.12) = 1.80, comfortably above the 0.66 minimum in IPC-7525. A 1:1 aperture works; there is no need to reduce it.

At 1.27 mm pitch, SO-16 remains hand-workable. Drag soldering with flux and a chisel tip clears a full row in a few seconds, which matters for prototype rework and for field repair of low-volume instruments.

Thermal: run the number, do not trust the package

Junction-to-ambient resistance for an SO-16 is a property of the board, not the package. Typical datasheet values run roughly 73 to 110 °C/W for the narrow body and 60 to 90 °C/W for the wide body, and the spread inside those ranges comes almost entirely from whether the number was measured on a JESD51-3 single-layer board or a JESD51-7 four-layer board.

Worked example, narrow-body SO-16 driver:

• Dissipation: 0.45 W. Ambient: 70 °C. Maximum junction temperature: 125 °C.
• Four-layer board, θJA = 90 °C/W → ΔT = 0.45 × 90 = 40.5 °C → Tj = 110.5 °C. Margin: 14.5 °C.
• Single-layer board, θJA = 130 °C/W → ΔT = 58.5 °C → Tj = 128.5 °C. Over limit by 3.5 °C.

Same part, same power, opposite verdicts. Before you accept a thermal margin, find the note under the θJA table that names the test board. If the datasheet quotes only one value, assume the more favorable board and derate.

Moisture and reflow: where narrow and wide part ways

J-STD-020 sets the classification reflow temperature from package thickness and body volume, and the two SO-16 variants fall on opposite sides of the 2.5 mm thickness boundary.

	Narrow body	Wide body
Maximum thickness	1.75 mm	2.65 mm
Approximate body volume	9.9 × 3.9 × 1.75 ≈ 68 mm³	10.3 × 7.5 × 2.65 ≈ 205 mm³
J-STD-020 thickness bin	1.6 – 2.5 mm	≥ 2.5 mm
Classification peak temperature	260 °C	250 °C

Table 4. Reflow classification consequence of the height difference. Confirm the actual figure on the part label and the J-STD-020 revision in force.

The practical effect: a profile validated at 260 °C peak for narrow-body logic can exceed the classification temperature of a wide-body part on the same panel. Check the MSL and peak temperature printed on the dry pack before you reuse a profile.

Floor life follows the MSL rating. An MSL 3 part allows 168 hours out of the bag at 30 °C and 60% relative humidity; exceed it and the part needs a bake before reflow. Popcorning in a wide body is more damaging than in a narrow one because there is more trapped moisture under a larger die paddle.

SO-16 versus the smaller 16-pin alternatives

Package	Pitch	Body (W × L)	Max height	Lead span	Board area
SO-16 narrow	1.27 mm	3.9 × 9.9 mm	1.75 mm	6.0 mm	≈ 59 mm²
SO-16 wide	1.27 mm	7.5 × 10.3 mm	2.65 mm	10.3 mm	≈ 106 mm²
QSOP-16 (MO-137)	0.635 mm	3.9 × 4.9 mm	1.75 mm	6.0 mm	≈ 29 mm²
SSOP-16 (MO-150)	0.65 mm	5.3 × 6.2 mm	2.00 mm	7.8 mm	≈ 48 mm²
TSSOP-16 (MO-153)	0.65 mm	4.4 × 5.0 mm	1.20 mm	6.4 mm	≈ 32 mm²

Table 5. Board area is lead span × body length, the rectangle the footprint actually consumes.

Decision rules:

• Default to SO-16 narrow for 16-pin logic, drivers, and interface parts where 59 mm² is affordable and hand rework is likely.
• Choose SO-16 wide only when you need the creepage and clearance of a 10.3 mm span, or when the die will not fit a 3.9 mm body.
• Move to TSSOP-16 to halve the area and drop under a 1.2 mm height limit, accepting 0.65 mm pitch and harder rework.
• Reach for QSOP-16 when the board is dense but the enclosure is not height-constrained; it keeps the 6.0 mm span and cuts length in half.

Five mistakes that cause respins

• Specifying “SOIC-16” in a BOM without the width. Purchasing buys whichever is cheaper and the board will not accept it.
• Copying a footprint from an old project without checking the density level. An L-density pad set gives inspectors no visible toe fillet.
• Reusing a pinout across vendors because the pin count matches. Second sources for a function are rarely pin-compatible.
• Pouring a continuous ground plane under a wide-body isolator, which shortens the creepage path the package was chosen for.
• Quoting a single-layer θJA in a thermal review. The margin looks fine on paper and disappears on the bench.

Frequently asked questions

Is SO-16 the same as SOIC-16?

In current practice, yes. Both names refer to the 16-lead small outline family registered under JEDEC MS-012 (narrow) and MS-013 (wide). SO is the older term inherited from the original Philips and Signetics packages. The distinction that matters is narrow versus wide body, not SO versus SOIC.

What is the pin pitch of an SO-16 package?

Lead pitch is 1.27 mm BSC, equal to 0.050 inches, and it is identical for the narrow and wide bodies. BSC means basic spacing between centers, a theoretically exact value with tolerance applied to the position of the lead group rather than to the pitch itself.

What is the difference between SO-16 narrow and SO-16 wide?

Body width is 3.90 mm versus 7.50 mm, lead span is 6.00 mm versus 10.30 mm, and maximum height is 1.75 mm versus 2.65 mm. Pitch and pin count are the same. The footprints are not interchangeable, and the wide body carries a lower reflow classification temperature.

Does the SO-16 package have a standard pinout?

No. The registration controls mechanical outline only. Pin 1 sits at the upper left in top view and numbering runs counterclockwise, but supply, ground, and signal assignments are chosen by the device manufacturer and vary between parts that share the package.

Can SO-16 be hand-soldered?

Yes. At 1.27 mm pitch it is one of the easier surface-mount packages to hand-assemble. Flux the leads, tack two opposite corners, then drag solder each row with a chisel tip. Use an M-density footprint if hand assembly is planned, since the longer pads give the iron somewhere to land.

What to do next

Pick the narrow body unless a specific requirement forces the wide one. Isolation ratings, creepage over 8 mm, and oversized die are the requirements that justify the extra 47 mm² of board area; nothing else usually does.

Then do three things before the design review: write the full package suffix into the BOM line, generate the land pattern from IPC-7351B at N or M density rather than copying it, and check the reflow classification temperature on the dry pack against your oven profile. Those three steps remove the failures that show up after the first assembly run.