A SOJ package is a small-outline surface-mount package whose leads curl inward under the body in a J shape, almost always on 1.27 mm pitch. It was the default package for SRAM and DRAM through the 1990s, and it is now legacy silicon that still ships from stock. One warning up front: the number in “300-mil SOJ” describes the lead row, not the plastic body, and that misreading causes most SOJ footprint errors.

Key takeaways

• SOJ stands for small outline J-lead. JEDEC defines it as a surface-mount package built to the small-outline concept with the leads formed into a J.
• Pitch is 1.27 mm on every mainstream SOJ family. The 12 mm metric outline MO-123 is the exception at 0.80 mm.
• On a 32-pin 300-mil SOJ the plastic body measures 6.48 – 6.99 mm across, while the leads span 8.38 – 8.64 mm overall.
• Standoff is 0.64 mm minimum, several times that of a narrow SOIC, which changes cleaning, coating and rework.
• J-lead feet sit partly under the body. IPC-A-610 covers them in section 8.3.7, and hidden-joint verification usually means X-ray.
• The same 1 Mb SRAM die is 3.71 mm tall in a 400-mil SOJ and 1.20 mm tall in TSOP I. That gap is why SOJ lost.

[IMAGE 1: cross-section comparing a J-lead curling under the package body with a gull-wing lead landing beside it | alt: “SOJ package J-lead cross-section compared with a gull-wing SOIC lead”]

What a SOJ package is, and how J-leads differ from gull wings

JEDEC’s definition runs to one sentence: a surface-mount package that follows the small-outline concept and has its leads formed into a J configuration. Everything practical about the package follows from that lead form.

A gull-wing lead extends outward and lands beside the body. A J-lead bends down and folds back underneath, so the foot sits beneath the plastic. Two consequences matter to a designer. The land pattern is narrower than the equivalent gull-wing part, and the solder joint is partly hidden from a camera.

The same lead form on four sides is the PLCC, also registered as QFJ. SOJ keeps leads on the two long sides only, which is why it was adopted almost exclusively for memory. TopLine’s SOJ sample library records how far that specialisation went: DRAM parts used 20 leads on a 26-position body, or 24 leads on a 28-position body, with the surplus lead positions simply omitted.

J-leads also survive handling. Bent leads before placement are routine on fine-pitch gull-wing parts and rare on SOJ, which is part of why the package outlived its pitch.

SOJ package dimensions: what “300 mil” and “400 mil” actually measure

Two widths dominate. The AS7C31024B datasheet from Alliance Semiconductor (v1.2, 24 March 2004) specifies both for the same 32-pin die, which makes it a clean side-by-side reference rather than a comparison across vendors.

Symbol	What it measures	300-mil SOJ	400-mil SOJ
e	Lead pitch	1.27 mm BSC (.050 BSC)	1.27 mm BSC (.050 BSC)
D	Body length, 32 pins	20.83 – 21.08 mm	20.83 – 21.08 mm
E	Plastic body width	6.48 – 6.99 mm	8.99 – 9.60 mm
E1	Lead row dimension	7.49 – 7.75 mm	10.03 – 10.29 mm
E2	Overall span across leads	8.38 – 8.64 mm	11.05 – 11.30 mm
A	Overall height	3.25 – 3.68 mm	3.35 – 3.71 mm
A1	Standoff	0.64 mm min	0.64 mm min
A2	Body thickness	2.41 – 2.67 mm	2.67 – 2.92 mm
B	Upper lead width	0.66 – 0.81 mm	0.66 – 0.81 mm
b	Formed lead width	0.41 – 0.51 mm	0.38 – 0.51 mm
c	Lead thickness	0.18 – 0.25 mm	0.18 – 0.33 mm

Table 1. 32-pin SOJ dimensions from Alliance Semiconductor AS7C31024B v1.2. The drawing is inch-controlled; millimetre values are converted.

Read the E, E1 and E2 rows together. On the 300-mil part the body is 6.48 – 6.99 mm wide, E1 lands at 7.49 – 7.75 mm, and the outermost lead span reaches 8.38 – 8.64 mm. The 0.300 inch that names the package is E1, not the body. Draw a footprint to the body width and every pad ends up inboard of the leads.

Note also that the drawing carries two lead-width symbols, B and b, with different values. Check a candidate footprint against both before releasing it.

The 0.64 mm minimum standoff is the other number worth keeping. It leaves a real gap under the body, which helps cleaning but also means conformal coating and underfill flow differently than under a low-standoff package.

[IMAGE 2: dimensioned end view of a 32-pin SOJ with E, E1, E2 and A called out | alt: “SOJ package dimensions showing body width, lead row spacing and overall lead span”]

Every JEDEC SOJ registration, by body width and pin count

JEDEC Publication 95 registers SOJ under more than a dozen separate outlines. The index by device type, updated March 2026, lists the following under the small-outline family.

Registration	Family description	Registered pin counts
MO-061	9.6 mm (.400″) body width SOJ	28, 32, 36, 40, 44
MO-063	9.0 mm (.350″) body width SOJ	22
MO-065	7.62 mm (.300″) body width SOJ	24, 26
MO-077	7.62 mm (.300″) body width SOJ	24, 25, 28, 32
MO-088	7.62 mm (.300″) body width SOJ	14, 16, 18, 20, 24, 28
MO-091	9.0 mm (.350″) body width SOJ	26, 28
MO-105	TSOJ	22, 24, 28
MO-119	SOJ .300″ body width (issue B, May 1992)	24, 28, 32, 36
MO-120	SOJ .350″ body width (issue B, May 1992)	24, 28, 32, 36
MO-121	SOJ .330″ body width (issue B, May 1992)	24, 28, 32, 36
MO-123	SOJ 12 mm body, 0.80 mm pitch (issue A, June 1991)	64
MO-124	SOJ 12.70 mm body, 1.27 mm pitch (issue B, January 1994)	32, 34, 36, 40, 70
MO-181	SOJ metric, 16 mm body width	40
MO-199	LSOJ	28, 32, 36, 40, 42, 44, 50, 54, 70
MO-200	SOJ 2-high / 4-high (stacked)	32, 44

Table 2. SOJ outlines registered in JEDEC Publication 95, per the index by device type updated 03/26.

Three things fall out of that list. Registered body widths run from 7.62 mm to 16 mm, so “SOJ” on its own identifies almost nothing. MO-123 is the single family registered at 0.80 mm pitch rather than 1.27 mm. And MO-200 registers stacked 2-high and 4-high SOJ, a density trick from the era before memory moved to stacked die inside one package.

SOJ footprints, solder joints and inspection

IPC-7351B treats J-lead components as their own family. Toe fillet extensions match gull-wing values at 0.55, 0.35 and 0.15 mm for the Most, Nominal and Least density levels, but the heel extension is 0.10, 0.00 and −0.10 mm because the heel sits under the body rather than out in the open. Side extensions stay at 0.05, 0.03 and 0.01 mm.

That negative heel value is the whole story of the package in one number. Pad copper does not extend inward under the plastic, so the joint forms around the outside of the curl and the heel region is invisible from above.

IPC-A-610 handles the consequence in section 8.3.7 with its own acceptance table for J-lead components, separate from the gull-wing criteria in 8.3.5. Automated optical inspection can confirm placement, orientation and bridging on a SOJ, but it cannot see the part of the joint that carries the mechanical load. For Class 3 work, plan on X-ray or an agreed alternative method rather than assuming AOI covers it.

SOJ vs TSOP: why memory moved on

The AS7C31024B ships the same die in SOJ and in TSOP I, so the trade is measurable without changing any other variable.

Parameter	SOJ 400-mil	SOJ 300-mil	TSOP I, 8 × 20 mm
Lead pitch	1.27 mm	1.27 mm	0.50 mm nominal
Maximum height	3.71 mm	3.68 mm	1.20 mm
Maximum length	21.08 mm	21.08 mm	20.20 mm (Hd)
Maximum width across leads	11.30 mm	8.64 mm	8.10 mm (body E)
Envelope area (derived)	238 mm²	182 mm²	164 mm²

Table 3. Same 32-pin, 1 Mb SRAM die in three packages, from AS7C31024B v1.2. Envelope area is derived as maximum length × maximum width.

Moving that die from a 400-mil SOJ to TSOP I cuts the board envelope by about 31 percent and the height by more than two thirds. On a module carrying parts on both sides of a card, that decides the product. The cost is 0.50 mm pitch and its assembly tolerances.

[IMAGE 3: a 32-pin SOJ and a 32-pin TSOP I drawn to the same scale, side and top views | alt: “SOJ package compared to TSOP I package height and board area”]

Sourcing SOJ parts today

SOJ has not vanished, but the stock position is thin and uneven. Alliance Memory still catalogues asynchronous SRAM in 32-pin SOJ, and distributor listings show the pattern clearly: at the time of writing DigiKey listed AS7C1024B-15JCN, a 1 Mb 32-SOJ SRAM, at 103 units in stock and USD 7.38 each, while several neighbouring SOJ order codes in the same family showed zero inventory.

Cross-references exist where the part is still made. Alliance Memory’s selection guide maps its 32-pin SOJ 1 Mb SRAM, AS7C1024C-xxJIN, against Cypress CY7C1019D and ISSI IS61C1024AL order codes. Confirm the width, since that family is offered in both 300-mil and 400-mil SOJ, and the two are not footprint compatible.

SOJ design and assembly mistakes

• Building the footprint from the body width. The mil figure names the lead row, and the overall lead span is wider again — 8.38 – 8.64 mm on a 300-mil 32-pin part.
• Ordering the wrong width. A 300-mil and a 400-mil SOJ of the same device carry the same pin count, the same pitch and nearly the same length, and they will not swap.
• Specifying AOI-only inspection. Section 8.3.7 of IPC-A-610 exists because part of a J-lead joint is not visible; for Class 3, agree the verification method in advance.
• Copying gull-wing heel extensions into a J-lead footprint. IPC-7351B sets the J-lead heel at 0.10, 0.00 or −0.10 mm, not 0.45, 0.35 or 0.25 mm.
• Assuming iron-and-braid rework. Plan hot air and a body-sized nozzle, or accept that a failed part means a scrapped board.
• Designing a new product around a SOJ order code without checking stock depth across the whole family first.

SOJ package FAQ

What does SOJ stand for?

SOJ stands for small outline J-lead. JEDEC defines it as a surface-mount package that conforms to the small-outline concept and has its leads formed into a J configuration, folding down and back under the package body. Some vendors write it SOIJ or J-leaded small outline IC package.

What is the difference between SOJ and SOIC?

Lead form. SOIC uses gull-wing leads that extend outward and land beside the body; SOJ curls the leads under the body. Both use 1.27 mm pitch in their mainstream families, but SOJ is taller, its footprint is narrower relative to the body, and part of its solder joint is hidden from view.

What is the SOJ pin pitch?

1.27 mm, equal to 50 mil, across every mainstream SOJ family registered by JEDEC. The one documented exception in the Publication 95 index is MO-123, a 12 mm body 64-lead outline registered at 0.80 mm pitch in June 1991.

Is a 300-mil SOJ body 300 mil wide?

No. On the AS7C31024B 32-pin part the plastic body is 0.255 – 0.275 inch wide, the E1 lead row dimension is 0.295 – 0.305 inch, and the overall span across the leads reaches 0.330 – 0.340 inch. The name tracks E1. Always dimension a footprint from the drawing, not the package name.

Are SOJ packages still available?

Yes, in asynchronous SRAM from suppliers such as Alliance Memory, and through Renesas and ISSI order codes. Stock depth varies sharply by order code, with some listings showing hundreds of units and adjacent ones showing none. Treat it as a legacy supply line rather than a package to specify in a new design.

What to do if a SOJ part is on your BOM

For an existing board, pull the package drawing for the exact order code and confirm E1 and E2 against the released footprint before you buy anything. The 300-mil and 400-mil variants of the same device are the failure mode to rule out first.

For a new design, do not start here. Take the same die in TSOP or BGA, accept the finer pitch, and spend the saved 31 percent of board envelope and two thirds of the height somewhere useful. Keep SOJ for the case where a legacy footprint is fixed and a drop-in replacement is the whole requirement.