A J-lead package curls its leads back underneath the body, so most of the solder joint sits where you cannot see it. On a 44-pin PLCC the externally visible band of the joint is between 0.37 mm and 0.57 mm wide, calculated from the package drawing. Everything else about inspecting, reworking and laying out a J-lead package follows from that one fact.

Key takeaways

• J-lead means PLCC and SOJ. The lead exits the body, turns down, then curls back inward under the package.
• The JEDEC numbers most references quote are out of date. MO-052 was replaced by MS-016 and MO-061 was rescinded in favour of MS-027.
• Pitch is 1.27 mm across the whole family. Lead width is 0.66 mm to 0.81 mm and lead thickness 0.33 mm to 0.53 mm on both PLCC drawings checked here.
• IPC-A-610H gives J leads their own criteria set in clause 8.3.7 and Table 8-7, separate from the gull-wing tables.
• Coplanarity is specified at 0.10 mm on the package drawings, which is what makes a hidden joint recoverable at all.
• Design new boards around gull-wing or leadless parts. Use J-lead for socketed, field-replaceable or legacy positions.

What a J-lead package is, and which packages use one

A J-lead package is a surface-mount package whose leads are formed into a J shape: out of the body, down past the seating plane, then back in underneath the package. JEDEC defines the small-outline J-lead package as a small-outline package with leads formed into a J configuration. The two families that use it are the plastic leaded chip carrier (PLCC), with leads on all four sides, and the small-outline J-lead package (SOJ), with leads on two sides.

JEDEC gives SOJ the descriptor R-PDSO-J, which decodes as rectangular plastic dual small outline with J leads. The gull-wing equivalent carries a G in the same position. That single letter is the whole difference in the descriptor system, and it is the difference that decides how the joint forms.

The registered outlines are worth getting right, because most published summaries repeat numbers that JEDEC has since superseded.

Table 1. JEDEC registered outlines for J-lead packages, per the JEDEC MO and MS indexes

Outline	Title	Status
MO-047	Plastic Chip Carrier (PCC) family, 0.050 in leadspacing, square	Issue B, November 1988
MO-052	Plastic Chip Carrier (PCC) family, 0.050 in leadspacing, rectangular	Replaced by MS-016
MO-061	Plastic Small Outline J-Lead (SOJ), 0.400 in body family	Rescinded, replaced by MS-027
MO-063	Plastic Small Outline J-Lead (SOJ), 0.350 in body	Registered
MO-065	Plastic Small Outline J-Lead (SOJ), 0.300 in body family	Registered
MS-016	Plastic chip carrier, rectangular, 0.050 in	Registered standard
MS-018	Square plastic chip carrier, 0.050 in pitch	Registered standard
MS-023	Plastic SOJ	Registered standard
MS-027	SOJ, 0.400 in body, 0.050 in pitch (R-PDSO-J)	Issue A, March 1995

If a library part or a BOM line cites MO-052 for a rectangular PLCC, it is quoting a withdrawn outline. Ask for the MS-016 variation letter instead.

[IMAGE 1: cross-section of a J-lead package solder joint next to a gull-wing joint, showing the curl tucked under the body | alt: “Cross-section comparing a J-lead package solder joint with a gull-wing solder joint on a PCB land”]

J-lead geometry: real numbers from two package drawings

Two Renesas plastic leaded chip carrier drawings cover the square and rectangular cases and both carry JEDEC variation numbers, so they are safe to reason from.

Table 2. PLCC geometry from two JEDEC-referenced package drawings

Dimension	PLCC-32, N32.45×55 (MS-016AE)	PLCC-44, N44.65 (MS-018AC)
Shape	Rectangular, 7 and 9 leads per side	Square, 11 leads per side
Overall D (lead tip to lead tip)	12.32 to 12.57 mm	17.40 to 17.65 mm
Overall E	14.86 to 15.11 mm	17.40 to 17.65 mm
Body D1	11.36 to 11.50 mm	16.51 to 16.66 mm
Body E1	13.90 to 14.04 mm	16.51 to 16.66 mm
Overall height A	3.18 to 3.55 mm	4.20 to 4.57 mm
Lead pitch	1.27 mm	1.27 mm
Lead width	0.66 to 0.81 mm	0.66 to 0.81 mm
Lead thickness	0.33 to 0.53 mm	0.33 to 0.53 mm
Lead bend radius	1.14 mm	1.14 mm
Coplanarity	0.10 mm	0.10 mm

The lead detail is identical between the two. That is the useful part: pitch, width, thickness, bend radius and coplanarity are family constants, so a stencil and inspection recipe developed for one PLCC transfers to the next. Only the body and the lead count change.

Note the height. A PLCC-44 stands 4.20 mm to 4.57 mm tall. That is roughly four times a 1.2 mm TSSOP and it is the price of curling the lead underneath rather than out to the side.

Worked example: how much of the joint you can actually see

Take the PLCC-44 drawing. Overall dimension D runs 17.40 mm to 17.65 mm and body dimension D1 runs 16.51 mm to 16.66 mm. The lead projects beyond the body by half the difference.

Maximum projection is (17.65 − 16.51) / 2 = 0.57 mm per side. Minimum projection is (17.40 − 16.66) / 2 = 0.37 mm per side.

Run the same arithmetic on the PLCC-32 short side and you get (12.57 − 11.36) / 2 = 0.61 mm maximum and (12.32 − 11.50) / 2 = 0.41 mm minimum. Across the family, the externally visible band of a J-lead joint is roughly 0.4 mm to 0.6 mm.

Compare that with a gull-wing package, where the entire foot and its heel and toe fillets sit outside the body outline and can be measured directly. On a J lead, the contact patch, the majority of the fillet and any voiding are hidden under the package. Automated optical inspection sees the outer curl and nothing else, which is why Class 3 assemblies usually get x-ray or cross-section sampling rather than optical inspection alone.

[IMAGE 2: annotated PLCC-44 bottom view showing D, D1 and the 0.37 to 0.57 mm band of lead that projects beyond the body | alt: “PLCC J-lead package dimensions showing the narrow band of lead visible outside the package body”]

How IPC treats J-lead solder joints

IPC-A-610H, issued September 2020, does not fold J leads into the gull-wing criteria. Clause 8.3.7 covers J leads on its own, with its own dimensional table, Table 8-7.

The sub-clauses run: side overhang (A) at 8.3.7.1, toe overhang (B) at 8.3.7.2, end joint width (C) at 8.3.7.3, side joint length (D) at 8.3.7.4, maximum heel fillet height (E) at 8.3.7.5, minimum heel fillet height (F) at 8.3.7.6, solder thickness (G) at 8.3.7.7, and coplanarity at 8.3.7.8.

Flat gull-wing leads get the parallel treatment in clause 8.3.5 and Table 8-5. Round or flattened coined gull wings get clause 8.3.6 and Table 8-6, and that one adds a criterion the other two do not have: minimum side joint height (Q) at 8.3.6.8. Three lead forms, three tables, three slightly different criteria sets. Anyone writing a single inspection procedure covering all leaded SMT parts is already off-standard.

The letters are the same on J leads and gull wings, but the geometry they describe is mirrored. On a gull wing the toe points away from the body and the heel faces it. On a J lead the curl points back under the package, so the feature IPC calls the toe is the one you cannot reach with a soldering iron or a camera. That inversion is the practical content of the separate table.

For the land pattern itself, IPC-A-610H points to IPC-7351 in its summary of related documents. IPC-A-610 judges the joint. IPC-7351 sizes the copper that makes the joint possible. A Class 3 heel fillet cannot be achieved on a land that was never drawn long enough to support one.

Land pattern and stencil notes

A J-lead land has to do two jobs at once. It must extend outward past the lead tip so the outer curl has copper to wet against, and it must extend inward under the body far enough to sit beneath the contact patch. That makes the land straddle the package outline rather than sitting outside it, which is the opposite of a gull-wing land.

The 1.27 mm pitch is generous by modern standards. With a 0.66 mm to 0.81 mm lead width there is more than 0.4 mm of clearance between adjacent leads even at maximum material condition, so bridging is a paste-volume problem rather than a registration problem. Print with a 0.15 mm stencil and standard 1:1 apertures unless the assembler says otherwise.

The 0.10 mm coplanarity specification on both drawings is what makes the package work at all. A hidden joint gives you no visual warning of a lifted lead, so the tolerance has to be tight enough that every lead reaches paste without help. Check incoming coplanarity on any part that has been in stock a long time or has travelled loose in a tray.

Thermal cycling and where J-lead joints fail

The corner lead fails first, and the reason is geometric. On a PLCC-44 the outermost lead on each side sits five pitches from the row centre, or 5 × 1.27 = 6.35 mm. With a 16.5 mm body the lead row sits roughly 8.3 mm from the package centre, putting the corner lead about √(6.35² + 8.3²) = 10.5 mm from the neutral point.

Run it for the PLCC-32. The outermost lead on the nine-lead side is four pitches out, 5.08 mm, and the row sits near 6.95 mm from centre, giving about 8.6 mm. The PLCC-44 corner joint therefore absorbs roughly 22 percent more differential displacement than the PLCC-32 corner joint for the same temperature swing and the same board material.

Lead compliance is the other half. Work presented at an SMTA conference on gull-wing joint reliability summarizes the modelling consensus that solder joint lifetime in temperature cycling falls as pin stiffness rises, citing Lau and Harkins on lead and joint stiffness for plastic quad flat packs. J leads and gull wings sit at different points on that curve depending on lead length, thickness and body size, which is exactly why IPC declines to give them a shared criteria table.

Practical consequence: on a large PLCC in a cycling environment, corner-lead cracking is the expected wear-out mode, and it will not be visible from outside. Plan for periodic cross-section or x-ray sampling rather than assuming an optical pass means a healthy joint.

Sockets, rework and lifecycle

The socket is the main reason these packages survive. A PLCC socket lets a programmed device be pulled and replaced in the field without touching solder, which is why PLCC held on for EPROM, flash and programmable logic long after the pin count made sense.

That ecosystem is now thinning. The 3M 8444-11B1-RK-TP, a 44-position through-hole PLCC socket on 1.27 mm mating pitch and 2.54 mm post pitch, was listed at Digi-Key on 11 August 2026 as last time buy with a 31 March 2026 cutoff, 2,481 units remaining, at $2.14 in single quantity and $1.31 at 1,000. If a design depends on a socketed J-lead part, the socket may go end-of-life before the IC does.

Rework is harder than gull wing for the same reason inspection is. There is no toe to touch with an iron, so hot air with a matched nozzle and full preheat is the working method, and the joint quality after rework cannot be confirmed optically. Budget for x-ray on any reworked J-lead position in a Class 3 build.

SOJ is effectively finished as a design-in package. It survived longest in DRAM and SRAM, and JEDEC still carries the outlines, but new memory moved to TSOP and then to BGA decades ago. PLCC remains available and is still the sensible choice where a device must be socketed.

Mistakes that cause returns

Five J-lead problems account for most of the escapes, and four of them are settled before the board is built.

• Land drawn like a gull-wing land. If the copper stops at the package outline, the contact patch has nothing to wet against and the joint is thin under the body while looking acceptable outside it.
• Optical inspection accepted as proof. A 0.4 mm visible band cannot tell you whether the hidden fillet formed. Sample with x-ray on anything above Class 1.
• Withdrawn JEDEC outline quoted in the library. MO-052 and MO-061 are no longer current, and a footprint traced from an old drawing may not match the part being bought.
• Coplanarity not checked on aged stock. J leads are mechanically tough but a lead lifted above the 0.10 mm envelope produces an open that no optical step will catch.
• Socket end-of-life ignored. The socket, not the IC, is often the part that becomes unbuyable first.

Frequently asked questions

What is a J-lead package?

A surface-mount package whose leads exit the body, bend down and curl back inward underneath it, forming a J in cross-section. PLCC uses J leads on four sides and SOJ uses them on two. JEDEC describes the small-outline J-lead package as a small-outline package with leads formed into a J configuration.

What is the difference between J-lead and gull-wing packages?

The lead direction. A gull wing bends outward so the foot sits beyond the package outline and the joint is fully visible. A J lead bends inward so the contact patch sits under the body. J-lead packages need less board area for the same body but cannot be inspected optically in the same way.

What is the pitch of a PLCC package?

1.27 mm, or 0.050 inch, on every registered PLCC outline. Both the square MS-018 and rectangular MS-016 families use it, and so does the SOJ family. Lead width is 0.66 mm to 0.81 mm and lead thickness 0.33 mm to 0.53 mm on the drawings checked here.

How do you inspect a J-lead solder joint?

Optically you can only judge the 0.4 mm to 0.6 mm of lead that projects beyond the body, plus wetting on the exposed land. The contact patch and most of the fillet are hidden, so Class 2 and Class 3 assemblies normally add x-ray, and qualification builds add cross-section sampling.

Is PLCC obsolete?

Not obsolete, but no longer a default. New designs use gull-wing or leadless packages for density and inspectability. PLCC is still the right answer where a device has to be socketed and field-replaceable. Watch socket availability rather than device availability when planning a long build.

Which JEDEC standard covers PLCC?

MS-018 for the square family and MS-016 for the rectangular family, both at 0.050 inch pitch. MO-047 also remains registered for the square plastic chip carrier. MO-052, which older references cite for rectangular PLCC, was replaced by MS-016.

What to do next

If you are inheriting a J-lead position, pull the manufacturer drawing for the exact part, confirm the MS-016 or MS-018 variation letter, and check that your land extends inward under the body far enough to cover the contact patch. Then decide the inspection method before the first build, because you cannot add it later from photographs.

If you are choosing the package, use a J-lead part only when the device must be socketed or when you are matching an existing board. For anything new and soldered down, a gull-wing or leadless package gives you a joint you can see, a lower profile and a supply chain that is not thinning.

Sources

JEDEC, Publication 95 microelectronic outlines (MO) index. https://www.jedec.org/sites/default/files/MOINDEX.pdf

JEDEC, Publication 95 microelectronic standards (MS) index. https://www.jedec.org/sites/default/files/MSINDEX_0.pdf

JEDEC dictionary, small-outline J-lead package (SOJ). https://www.jedec.org/standards-documents/dictionary/terms/small-outline-j-lead-package-soj

Renesas, package outline drawing N44.65, 44-lead PLCC, JEDEC MS-018AC issue A. https://www.renesas.com/en/document/psc/package-drawing-plcc-44pin-n4465

Renesas, package outline drawing N32.45×55, 32-lead PLCC, JEDEC MS-016AE issue A. https://www.renesas.com/en/document/psc/package-drawing-plcc-32pin-n3245x55

IPC, IPC-A-610H table of contents (clause 8.3.7 J leads, Table 8-7). https://www.electronics.org/TOC/IPC-A-610H-toc.pdf

S. Wolfangel, Optimizing thermo-mechanical reliability of components with flat gull wing leads, SMTA conference paper. https://www.electronics.org/system/files/technical_resource/E39&S01_01%20-%20Simon%20Wolfangel.pdf

Digi-Key product listing, 3M 8444-11B1-RK-TP 44-position PLCC socket (lifecycle and pricing checked 11 August 2026). https://www.digikey.com/en/products/detail/3m/8444-11B1-RK-TP/1026473

[INTERNAL LINK: gull-wing lead solder joint criteria -> SOIC and QFP land pattern and inspection guide]

[INTERNAL LINK: IPC-7351 land pattern density levels -> IPC-7351 naming and density level selection]

[INTERNAL LINK: PLCC socket selection -> IC socket types and when to use them]

[INTERNAL LINK: reading a JEDEC package outline drawing -> JEDEC MO and MS registered outlines explained]

[INTERNAL LINK: x-ray inspection of hidden solder joints -> BGA and BTC inspection methods]