The SOJ-42 package is a 42-lead small-outline J-lead package on 1.27 mm pitch, 21 leads per side, almost always 400-mil width. It was the standard body for x16 DRAM in the 1990s and is obsolete today. Its JEDEC outline is MS-027, not the MO-061 number still printed in old datasheets — that registration was rescinded in June 1995.
Key takeaways
- Pitch is 1.27 mm; 21 pads per side put the first and last pad centres 25.40 mm apart.
- The 400-mil SOJ family moved from MO-061 to MS-027 (issue A, June 1995). Cite MS-027.
- A 400-mil SOJ land pattern uses 1.70 × 0.60 mm pads with the rows 9.40 mm apart, centre to centre.
- Cross-section dimensions carry across the 400-mil family; body length does not.
- Parts that used SOJ-42 were 1M × 16 DRAM, and shipped in 44-pin TSOP II as well — that is the migration path.
[IMAGE 1: dimensioned end view of a 400-mil SOJ with E, E1, E2 and A called out | alt: “SOJ-42 package dimensions showing body width, lead row spacing and overall lead span”]
What shipped in a SOJ-42 package
Three device families account for most SOJ-42 parts still turning up in repairs and legacy BOMs. All are 1M × 16 DRAM.
| Device | Manufacturer | Organization | Alternative package |
| IS41C16100 / IS41LV16100 | ISSI | 1M × 16 EDO DRAM, 5 V / 3.3 V | — |
| MT4C1M16C3 | Micron | 1M × 16 FPM DRAM | 44-pin TSOP II |
| AS4LC1M16E5 | Alliance Semiconductor | 1M × 16 EDO DRAM, 3 V | 400-mil 44/50-pin TSOP II |
Table 1. Device families offered in 42-pin SOJ, per manufacturer feature lists and distributor listings.
ISSI’s listing records the package as 0.400 inch, plastic, MS-027, SOJ-42, and the lifecycle as obsolete. A live footprint against a dead part number is the usual reason to search for this package.
SOJ-42 dimensions: the 400-mil cross-section
Every dimension except body length is shared across the 400-mil SOJ family. The values below come from Alliance Semiconductor’s AS7C31024B datasheet (v1.2, 24 March 2004).
| Symbol | What it measures | 400-mil SOJ |
| e | Lead pitch | 1.27 mm BSC |
| E | Plastic body width | 8.99 – 9.60 mm |
| E1 | Lead row dimension | 10.03 – 10.29 mm |
| E2 | Overall span across leads | 11.05 – 11.30 mm |
| A | Overall height | 3.35 – 3.71 mm |
| A1 | Standoff | 0.64 mm min |
| A2 | Body thickness | 2.67 – 2.92 mm |
| b | Formed lead width | 0.38 – 0.51 mm |
| c | Lead thickness | 0.18 – 0.33 mm |
| D | Body length | Scales with lead count — read from your own drawing |
Table 2. The 400-mil SOJ cross-section, from Alliance Semiconductor AS7C31024B v1.2. The drawing is inch-controlled; millimetre values are converted. Body length is not transferable between lead counts.
The 0.400 inch in the package name is E1, the lead row, not the plastic body. The body itself measures 8.99 – 9.60 mm while the leads reach 11.05 – 11.30 mm overall. Count lead positions, not leads, when measuring a sample: TopLine’s SOJ library records DRAM built with 20 leads on a 26-position body, so depopulated positions are normal here.
The JEDEC registration for a SOJ-42 is MS-027
The main index to JEDEC Publication 95, updated March 2026, settles which document applies.
| Document | Title | Issue and date |
| MS-027 | PDSO-J — the current .400″ SOJ family registration | A, June 1995 |
| MO-061 | Replaced by MS-027 | June 1995 |
| MS-023 | Plastic SOJ, .300″ wide body, .050″ pitch (R-PDSO-J/SOJ) | A, March 1995 |
| MO-199 | Low Profile SOJ (LSOJ) — registered pin counts include 42 | B, June 1999 |
| MO-200 | SOJ assembly, 2-high / 4-high stack | B, June 1999 |
| Design Guide 4.13 | Metric Small Outline J-Leaded Package (SOJ) | A, August 1996 |
| SPP-011 | J-lead dimensioning of lead contact points | January 1992 |
| CO-032 | Thin matrix tray for handling and shipping SOJ packages | A, April 1996 |
Table 3. JEDEC Publication 95 documents that govern a 42-lead SOJ, per the main index updated 03/26.
A datasheet citing MO-061 for a 400-mil SOJ is citing a rescinded registration, which matters when an audit asks for the controlling standard. Note also that 42 leads appear under LSOJ, so rule out a low-profile variant on your specific part.
SOJ-42 footprint and land pattern
No mainstream CAD library ships a SOJ-42. KiCad’s official library covers SOJ-36 at 400 mil, and that lead-row geometry transfers to any lead count in the family. Extending it to 21 pads per side gives the pattern below.
| Feature | Value | Basis |
| Pad count | 42, 21 per side | — |
| Pad size | 1.70 × 0.60 mm | KiCad SOJ-36 400-mil footprint |
| Pad pitch | 1.27 mm | KiCad SOJ-36 400-mil footprint |
| Row spacing, centre to centre | 9.40 mm | KiCad SOJ-36 400-mil footprint |
| Outer extent across rows | 11.10 mm | Derived: 9.40 + 1.70 |
| Inner gap between rows | 7.70 mm | Derived: 9.40 − 1.70 |
| First to last pad centre | 25.40 mm | Derived: 20 × 1.27 |
| Pad extent along the row | 26.00 mm | Derived: 25.40 + 0.60 |
| Courtyard width | 11.60 mm | KiCad SOJ-36 400-mil footprint |
Table 4. A 400-mil SOJ-42 land pattern, built from KiCad’s SOJ-36 400-mil lead-row geometry with 21 pads per side.
Check the outer extent against Table 2 before release. The 11.10 mm pad extent sits just inside the 11.05 – 11.30 mm lead span, as a J-lead footprint should: the pad wraps the outside of the curl, with no heel extension. Set courtyard length from your device’s body length, not the pad row.
[IMAGE 2: SOJ-42 land pattern with pad size, pitch and row spacing dimensioned | alt: “SOJ-42 package footprint with 1.70 by 0.60 mm pads on 9.40 mm rows”]
Sourcing and migration
Treat SOJ-42 as end-of-life. The ISSI part is marked obsolete, and unlike the 32- and 44-lead SRAM SOJ codes Alliance Memory still stocks, no manufacturer catalogues a new 42-lead SOJ device.
The migration is already documented by the original vendors: Micron paired its 42-pin SOJ with a 44-pin TSOP II, and Alliance paired its with 400-mil 44- and 50-pin TSOP II.
SOJ-42 design and sourcing mistakes
- Citing MO-061 as the controlling outline. It was replaced by MS-027 in June 1995.
- Transferring body length between lead counts. Only the cross-section carries across.
- Planning AOI-only inspection. Part of a J-lead joint is hidden under the body and needs X-ray for Class 3 work.
SOJ-42 package FAQ
What are SOJ-42 package dimensions?
For the 400-mil family: body width 8.99 – 9.60 mm, lead row 10.03 – 10.29 mm, overall lead span 11.05 – 11.30 mm, height 3.35 – 3.71 mm, standoff 0.64 mm minimum, pitch 1.27 mm. Body length varies with lead count and must come from your own drawing.
What is the SOJ-42 footprint?
42 pads of 1.70 × 0.60 mm on 1.27 mm pitch, 21 per side, with the rows 9.40 mm apart centre to centre. First to last pad centre is 25.40 mm, and the pattern spans 11.10 mm across the rows. Verify that span against your device’s lead dimension.
What JEDEC standard covers the SOJ-42 package?
MS-027, titled PDSO-J, issue A, June 1995. It replaced MO-061, the earlier .400 inch plastic SOJ family registration, which the JEDEC Publication 95 main index now lists as rescinded. A 42-lead low-profile variant also falls under MO-199, the LSOJ family registration.
Are SOJ-42 parts still available?
Not from current production. The 1M × 16 DRAM devices that used it are obsolete and remaining supply is broker stock. Where a redesign is possible, the 44-pin TSOP II option those same manufacturers offered alongside the SOJ is the documented alternative.
What to do with a SOJ-42 on your BOM
For a repair or a last-time build, pull the drawing for the exact device, take body length from it, and use Table 4 for everything else. For anything you can redesign, move to the 44-pin TSOP II variant the original vendor already qualified — the footprint work is the same either way, and only one of the two has a supply chain behind it.
