An FQFP package is a fine-pitch quad flat package: a plastic gull-wing QFP with lead pitch at or below 0.5 mm. The term is real but close to extinct on datasheets. No package outline registered in JEDEC Publication 95 carries FQFP in its title, and distributor stock under that name is thin. What you actually order is an LQFP or TQFP with the pitch stated.

Key takeaways

• FQFP is a descriptive family name, not an orderable package designation.
• JEDEC’s registered fine-pitch QFP outline is MS-029, issued August 1997. Cite that, or MS-026 for LQFP and TQFP.
• IPC-7351B splits its gull-wing land-pattern rules at 0.625 mm pitch. That is the practical fine-pitch line.
• At 0.4 mm pitch the worst-case gap between adjacent leads is around 0.09 mm once the dambar allowance is counted.
• Body thickness and volume, not pin count, set the reflow classification temperature.

What FQFP stands for

FQFP stands for fine-pitch quad flat package: a plastic surface-mount package with gull-wing leads on all four sides and a lead pitch of 0.5 mm or finer. It is a descriptive family name rather than a registered outline. Devices are ordered as LQFP or TQFP with the pitch called out.

[IMAGE 1: top and side view of a 176-lead LQFP at 0.4 mm pitch with pitch, lead width and standoff dimensioned | alt: “FQFP package dimensions on a 176-lead fine-pitch quad flat package at 0.4 mm pitch”]

Where the acronym is official, and where it is not

The JEDEC Publication 95 master index settles it. Searching the registry for FQFP returns exactly one document: CS-004, “FQFP/MQFP Thin Matrix Tray for Handling and Shipping,” Issue B, May 1996. The acronym survives in a shipping-tray standard, not in a package outline.

One manufacturer did use it as a package code. Infineon’s ADM5120P network processor shipped in a case listed as P-FQFP-208, expanded by distributors as Plastic Fine Pitch Quad Flat Package. That part is now marked obsolete and end-of-life.

The JEDEC outlines to cite instead

Put one of these on the drawing, not “FQFP.”

Outline	Registered title	Issue	Date
MS-022	Metric Plastic Quad Flat Pack Family, 1.0, 0.8, 0.65 pitch	B	December 1996
MS-026	Low/Thin Profile Plastic Quad Flat Package, 2.00 mm footprint, optional heat slug	D	January 2001
MS-029	Fine Pitch Plastic Quad Flat Package Outline, 2.6 mm footprint	A	August 1997
MO-108	Metric Plastic Quad Flat Pack Family, 1.0, 0.8, 0.65 pitch (PQFP-G/MQFP)	C	August 1996
MO-112	Metric Plastic Quad Flatpack Family, 3.9 mm footprint	B	September 1995
MO-292	Very Thin Fine Pitch Plastic Quad Flat Package, 2.00 mm footprint	C	April 2010

MS-029 replaced MO-143 in June 1997, and MS-026 replaced MO-136. A real drawing shows how this lands in practice: Analog Devices’ 64-lead LQFP, package code ST-64-2, is marked compliant to JEDEC MS-026-BCD, with 0.50 mm BSC lead pitch, a 10.00 mm square body, and a 12.00 mm square lead span.

Where fine pitch actually begins

The top-ranking pages say “0.5 mm or less” without a source. IPC gives a sharper line. IPC-7351B publishes separate land-pattern tables for gull-wing and flat ribbon L leads above and below 0.625 mm pitch, and the tables differ in the side solder-joint goal. Below 0.625 mm the side fillet target changes because there is no longer room for it.

Manufacturer nomenclature agrees. Cirrus Logic defines TQFP as a 0.80 mm to under 1.40 mm thick body with 0.50 or 0.40 mm lead pitch, LQFP as a 1.40 mm to 2.0 mm body at the same pitches, and MQFP as a 2.10 mm to 3.50 mm body at 0.80, 0.65 or 0.50 mm. So 0.65 mm is the boundary, and 0.50 mm and 0.40 mm are the fine-pitch working set.

Fine-pitch QFPs you can actually order

Numbers below are from the Cirrus Logic Package Information Guide v5.0, June 2001. Thermal figures were measured in still air at 50% PCB metallization, with TA = 70 °C and TJ = 125 °C.

Package	Body	Pitch	Max lead width	θJA	θJC
144-pin LQFP	20 × 20 × 1.40 mm	0.50 mm	0.27 mm	65 °C/W	10 °C/W
176-pin LQFP	24 × 24 × 1.40 mm	0.50 mm	0.27 mm	40 °C/W	10–15 °C/W
208-pin LQFP	28 × 28 × 1.40 mm	0.50 mm	0.27 mm	39 °C/W	13 °C/W
120-pin LQFP	14 × 14 × 1.40 mm	0.40 mm	0.21 mm	55 °C/W	9 °C/W
176-pin LQFP	20 × 20 × 1.40 mm	0.40 mm	0.23 mm	63 °C/W	10 °C/W
256-pin LQFP	28 × 28 × 2.00 mm	0.40 mm	0.23 mm	25 °C/W	7 °C/W

Two patterns worth reading off that table. Dropping from 0.50 mm to 0.40 mm buys pin count in the same body — 14 × 14 mm carries 120 leads at 0.40 mm where it would carry fewer at 0.50 mm. And θJA improves with body size, not with pitch: the 28 × 28 mm parts are the good thermal performers.

Package parasitics are modest by modern standards but not negligible. The 176-lead 0.40 mm LQFP is specified at 2.0–7.0 pF, 7–10 nH and under 100 mΩ.

The lead-gap margin nobody publishes

This is the calculation that decides whether your assembly house can build the board.

[IMAGE 2: close-up of adjacent gull-wing leads with pitch, lead width and dambar protrusion called out | alt: “Adjacent lead gap on a fine-pitch quad flat package showing dambar protrusion allowance”]

Start with a verified 0.50 mm part. The ADI ST-64-2 LQFP specifies lead width of 0.17 mm minimum, 0.22 mm nominal and 0.27 mm maximum. At nominal width the gap between adjacent leads is 0.50 − 0.22 = 0.28 mm. At maximum width it is 0.23 mm.

Then subtract what the drawing excludes. Manufacturer package notes are explicit: the lead width with plating does not include a total allowable dambar protrusion of 0.08 mm at maximum material condition. Counting that allowance once between the pair, the worst case at 0.50 mm pitch is 0.50 − 0.27 − 0.08 = 0.15 mm.

Now run the same arithmetic at 0.40 mm pitch with a 0.23 mm maximum lead width: 0.40 − 0.23 − 0.08 = 0.09 mm.

Pitch	Max lead width	Gap at max width	Gap after 0.08 mm dambar allowance
0.50 mm	0.27 mm	0.23 mm	0.15 mm
0.40 mm	0.23 mm	0.17 mm	0.09 mm

Ninety micrometres is the margin your stencil, paste and placement accuracy have to live inside. That number, not the pin count, is what a contract manufacturer will ask about first.

Coplanarity, bent leads and the migration threshold

Coplanarity is the distance between the seating plane and the lead tip; a bent lead is the lateral distance between the shoulder, where the lead meets the body, and the lead tip. Both are inspected, and both are why fine-pitch QFP yields fall. The ADI LQFP-64 drawing specifies 0.08 mm coplanarity.

There is a documented threshold for giving up on leads. Cirrus Logic states that plastic BGA becomes the preferred package when lead count exceeds 208 or QFP lead pitch drops below 0.50 mm, because coplanarity and bent-lead problems are a major yield loss in high-volume assembly. Grid arrays also give a slightly smaller footprint at equal lead count and better thermal and electrical performance.

The historical ceiling shows how hard the format was pushed. Intel developed a 296-lead thin plastic QFP at 0.4 mm pitch in a 32 × 32 mm body, 2.0 mm thick, with 0.25 mm maximum standoff, using tape automated bonding to the leadframe because wire-bond interconnect had run out of room.

Land pattern, stencil and reflow

IPC-7351B supplies three land-pattern geometries per device family: maximum protrusion (Density Level A), median (Level B) and minimum (Level C), and advises product qualification testing before adopting the minimum variation. For a fine-pitch QFP, Level C buys routing space and costs process window. Qualify it or stay at Level B. The sectional standard for this lead form is IPC-7355, equivalent to IEC 61188-5-5, covering gull-wing leads on four sides.

Reflow is set by geometry, not by lead count. J-STD-020 classification temperatures for lead-free process depend on body thickness and package volume:

Body thickness	Volume < 350 mm³	350–2000 mm³	> 2000 mm³
< 1.6 mm	260 °C	260 °C	260 °C
1.6–2.5 mm	260 °C	250 °C	245 °C
> 2.5 mm	250 °C	245 °C	245 °C

Apply it to the table above. A 20 × 20 × 1.40 mm LQFP is under 1.6 mm thick, so it classifies at 260 °C. The 28 × 28 × 2.00 mm LQFP-256 sits in the 1.6–2.5 mm band at roughly 1,570 mm³, which drops it to 250 °C. Same family, same pitch, different ceiling.

Customer peak reflow temperature typically runs 235–250 °C and must stay below the classification temperature; ramp rate from liquidus to peak must not exceed 3 °C/s, cool-down must not exceed 6 °C/s, and time from 25 °C to peak should stay under 8 minutes. On floor life, MSL 3 allows 168 hours at 30 °C and 60% RH, which is the rating most large plastic QFPs carry.

[IMAGE 3: reflow profile with liquidus, classification temperature and peak marked | alt: “J-STD-020 classification reflow profile applied to a fine-pitch quad flat package”]

Five mistakes that cause returns

1. Searching distributor stock for “FQFP.” The field barely exists. Filter on package family and lead pitch instead.
2. Reusing a 0.65 mm land pattern at 0.50 mm. The IPC tables change at 0.625 mm; the footprint has to change with them.
3. Ignoring the dambar allowance. Designing to nominal lead width overstates your bridging margin by roughly a third at 0.40 mm pitch.
4. Setting one reflow peak for the whole board. Classification temperature varies with body thickness and volume across parts in the same family.
5. Adopting Density Level C without qualification. IPC says qualify first, and fine pitch is where that advice earns its keep.

FQFP FAQ

What does FQFP stand for?

FQFP stands for fine-pitch quad flat package, a plastic surface-mount package with gull-wing leads on all four sides at 0.5 mm pitch or finer. It is a descriptive category rather than a registered outline, so devices are ordered under a specific designation such as LQFP or TQFP with the pitch stated.

Is FQFP the same as TQFP or LQFP?

Not exactly. FQFP describes pitch; TQFP and LQFP describe body thickness. A TQFP body runs from 0.80 mm to under 1.40 mm and an LQFP from 1.40 mm to 2.0 mm, and both are offered at 0.50 mm and 0.40 mm pitch. So most modern TQFPs and LQFPs are fine pitch, but the terms are not interchangeable.

What lead pitch counts as fine pitch?

In practice, 0.5 mm and below. IPC-7351B draws its line at 0.625 mm, publishing separate land-pattern tables for gull-wing leads above and below that figure, with a different side solder-joint goal below it. That makes 0.65 mm the last coarse pitch and 0.50 mm the first fine one.

What is the finest lead pitch available in a QFP?

Volume production tops out at 0.4 mm. Below that, the gap between adjacent leads falls under 0.1 mm once dambar protrusion is counted, and handling damage dominates yield. Manufacturers have built prototypes finer, but the industry moved to grid arrays rather than pushing peripheral leads further.

Why do designers move from fine-pitch QFP to BGA?

Coplanarity and bent leads. Both scale badly with lead count and pitch, and both are inspected before assembly. Package vendors have long advised switching to plastic BGA above 208 leads or below 0.50 mm pitch, where grid arrays also give a smaller footprint and better thermal and electrical behaviour at equal I/O.

What to do next

Treat FQFP as a reading aid, not a purchasing term. When you see it in a legacy BOM or a glossary, resolve it to a real designation: pull the manufacturer package drawing, read the JEDEC outline and variation it cites, and record the pitch, maximum lead width and coplanarity from that drawing rather than a library default. Then run the gap arithmetic before you commit — if it lands near 0.09 mm, talk to your assembly house before you route the board, and if the design also crosses 208 leads, price a BGA alternative in the same review.

Internal links

• [INTERNAL LINK: LQFP vs TQFP → body thickness, pitch and footprint interchangeability]
• [INTERNAL LINK: JEDEC package outline numbering → how to read MS and MO designations]
• [INTERNAL LINK: IPC-7351B land pattern density levels → when to use Level A, B or C]
• [INTERNAL LINK: MSL and J-STD-020 → floor life, baking and reflow classification]
• [INTERNAL LINK: fine-pitch BGA vs QFP → choosing between peripheral leads and grid arrays]

Sources

• JEDEC, Master Index for JEDEC Publication No. 95: https://www.jedec.org/sites/default/files/Master.pdf
• Analog Devices, 64-Lead LQFP (ST-64-2), JEDEC MS-026-BCD: https://www.analog.com/media/en/package-pcb-resources/package/pkg_pdf/lqfpst/st_64_2.pdf
• Cirrus Logic, Package Information Guide v5.0: https://d3uzseaevmutz1.cloudfront.net/pubs/misc/PackageGuide5.pdf
• Texas Instruments, SPRABY1A, MSL Ratings and Reflow Profiles: https://www.ti.com/lit/an/spraby1a/spraby1a.pdf
• IPC-7351B naming convention and IPC-735x / IEC 61188-5 mapping: https://cxem.net/comp/files/comp149_Footprint-Naming-Convention_-Surface-Mount-Components.pdf
• IEEE, 296 lead fine pitch (0.4 mm) thin plastic QFP package with TAB interconnect: https://ieeexplore.ieee.org/document/367652