How to choose an open-cavity IC package and matching lid
An open-cavity (air-cavity) package is a finished package body with an empty cavity: you attach your own die, wire-bond it to the bond fingers and close the cavity with a lid. It is the quickest way to put MPW dies, sensors and engineering samples into a standard footprint that fits an existing socket or PCB.
This tutorial walks through the decisions in the order an assembly engineer makes them: die size, I/O count, pitch, bond fingers, plating, then the lid and how it is sealed. Every dimension below is taken from the manufacturer catalogue for parts listed on MST Store (made by Shanghai Xintaowei New Materials); always confirm against the drawing for your exact part number.
Step 1: Size the cavity from the die
Start from the die outline, not the package. The die must fit the die-attach area with room left for die-attach fillet and for the bond wires to leave the die edge. For the plastic air-cavity QFN family the catalogue gives a square die-attach area for each body size; the standard cavity depth is 0.65 mm, so check that the die thickness plus die-attach bond line plus wire loop height stays below the cavity depth and the lid.
If the die is close to the limit, move up one body size: the bond fingers move outward with the body, which also keeps wires shorter relative to the die.
| Body size | Max. die-attach area | Example part numbers on MST Store |
|---|---|---|
| 3 × 3 mm | 1.36 × 1.36 mm | ALNP-8-3-6.5, ALNP-12-3-5, ALNP-16-3-5 |
| 4 × 4 mm | 2.30 × 2.30 mm | ALNP-12-4-6.5, ALNP-16-4-6.5, ALNP-20-4-5, ALNP-24-4-5, ALNP-28-4-4 |
| 5 × 5 mm | 3.30 × 3.30 mm | ALNP-28-5-5, ALNP-32-5-5, ALNP-32-5-5H, ALNP-40-5-4 |
| 6 × 6 mm | 4.24 × 4.24 mm | ALNP-36-6-5, ALNP-40-6-5H, ALNP-40-6-5F |
| 7 × 7 mm | 5.20 × 5.20 mm | ALNP-24-7-10, ALNP-44-7-5, ALNP-48-7-5, ALNP-48-7-5H |
| 8 × 8 mm | 6.04 × 6.04 mm | ALNP-32-8-8, ALNP-56-8-5H |
| 9 × 9 mm | 6.90 × 6.90 mm | ALNP-44-9-6.5, ALNP-64-9-5H |
| 10 × 10 mm | 7.80 × 7.80 mm | ALNP-72-10-5, ALNP-88-10-4, ALNP-96-10-4 |
| 12 × 12 mm | 9.00 × 9.00 mm | ALNP-100-12-4H |
Part numbers read ALNP-<lead count>-<body mm>-<pitch>: the last field is the lead pitch in tenths of a millimetre (5 = 0.5 mm, 4 = 0.4 mm, 6.5 = 0.65 mm, 8 = 0.8 mm, 10 = 1.0 mm). Suffix letters mark variants of the same outline, for example ALNP-48-7-5H is 1.45 mm thick against 0.85 mm for ALNP-48-7-5; check the drawing.
Step 2: Choose the package type from the I/O count
Peripheral packages (QFN, QFP) route every signal to the outer edge, so the I/O count is limited by the perimeter and the pitch. Area-array packages (BGA, LGA) use the whole underside and suit higher I/O counts in a smaller footprint, at the cost of a board that can route an array.
- Up to about 100 I/O: plastic air-cavity QFN (8 to 100 leads listed) or HTCC ceramic QFN when hermeticity matters.
- Around 144 I/O with leads you can probe: ceramic quad flat pack, for example CQFP144-01 (19 × 19 mm) or ALNC-144-20-5 (20 × 20 mm).
- 256 to 512 I/O: cavity BGA, for example BGA1313-256BALLS (13 × 13 mm) or BGA2020-512BALLS (20 × 20 mm).
- LGA (land grid array) is the same area-array idea without solder balls, used mainly with sockets. No open-cavity LGA part is listed on MST Store at present; ask an engineer if your test plan needs one.
Size comparison: open-cavity packages listed on MST Store
| Part number | Type | Body | I/O | Pitch | Die size / die-attach area |
|---|---|---|---|---|---|
| ALNP-16-3-5 | Plastic air-cavity QFN (LCP) | 3 × 3 mm | 16 | 0.5 mm | 1.36 × 1.36 mm |
| ALNP-32-5-5 | Plastic air-cavity QFN (LCP) | 5 × 5 mm | 32 | 0.5 mm | 3.30 × 3.30 mm |
| ALNP-48-7-5 | Plastic air-cavity QFN (LCP), 0.85 mm thick | 7 × 7 mm | 48 | 0.5 mm | 5.20 × 5.20 mm |
| ALNC-48-7-5C | HTCC ceramic QFN, 0.8 mm thick, 0.5 mm cavity | 7 × 7 mm | 48 | 0.5 mm | 5 × 5 mm |
| ALNP-100-12-4H | Plastic air-cavity QFN (LCP) | 12 × 12 mm | 100 | 0.4 mm | 9.00 × 9.00 mm |
| CQFP144-01 | Ceramic QFP, 1.5 mm cavity | 19 × 19 mm | 144 | 0.5 mm | 12 × 12 mm |
| ALNC-144-20-5 | Ceramic QFP | 20 × 20 mm | 144 | 0.5 mm | 16 × 16 mm |
| BGA1313-256BALLS | Cavity BGA, 16 × 16 full array, 0.45 mm balls | 13 × 13 mm | 256 | 0.7 mm | 8 × 8 mm |
| BGA2020-512BALLS | Cavity BGA | 20 × 20 mm | 512 | 0.7 mm | 16 × 16 mm |
Only part numbers listed on MST Store are shown. Die size is the largest die the manufacturer lists for that body; confirm on the drawing.
Step 3: Match the pitch to your socket or board
The lead or ball pitch decides which test socket and PCB footprint you can use. The QFN outlines follow JEDEC MO-220, so a standard QFN socket for the same body, lead count and pitch should fit; confirm the exposed-pad size if your socket has a center ground contact. Finer pitch (0.4 mm) packs more leads on the same body but needs a finer-pitch socket and tighter PCB rules than 0.5 mm or 0.65 mm.
Step 4: Check bond-finger pitch and plating
- Bond-finger pitch limits your wire-bonding tool and wire diameter. For example, the BGA1313-256BALLS catalogue gives a bond-finger pitch of about 0.13 mm; ask for the bond-finger drawing before you lay out bond pads on a new die.
- ALNP-48-7-5 uses a Cu194 copper lead frame with nickel-gold plating; BGA1313-256BALLS uses a NiPdAu finish. Both finishes accept gold-wire bonding; confirm aluminium-wire or copper-wire compatibility with the manufacturer.
- Respect the process limits on the datasheet. For ALNP-48-7-5 the catalogue gives a die-attach cure up to 200 °C and wire bonding up to 100 °C, because the body is LCP plastic. Use ceramic when your die attach needs a higher temperature.
Step 5: Choose the lid and how it is sealed
The lid choice follows from the package and whether you need a hermetic seal. Adhesive-sealed lids are quick and need only a hot plate or oven; they are not hermetic to military-grade leak rates. A gold-tin (Au80Sn20) soldered metal lid on a ceramic package gives a hermetic seal; gold-tin is a eutectic alloy that melts at 280 °C. Hermeticity is normally checked with fine and gross leak tests such as MIL-STD-883 Test Method 1014.
| Lid | Material and seal | Size | Fits |
|---|---|---|---|
| PCLID0303 to PCLID1010 | Black alumina ceramic, 0.38 mm thick, pre-applied B-stage epoxy (8006NS), adhesive height 0.1 mm | Package outline minus 0.1 mm per side, for 3 × 3 to 10 × 10 mm bodies | Plastic air-cavity QFN of the same body size |
| PCLID1212 | Black alumina ceramic, B-stage epoxy | 11.85 × 11.85 mm | 12 × 12 mm plastic air-cavity QFN |
| QFN77LIDKAU | Kovar, Ni ≥ 3 µm / Au ≥ 1.3 µm plating, Au80Sn20 solder ring (inner 6.15 mm) | 6.90 × 6.90 mm, 0.25 mm (0.3 mm with solder) | 7 × 7 mm ceramic QFN such as ALNC-48-7-5C |
| Matching cap for BGA1313-256BALLS | LCP lid with 3 mm internal cavity, B-stage epoxy seal | 12.8 × 12.8 mm | BGA1313-256BALLS |
Manufacturer reference for the B-stage adhesive: cure about 30 minutes at 175 °C; store lids at −10 °C and use within 6 months. Confirm the cure profile against your die-attach and wire-bond limits.
Checklist before you order
- Die X × Y × thickness, pad count and a non-confidential bond-pad outline.
- Target package type, body size, lead or ball count and pitch.
- Highest temperature in die attach, wire bond and lid seal.
- Hermetic or non-hermetic; lid material and seal method.
- Socket or PCB footprint you will use, and quantity for packages and lids.
Frequently asked questions
How much larger than the die should the cavity be?
Use the die-attach area on the package drawing as the hard limit and leave room for the die-attach fillet and wire exit. If the die nearly fills the listed area, choose the next body size up.
Is a plastic air-cavity QFN hermetic?
No. The manufacturer states that plastic air-cavity packages with adhesive lids are not hermetic to military grade. Use an HTCC ceramic package with a gold-tin soldered metal lid when you need a hermetic seal.
Which lid goes with a plastic air-cavity QFN?
The black alumina PCLID lid of the same body size, for example PCLID0707 for a 7 × 7 mm body. It comes with a pre-applied B-stage epoxy that cures in about 30 minutes at 175 °C.
Can I use a standard QFN test socket?
Usually yes. The plastic air-cavity QFN outlines follow JEDEC MO-220, so a socket for the same body, lead count and pitch should fit. Confirm package thickness and exposed-pad size with the socket maker.
When should I choose a cavity BGA instead of a QFN?
When you need more I/O than a QFN perimeter allows. The cavity BGAs listed offer 256 balls on 13 × 13 mm and 512 balls on 20 × 20 mm, both at 0.7 mm pitch.
Ask an engineer
Send your die size, pad count, target pitch and whether you need a hermetic seal. MST, as distributor, checks the drawings with the manufacturer and quotes a matching package and lid.
Ask an engineerRelated pages
Sources
- Shanghai Xintaowei New Materials (ALN) product catalogue
- JEDEC MO-220 (QFN package outlines)
- MIL-STD-883 Test Method 1014 (seal / leak test)
Values are taken from the manufacturer documents above, checked 2026-10-24. Specifications can change; confirm against the current datasheet before ordering. MST is a distributor; products are made by the manufacturers named.