Package-on-Package
CPU on DRAM, stacked in one reflow.
Package-on-Package assembly for mobile, wearable and SiP designs where every square millimeter counts. Flux-dip jet, single-pass reflow, 3D X-ray per stack.
- BGA pitch
- 0.3 mm
- Stacks
- 3×
- X-ray
- 100%
- Reflow
- 1 pass
Process sequence
One reflow, every tier landed
Bottom-tier paste print → tier-2 flux dip → tier-3 flux dip → single reflow — no intermediate thermal cycles to stress the underfill.
Laser-cut stencil · bottom-tier pads only
0.4 mm pitch FCBGA, placed first
DRAM balls dipped in flux jet, not paste
Top-tier µBGA dipped and placed
Single profile cures entire stack · 100% 3D X-ray
Why choose PoP
When board area runs out, build up
PoP keeps interconnect between CPU and memory short — better signal integrity, lower power — while freeing up board area for sensors, RF and batteries.
- Phones & wearables
- AR / VR headsets
- IoT edge compute
- Drone flight controllers
- Smart watches
- Automotive infotainment
- Industrial AI modules
- Medical wearables
Capability
Published PoP capability
| Geometry | |
| Tiers | 2-tier · 3-tier (standard) |
|---|---|
| Min pitch (top tier) | 0.3 mm |
| Min pitch (bottom tier) | 0.4 mm |
| Min stack height | 1.2 mm typical · 0.9 mm ultra-thin |
| Max die size (top) | 15 × 15 mm |
| Process | |
| Flux method | DEK flux-dip jet · controlled depth |
| Reflow | 10-zone · N₂-optional profile |
| Underfill | Optional capillary or NCF |
| Inspection | |
| X-ray | 100% 3D X-ray · Nordson Dage Quadra 7 |
| AOI | Pre-reflow paste AOI + post-reflow optical |
| Cross-section | On sample lots per program |
| Board support | |
| Board thickness | 0.4 – 3.2 mm |
| Min board flatness | ≤ 0.75% warpage (IPC-TM-650 2.4.22) |
| Compliance | |
| Quality | IPC-A-610 Class 3 · J-STD-001 |
| Cert | ISO 9001 · IATF 16949 · ISO 13485 |
Frequently Asked Questions
Package-on-Package FAQ
01Can you do PoP on a 4-layer board?
Not recommended — PoP needs short BGA escape routing to work. For production we ask for ≥ 8 layers with HDI or stacked microvias under the AP site.
02How do you handle reworkability?
PoP is reworkable but difficult — we budget 3-4 hours per stack for rework with a localized thermal zone. We prefer to de-risk up-front with a signoff build & full X-ray.
03Do you underfill every stack?
Not by default. For consumer electronics we ship non-underfilled; for drop-sensitive products (wearables, automotive) we add capillary or NCF underfill as a spec option.
04What about warpage control?
PoP is the first assembly process to punish a warped board. We pre-screen incoming boards to ≤ 0.75% warpage per IPC-TM-650 2.4.22 and use dedicated support jigs during reflow.
Ready when you are
Send your Gerber & BOM — get a quote in 24 hours.
NDA available · Free DFM review · Senior engineer response.