PTP Aluminium Foil Pinholes: Causes, Detection and What to Specify
2026-11-03
Why pinholes matter more than nominal thickness
A moisture-sensitive tablet fails on the shelf, not in the gauge report. PTP aluminium foil is specified in micrometres, but moisture ingress through a blister usually begins at a discrete defect rather than through the full surface. A single pinhole in the cavity area can pass enough water vapour over a two-year shelf life to change dissolution behaviour or appearance.
That is why gauge and pinhole count are separate specification items. A foil can meet its thickness tolerance and still carry pinholes from the rolling mill, from slitting and handling, or from the forming and sealing operation on your line.
Where pinholes come from
Rolling. Thin foil is rolled in multiple passes. Inclusions, scratches from work rolls and edge damage can create micro-perforations that survive downstream processing. Hard-rolled tempers behave differently from soft tempers, and the difference shows up in handling rather than in the datasheet.
Slitting and rewinding. Web tension, telescoping and edge contact during slitting can introduce mechanical damage. This is one of the reasons roll handling instructions belong in the specification file.
Printing and lacquering. Curing and drying steps stress the web. A print register that requires high tension increases the risk of micro-cracks in the aluminium layer.
Forming and sealing. On a blister line, the foil is pushed into the cavity and sealed under pressure and heat. Tool condition, seal pressure and plate flatness all affect whether a foil that arrived intact leaves the line intact.
Handling at the filler. Manual reel changes, drops and improvised storage are common causes that never appear in incoming inspection records.
How pinholes are detected
| Method | Where it fits | What it tells you |
|---|---|---|
| Light transmission on a light table | Incoming inspection, laboratory | Presence and location of through-defects in a sample area |
| Dye penetration | Laboratory, investigation | Confirms whether a visible mark is a through-hole |
| Online vision inspection | Running blister line | Detects defects in the sealed cavity area at line speed |
| Helium or pressure decay leak testing | Pack-level validation | Whether a finished blister leaks as a system |
| Stability and moisture uptake data | Product level | Whether defects that pass inspection still matter over shelf life |
No single method covers everything. Incoming inspection catches material defects; pack-level leak testing catches sealing problems; stability data tells you whether the acceptance limit is right for the product.
Specification points worth fixing
1. State the acceptance limit per unit area. A pinhole count without an area basis cannot be inspected against. 2. Define the sampling plan. How many metres per reel, from which positions, and what happens to a failed reel. 3. Agree the detection method. Light table, dye penetration or vision inspection produce different results on the same foil. 4. Fix the temper and surface treatment. Both influence how the foil behaves through printing, forming and sealing. 5. Include handling and storage conditions. Roll handling instructions are part of the defect story, not an administrative note. 6. Validate the limit against the product. The right limit depends on the moisture sensitivity of what goes inside the cavity.
Documentation to keep in the file
- Foil datasheet with gauge, temper and tolerance
- Pinhole acceptance limit with the inspection method stated
- Certificate of analysis per batch, including the inspection result
- Seal and peel validation with the nominated cavity film
- Stability data supporting the chosen barrier position
- Handling and storage instructions for reels
Where the material sits in the pack
PTP foil rarely performs alone. [PTP aluminium foil](/products/ptp-aluminum-foil) is specified together with the cavity film, and for moisture-critical products the pair may be replaced by [cold-forming aluminium without PVC](/products/cold-forming-aluminum-without-pvc), which forms a deeper pocket from a laminate. How the two approaches compare for tropical markets is covered in our technical articles, and material selection by market is summarised under industries we serve.
Working through a pinhole complaint
Start with the location: cavity area, seal area or flange. Cavity defects usually point to the foil; seal-area defects usually point to the line. Then compare incoming inspection records with the batch that failed, and check whether handling changed between the two. If the pattern repeats across batches, the acceptance limit or the detection method is usually the item to revisit rather than the supplier alone. Send the batch record, a sample and your line parameters through the contact form and our engineers will review the foil and the sealing set-up together.
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