Micro Section of a PTH - Eurocircuits

To check the quality of PTH after the galvanic process we measure on every production panel the Cu plating thickness of several holes.

On every production panel we include test coupons. From every production batch we select some coupons and make micro sections of the PTH to check the quality of the PTH in the final PCB.

Effects that we may spot but as Eurocircuits want to avoid in production are:

Voids

No more than 3 voids per hole in no more than 2% of the solder holes.
The total area of voids per hole must not exceed 5% of the area of the hole.
No voids at the pad-to-barrel interface.
No circumferential void in excess of 90° (circumferential crack).

Nodules

Acceptable on the condition that :

The hole wall exhibits an otherwise smooth an coherent structure. (A)
No sign of cracks around the nodule-area.(B)
The minimum Cu-thickness is fulfilled.

Cracks

Cracks are not acceptable before or after thermal stress, accept for barrel/Corner crack (D)(C) after thermal stress not extending the through plating.

Other typical cracks:

(E) Barrel crack – not permitted before or after terminal stress.
(F) Crack around nodule – not permitted before or after terminal stress.
(G) Crack in inner pad or inner Cu-layer – not permitted before or after terminal stress.
(H) Foil-crack – is permitted after thermal stress only on outer layers, provided it does not extend through plating.

Roughness

Permitted if not reducing plating thickness below min

Burrs

Cu burrs at the edge of the drilled hole must not have a burr height (g) of more than 50 % of the foil thickness and at most 25 micron. The burr height is understood as the dimension of the burr from foot to top (A), even if the burr is flattened (B).

Plating separation

Plating separation between laminate and hole wall is acceptable if extending over no more than 40 % of the PCB-thickness (t).
The separation can occur as :