Plated Through Hole Quality Factor 

IPC TR 579

The IPC-TR-579 spec is not very clear about the difference between Good and Superior

https://shop.ipc.org/general-electronics/standards/579-0-0-english

Quote: Section 2, Conclusions and Recommendations #13-15

13.  PTH quality is the principal influence on reliability.

14.  The task force found that an analytical PTH-Quality Index (see Section 7) can successfully quantify the PTH quality and its impact on PTH reliability.

15.  The copper plating process window narrows as the PTH aspect ratio increases. For example; high aspect-ratio PTHs (9:1) of marginal quality reach 1% failure hazard levels at about 75, 200 and 450cycles in respective use environments of 120, 80 and 6°C temperature excursions (based on the analytical model in Section 7).

Quote: Section 7

The PTH-quality index, KQ , is probably affected by a complex mixture of interacting PTH and PWB processing effects. These effects clearly can be separated into PTH hole quality effects (PWB construction layup, PWB lamination, PTH drilling, PTH smear removal) and PTH copper plating quality effects.

KQ can be considered a vendor/process rating index since it reflects the PTH manufacturing difficulties arising from smaller PTH diameters and larger PWB thicknesses as well as the ability of a particular vendor/process to deal with these difficulties.

The PTH-quality index KQ is incorporated in Equation 8 in a manner that KQ represents the PTH quality on an ascending scale of 0 to 10.

Quote: A number of trends and observations are evident from the data:

• PTH quality decreases more rapidly with decreasing PTH diameter for the lower rated vendors—this indicates a tendency towards mass-transport- limited plating for the lower rated vendors;

• For .030 and .060-thick PWBs, a number of samples did not fail in 400 MIL-T- CYCLES for any PTH diameter, while no .090-thick samples survived 400 such cycles for any PTH diameter. This might indicate a PWB thickness limitation for standard electrolytic plating due to mass-transport limitations and the need for extraordinary measures to assure adequate electrolyte exchange in the PTHs;

• The PTH-quality indices for the 10-mil-diameter PTHs show ranges of >7.0 to 6.3, >8.6 to 2.8 and 4.9 to 0 for the .030-, .060- and .090-thick PWBs, respectively—this clearly indicates that PTH manufacturing difficulties increase with increasing PWB thickness and decreasing PTH diameter;

• PTHs plated with electroless copper show PTH-quality index ranges for the 10-mil- diameter PTHs of >7.0, >8.6 to 8.0 and none (no samples submitted) for the .030-, .060- and .090- thick PWBs, respectively, while electroplated PTHs show index ranges of >7.0 to 6.3, 8.5 to 2.8 and 4.9 to 0.0.This indicates the greater ease of uniform electroless plating in high aspect-ratio PTHs;

• It appears that KQ ≥ 7.5 would indicate superior PTH quality, 7.5 >K Q ≥6.0 good PTH quality, 6.0 >KQ , ≥ 3.5 marginal PTH quality and K Q <3.5 poor PTH quality.

The PTH quality is a function of the PTH hole quality (smooth hole walls, fully cured B-stage layers not resin-rich) and PTH plating quality (uniform plating thickness without ‘‘dog-boning’’, high strength/high ductility throughout). For this analysis perfect PTH hole/plating quality has been assumed with deviations from this assumption reflected in values of KQ <10.

What are the properties of the copper deposits in PTH barrels? This is an open question. The answer depends on plating conditions and agitation level [12]. Given the paramount importance of the PTH hole/plating quality, it is clearly necessary that a method be developed that will produce testable samples with the same characteristics as the plated copper in a PTH barrel.

But what does it mean?

It is unclear how to determine the quality factor without some experimentation.

It is also PTH process and vendor specific.

One of my key takeaways is that the cross section of the test specimen should match your real PTH going to the field.

And your board manufacturing process should be audited on a regular basis to get the “Superior” quality.

Copyright Gil Sharon March 14, 2023. All rights reserved.