It could possibly have been a typographic error: "Losinkrate" instead of "Lowinkrate", given that "s" and "w" are neighbours on both QWERTY and QWERTZ keyboards.

"The Direct Copper Bonding Substrate (DCB, also knows as DBC) is [used] for power electronic modules in [various] applications." ... "DCBs consist of a ceramic substrate [...] serving as an insulating layer, and copper connections to ensure the electrical conductivity [...]." ... Advantages include: "Low ink rate and high level of quality consistency" & "Low contamination with metal or ceramic particles"
https://www.heraeus.com/en/het/products_and_solutions_het/me...
https://www.heraeus.com/en/het/products_and_solutions_het/me...

"This new high quality paper is produced from white recycled pulp [...]. The [...] de-inking mill only recycles top quality waste paper such as office, archival and copy paper with a low ink rate, to ensure the highest quality of recycled pulp."
https://purelypaper.co.uk/Olin-70-Recycled-Paper-High-White-...

I can imagine that an AOI (automated optical inspection) unit could be well-suited to detecting ink levels on either a Direct Copper Bonding Substrate or a waste/recycled paper stream.
I can also envisage the ink (coverage/contamination) rate being measured as a percentage.

I cannot find "Lowinkrate" used anywhere, but — as others have remarked — it may have been an ad hoc coinage.

As others have further remarked, there would be more chance to correctly guess the meaning if more context were provided about the source text.