LOL. I thought you were asking me for evidence that the term does not appear until the end of the second century.
I see no point in laughing.
In any case, St. Ignatius never uses the term Trinity.
Non-use of the word doesn't mean non-portrayal of its theology.
I believe Tertullian was the first, though some would say the concept was first articulated by Valentius "The Father uncovers his bosom, which is the Holy Spirit, revealing his secret. His secret is his Son!" (Valentinus. Gospel of Truth. Verse 17. English translation by Patterson Brown). Both Tertullian and Valentinus were considered heretics. Valentinus is condemned in Irenaeus. Adversus Haeres. Book III, Chapter 3, Verse 4 and Tertullian articulated his views of the Trinity after he became a Montanist, which was also considered heretical.
See the above; it is why your opinion is wrong.
Tertullian was orthodox before his downfall, and it wasn't due to his Trinitarian theology but due to other things; he was Trinitarian in his orthodox years. Furthermore, Valentinus was heretical due to his Gnosticism. Since actual Trinitarianism declares the material nature of the Incarnation of God the Son, his concept wasn't the same, not to mention that the actual Greek used in the title is
natures; in actual Trinitarianism, the three Persons aren't different natures but the
same Nature.
Not to mention the fact that it is exceptionally dishonest to say "St. Ignatius never uses the term Trinity" and then bring up Valentinus.
And the first use of the word "Trinity" wasn't by Tertullian. It was by Theophilius, Patriarch of Antioch, who was around earlier.
And we find very Trinitarian writings in St. Ignatius in 110ce in his
Letter to the Magnesians and by St. Justin the Martyr a few decades later, in his
First Apology. Both of these predate Pheophilius, Tertullian, and, in terms of St. Ignatius, Valentinus (St. Justin the Martyr was very much Valentinus' contemporary; the likely shared the same birth year and the good Saint lived a mere ~5 years longer).