There are two technical factors. The first is that higher temperature furnaces are required for iron smelting (1200C and up), compared to copper smelting (1100-1200C). In addition, the output from the iron smelting furnace is a solid spongy mass of iron and slag mixed together (called a bloom), and further processing is required. I discussed this in more detail in https://www.reddit.com/r/AskHistorians/comments/7ryt2v/why_was_there_a_widespread_bronze_age_before_the/

The other technical factor is that bronze is superior to iron in most ways. Bronze is of similar hardness, tough, and can be cast, and can be cold-forged which makes thin sheets easier to produce. It is also corrosion resistant. The advantage of iron is that iron ore is abundant, much more common than copper ore, and much, much more common than tin ore. Once there is a well-established iron industry, iron is much cheaper than bronze. Later, with the development of steel and techniques for hardening steel, steel can be greatly superior to bronze for many tasks. But before then, bronze is, mostly, superior. I discussed this in more detail in https://np.reddit.com/r/AskHistorians/comments/aexgpk/if_iron_is_really_better_than_bronze_in_every_way/

There are also social factors, as discussed by u/Antiquarianism in the first-linked question above, https://www.reddit.com/r/AskHistorians/comments/7ryt2v/why_was_there_a_widespread_bronze_age_before_the/