The packaging hierarchy is not fixed structure. It can be changed depending on the packaging technology itself, and the number of hierarchy levels tends to decrease. In LSI-package technology including package-to-board interconnections, there were two evolutionary changes. The first evolution was from PTH to SMT, and the second evolution was from "Peripheral connections" to "Area-array connections. " These evolutions have been caused by ICs integration and application products requirements. Now, the third evolution appears to be in progress, which is from SCP to MCP or SIP. Although SoC has many remarkable features, it has been not applied for many systems contrary to expectations, and its limitations or issues have become clear. SIP is the answer for above SoC's issues. MCP can be considered to be primitive SIP. The purpose of MCP is making up the technology gap between SMT and SoC to address the issues. The targets of SIP are mainly the next two items. (1) Overcoming the interconnection crisis of SoC. (2) Opening new application fields in electronics. In order to achieve those targets, several consortiums in the world are doing research and developing core technologies.

We introduce a new type of optical microconnector named "put-in microconnector-" using a planar microlens. The connector part is composed by a lens jack and fiber plug, where the lens jack is a hollow formed on a planar microlens surface, and the fiber plug is a protuberance formed on the core of an optical fiber. This concept can realize an alignment-free single mode fiber coupling. In this paper, we describe the structure and fabrication process, the optical coupling characteristics of the fabricated device, and finally, the basic analysis of optical coupling module. For the optical coupling characteristics, we measured the coupling loss and the return loss. The optical coupling loss of about 4 dB and the return loss of about 49 dB were obtained at wavelength of λ = 0.633 µm. Moreover, we have confirmed that the insertion loss of such a structure does not increase so much in comparison with that of the butt jointing. For the purpose of characterizing the optical property, the theoretical analysis was performed. We have made a software tool to estimate the optical coupling loss due to the position error. For this type of structure, the tolerance of about 15 µm for the distance between the laser and the planar microlens and 150 µm for the distance between the planar microlens and the optical fiber were estimated. Since the put-in microconnector does not require any precise alignment, it is appropriate for mass production.