This paper concerns resource planning in a VLSI assembly facility. The facility can process more than 100 sorts of WIPs (Works-In-Process) simultaneously. Specifically it performs product-mix production. An old resource estimation system, which gave a good estimation for a memory VLSI production facility, went wrong for an assembly facility. To adjust the estimation of required machinery resources of the assembly facility, a new parameter--the tuning value for the service time--is introduced. The tuning value expresses the reduction in machine utilization in the processing steps due to the product-mix. The value is empirically determined and the machinery resources can be estimated in good accuracy. Also the waiting time for processing in the incoming buffer is successfully considered in the estimation of turnaround time. However the tuning value is not enough in estimating human resources. A novel algorithm to estimate the resources for machine adjustments is proposed. The algorithm is based on a periodic assignment of multiple sorts of WIPs in a single machine, where the adjustments of machines for the product-mix are considered. The adjustments are additional operator's jobs in the product-mix. It estimates the operator request rate and machine utilization rate when multiple sorts of WIPs with different arrival rates are processed in a single machine. Finally, this resource estimation system considers the operator allocated not only to the preprocessing and postprocessing but also to the adjustments of machines for the product-mix. The estimated machinery, human resources, and turnaround time were evaluated in a real facility, and the proposed method is confirmed to be applicable in the weekly or monthly resource planning for the facility.