Authored By:
Sunny Agarwal
ITW EAE - Camalot
Hopkinton, Massachusetts 01748
Summary
Today’s unique assembly challenges are comprised of complex PCB panelization, involving identical PCBs with a goal towards increased production capability, due to a reduced footprint of the Production Floor. Identical PCBs that are within the same panel, with uniform spacing in an array or carrier, need to be dispensed at the same time. All these high-mix challenges have gone mainstream and affects the real productivity and throughput. Existing manual dual head dispensing systems do not consider the rotational correction for the second head, which leads to yield loss. To eliminate the yield loss on second head, there is a mini XY drive system incorporated that provides fast and accurate dispensing to double the process capabilities over the same work area. Dynamic dual head dispensing uses a unique mini XY drive system on left head, mounted on a separate Z-axis, to dynamically control the position of the second head for accurately aligning to a second part, while synchronously dispensing both parts.
Machine vision system performs the substrate alignment for each identical PCBs that are individually placed in a carrier, which provides greater potential for variation in offset and skew. During synchronous dispensing for the second part with the DDH, all the kinematic adjustment is performed with calculated values, from the skew angle and scaling factor. This technique guarantees increased productivity whilst maintaining yields through unsurpassed accuracy. DDH also provides the same level of adjustment and rotational correction for all step and repeated PCB’s, flex circuits and panel designs. If product contains odd number of units then either of the head can be programmed for dispensing while the others can’t.
This paper examines proven methods to determine the dot/line positional accuracy along with mass flow rate for both heads during synchronous dispensing. This paper will also address the challenges faced, and how the rotational correction can achieve up to 2X higher dispense productivity then existing single/dual head dispensing systems.
Conclusions
Dual dynamic dispensing with the mini XY drive system has brought a new level of robustness to the high-volume manufacturing process. Furthermore, the offset distance between the multiple dispensing pumps is adjusted dynamically in XY direction to be the same as the offset distance between the multiple circuit distances to attain the same level of accuracy as the dispensing system. This way the multiple dispensing pumps can be utilized to increase throughput without any defect count coming from the left head mounted on the mini XY drive system.
With Cpk numbers greater than 1.33 for both dot and line positional accuracy at ±3 sigma capability indicates that mini XY drive mechanism does not have any adverse effect on the accuracy of the left head which in turn is close to the right head. Dual head “real time dispensing” with mini XY drive system has arrived offering greater degree of process control with skewed identical substrates adjacent to each other thus providing good product reliability during the production run. Also, less manufacturing floor space required with almost dual increase in productivity.
Initially Published in the SMTA Proceedings
|
