|Application:||Bonding vertical-cavity surface-emitting lasers (VCSELS) using gold/tin preforms|
|Equipment:||Model 410 Flip Chip Die Bonder; Model 860 Omni Bonder|
|Process:||Vertical cavity surface emitting lasers (VCSEL) are frequently mounted on T.O. headers with the emitting point of the laser centered in the diameter as a locator. The critical alignment is the laser is mounted using the header diameter as a locator. The critical alignment is the laser emission point to the lens. Other package types are also used, but the technique is essentially the same.
The laser die in this application are usually mounted with gold tin eutectic bonds using preforms as a source of bonding material. Conductive epoxy is also used (see: “Bonding VCSEL’s using conductive epoxy”).
In the case of eutectic bonds the header is firmly held and preheated to approximately 150°C.. A preform is placed on the header at the bond site, the laser die is aligned, the header is heated to melt the preform (approx. 325°C.), the die is heated (approx. 200°C.) and placed in the melt, scrubbed (optional), and then cooled. The bond load should be controlled (10-50 grams) to avoid die damage or stress.
|Machine Discussion:||A bonding system capable of performing this application needs the following features. A holder is required to present the diode and preform parts for pick-up. VCSEL’s are presented in a gel pack or waffle pack. Preforms are usually presented on a mirror or in a waffle pack.
The most common tool for picking and placing VCSEL’s is a flat faced pick-up tool. A four-sided collet can also be used. This tool only touches the edge and captures the diode if scrub is to be used. The die tool usually has a heater capable of 250°C. A flat faced unheated tool is needed to pick-up the preform and place it on the header.
Alignment of the VCSEL to the header requires a means to locate the emission point and mark or remember that location for future reference. The pick-up tool is going to block a direct view of the emission point and the perimeter of the die in reference to the diameter of the header by locating that diameter and centering the earlier marked reference point.
The placement of the die onto the header requires an accurately controlled bond load (20 to 50 gram range) to protect the fragile die and give repeatable bonds. The scrub mechanism, if used, must move precisely back and forth and return to the starting point within a few microns.
A stage that holds the header firmly by vacuum or mechanical clamping is needed. Clamping is suggested when scrub is used. The stage needs a heating system that can cycle through the temperatures required (150° – 325°C). Rapid heating and cooling are helpful in accommodating throughput.
|Machine Features:||The Model 410 Flip Chip Die Bonder and the Model 860 Omni Bonder have the following features which make them excellent systems for performing this application.
These bonders come equipped with a die tray holder that holds waffle packs for die and preform presentation. Gel packs are not compatible with heated bonding tools; an upcoming feature for the Model 860 is an alignment station that eliminates this problem. A die can be picked from a gel pack using the preform tool and placed on the alignment station. The die is then aligned to the heated bonding tool and picked up.
A dual tool bond head is available, which includes a heated pick-up tool and preform tool. Linear scrub with programmable amplitude and frequency can be mounted to the bond head. A four-sided collet is available for use with the linear scrub.
A rapid heat cycle workstage that securely holds the header (with clamping or vacuum pressure) and quickly ramps up to preform melting temperatures is available for both machines. The stage’s cover gas manifold dispenses heated gas at a set idle temperature. A cooling gas manifold option mounts on the stage’s heat shield and helps to solidify the bound.
A cube beam splitter viewing system gives a view of the header and diode for the alignment process. A video marker with a crosshair generator creates overlay images to mark the location of the emission point on the diode for centering to the header. A calibration scale allows for measuring in mils or inches. Ten separate image overlays and calibrations can be stored in memory.
|Required Equipment:||The following equipment from Semiconductor Equipment Corporation is required to perform this application:|
|The following equipment from Semiconductor Equipment Corporation is optional to perform this application:|
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