Yaomin Lin

Laser welding induced alignment distortion in butterfly laser module packages: effect of welding sequence

Welding-induced-alignment-distortion (WIAD) is a serious issue in fiber-optic component attachment using laser welding, which can significantly affect the packaging yield. Elimination or minimization of WIAD is expected to be possible if the laser welding process and all relevant packaging parameters can be optimized. The effect of laser welding sequence on WIAD for butterfly laser diode packages is reported for the first time in this work. The results demonstrate that WIAD deduction can be as high as 96% if an appropriate welding sequence is employed.

Effect of welding sequence on welding-induced-alignment-distortion in packaging of butterfly laser diode modules: Simulation and experiment

Controlling welding-induced-alignment-distortion (WIAD) and maintaining coupling efficiency is obviously the most challenging issue in assembling of fiber-optic components using laser welding. WIAD is the dominant barrier to having high packaging yields. Previous investigation has revealed that the WIAD in butterfly laser diode module packaging could be mitigated by properly choosing weld process parameters such as welding sequence. In this paper, the effect of welding sequence on WIAD is studied numerically by finite-element method (FEM) with a more realistic physics based laser welding model and experimentally by welding prototype butterfly packages. Results from both methods are compared. It is shown that the influence of welding process parameters on WIAD is significant and WIAD control is possible if proper welding sequence is employed.

Reliability issues of low-cost overmolded flip-chip packages

A significant need exists for the determination of critical stress characteristics within the low-cost overmolded flip-chip (OM-FC) packages. A systematic stress analysis is reported to investigate the OM-FC package for the optimal design of package geometries, materials combinations during the attachment, and thermal testing processes. A parametric study is conducted seeking the best package performance during the identified most stringent process which causes the largest stress within the low-cost substrate. High-stress location is predicted by finite-element analysis, and it was found that mold compound (MC) curing is the most stringent process for the reliability of substrate; higher underfill fillet, thicker die, larger die size without causing edge effect, solder mask defined structure resulted in smaller stresses in substrate. MC with lower coefficient of thermal expansion is a preferable and compliant substance that is good for using as molding and underfill material

Effect of welding sequence on laser-welding-induced alignment distortion in butterfly laser diode module packages

In fiber-optic component attachment using laser welding, the welding-induced-alignment-distortion (WIAD) is an issue significantly affecting the packaging yield. Our previous investigation has shown that an elimination or minimization of WIAD is possible if the relevant laser welding process parameters such as welding sequence can be optimized. In this work, a more realistic physics based laser welding model is introduced and incorporated into our finite element analysis model by a few user subroutines, the effect of welding sequence on WIAD in a butterfly laser diode module package is evaluated. The result verifies the conclusion that the effect of laser welding sequence on WIAD for butterfly laser diode packages is significant and WIAD control can be achieved as appropriate welding sequence is employed.

A novel assembling technique for fiber collimator arrays using UV-curable adhesives

Packaging and assembly covers almost 80% of the overall cost of any fiber-optic devices. It is thus a demanding issue to lower the cost of fiber-optic alignment and attachment process. This work summarizes the results for the development of automated alignment and attachment processes for the packaging of 1/spl times/8 collimator arrays, which are critical for many photonic devices. The emphasis of this work is on the comparison of the use of three different UV-curing adhesives (Adhesives A, B, and C). It is concluded that regardless of curing shrinkage, a proper adhesive joint design can alleviate the optical loss effect of the relative fiber-lens displacement induced during curing and the subsequent cooling processes.

Welding induced alignment distortion in DIP LD packages: Effect of laser welding sequence

In pigtailing of a single mode fiber to a semiconductor laser for optical communication applications, the tolerance for displacement of the fiber relative to the laser is extremely tight, a submicron movement can often lead to a significant misalignment and thus the reduction in the power coupled into the fiber. Among various fiber pigtailing assembly technologies, pulsed laser welding is the method with submicron accuracy and is most conducive to automation. However, the melting-solidification process during laser welding can often distort the pre-achieved fiber-optic alignment. This Welding-Induced-Alignment-Distortion (WIAD) is a serious concern and significantly affects the yield for single mode fiber pigtailing to a semiconductor laser. This work presents a method for predicting WIAD as a function of various processing, laser, tooling and materials parameters. More specifically, the degree of WIAD produced by the laser welding in a dual-in-line laser diode package is predicted for the first time. An optimal welding sequence is obtained for minimizing WIAD.

Package design and materials selection optimization for overmolded flip chip packaging

In overmolded flip chip (OM-FC) packaging, interface delamination-particularly at the die/underfill interface-is often expected to be a main type of failure mode. In this paper, a systematic stress analysis is performed by means of numerical simulations for the optimal design of package geometries and materials combinations. The behavior of the interfacial stresses at the die/underfill and die/mold-compound (MC) during the molding process is investigated, followed by a parametric study to examine the effects of the package geometries and materials parameters including the underfill fillet size, die thickness, die size, die standoff height, solder mask design pattern, MC used as underfill material, MC properties, etc., on the interfacial stresses. The results demonstrate that a proper selection of these parameters can mitigate the interfacial stresses, and thus is important for the reliability of the low-cost OM-FC packages

Adhesive joint design for minimizing fiber alignment shift during UV curing

In fiber-optic device packaging using UV curable adhesive bonding, the curing process often causes fiber alignment shift-distortion of the already aligned fiber-optic setups, and thus reduce the assembly yield. A new method for the adhesive joint design for minimizing fiber alignment shift during adhesive curing is reported in this paper. It is demonstrated that for any adhesive, the bonding joint can be designed to alleviate the alignment shift, regardless of adhesives used. The approach provides guideline for high yield and low-cost assembly of fiber-optic devices using adhesive bonding

Adhesive joint design for high yield and low cost assembly of fiberoptic devices

Adhesives tend to be popular because they are versatile, fill gaps on uneven surfaces, join dissimilar substrates and offer flexible adjustment time. Cures can be achieved within seconds for UV curable adhesives.. However, the curing process and cooling process of the adhesive may cause large distortions of the already aligned fiberoptic components, and thus reduce the assembly coupling efficiency. A new methodology for the adhesive design joint for fiberoptic component attachment is reported. Effect of adhesive materials properties, adhesive joint parameters, and UV curing conditions on the relative displacement, i.e., misalignment of fiber and lens arrays, during the curing process is investigated by means of finite element method. The results indicate that for a given adhesive and curing condition, the adhesive joint can be controlled to alleviate the alignment distortion during curing and cooling. Regardless of the adhesive used, the optical loss induced by the adhesive attachment process is found to be within the tolerance. This new adhesive joint design approach can be used for high yield and low cost assembly of photonic devices using adhesive bonding.

Weld clip design for minimization of welding-induced-alignment-distortion in butterfly laser module packages

The welding-induced-alignment-distortion (WIAD) or post-weld-shift (PWS) is a serious issue in assembling of fiberoptic components using laser welding, which may significantly affect the packaging yield. Our previous investigations have revealed that an elimination or minimization of the WIAD in butterfly laser module packaging is possible if laser welding sequence and pulse shape of the welding lasers can be optimized. This work represents our further attempt in minimizing the WIAD by design of welding tools: the weld clip. By means of numerical simulations, the influence of seven different types of weld clip on the WIAD in the assembly of the butterfly laser module packages has been investigated. A realistic physics based laser-materials interaction model is employed and the model combines the spatal and temporal characteristics of the laser beam and the thermophysical properties of the material. The results show that the design of weld clip is important in packaging of the butterfly modules and the alignment distortion induced during the laser welding process can be controlled within the minimal range by proper design of weld clip and selection of process parameters such as the welding sequence.