Masks for Bumping and Wafer Level Packaging
Over the past 20 years, we have developed a database of test patterns and combined them in a mask set. The purpose of the masks is to provide economical and versatile photolitho tools, particularly useful for process development, process validation, or final reliability qualification of a bumping product line.
The masks establish a rapid and thorough way of investigating the boundaries of processes. Our patterns are applicable, regardless of the fabrication process or material you intend to use. They are effective with any dielectric polymer suitable for wafer passivation.
Developing photolitho test mask sets from scratch is a costly venture. The first step is to determine which parameters need to be monitored during process development. Next, a test strategy needs to be established to monitor the parts during fabrication, as well as during reliability testing. Finally, suitable patterns must be defined, converted to a physical layout and documented before any fabrication can start.
We can short-circuit this process, save you many design iterations, and provide you with a roadmap for development. You can also use the masks to check and assess the capabilities of vendors. They are as useful to a polymer user than they are to a semiconductor house in need of evaluating the quality of bumping from packaging houses.
Matching PCB for reliability testing
Final reliability testing involves mounting WLP flip-chips on printed circuit boards for temperature cycling, humidity tests etc. The PCB must supply suitable connections to test the parts under bias. Accessibility to test points on the PCB must be provided to pinpoint the failure modes and their location. Finally, the PCB must be fabricated.
Although PCB fabrication does not require breakthrough design capabilities, it needs time and energy which can be better spent doing actual process development. We provide an efficient mean to speed the completion of your accelerated aging tests, saving you time and money.
Wafer-Bumping can supply you with a GDSII format database or with ready to use chrome masks sets specific to your mask aligning equipment. A variety of mask materials and polarity can be specified to meet your requirements.
With proximity aligners, chrome masks are essential to do bumping at the back-end. Masks fabricated on chrome blanks have the advantages of fine resolution, edge acuity and long shelf-life. Chrome is preferable to alternative materials that are opaque to ultra-violet light. Iron-oxide masks has the convenience of being semi-transparent in the visible spectrum, facilitating, in some cases, the alignment of dark field masks. Unfortunately, iron oxide masks are fragile, prone to pinholes, and worse, they degrade with use. Often without the knowledge of the mask aligner operator, they eventually leak UV through the supposedly high contrast (opaque) areas with disastrous consequences on process control. Although their price is higher, chrome masks remain the foundation of the industry .
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