Deep to Learn mSAP IC Substrate Technology
The never-ending demand for smaller, faster, and more powerful electronic devices has driven the semiconductor industry to innovate not only in chip design but also in packaging and interconnect technologies. The Integrated Circuit (IC) substrate, which is the electrical interface to and the mechanical support for the silicon die, has seen dramatic changes. Among the various processing schemes, Modified Semi-Additive Process (mSAP) is a breakthrough technology for making high density interconnect (HDI) substrates. This paper presents an in-depth analysis of the mSAP IC substrate technology including its manufacturing flow, process features as well as a direct comparison to other widely utilized patterning techniques. For companies building the next generation of electronics, working with a leading mSAP IC Substrate supplier is key to realizing the potential of advanced chip architectures.
The Evolution of IC Substrate Patterning
Functionally, the IC substrate serves to provide the routing from the very high density input/output pads of a semiconductor chip to the much lower density of a printed circuit board. With increasing chip input and output nums and decreasing pitches, the substrate needs to have finer lines and spaces to meet the requirement of dense routing. Conventional PCB manufacturing processes, such as subtractive etching, are challenged when defining features finer than 30 micrometers . This required the introduction of additive techniques, which is how SAP and eventually mSAP came to be. An mSAP IC Substrate manufacturer takes advantage of this process to provide a solution that lies between the traditional PCB offering and the high density requirements of today’s flip-chip and fan-out packages. To really know what mSAP is all about, you need to look at it relative to the prior and competing solutions.
The Subtractive, SAP and mSAP Process Compared
Three processes, Subtractive, SAP and mSAP, dominate the patterning of conductive lines on IC substrates. Each process has particular attributes, business implications, etc. subtraction processes has least environmental impact and mSAP is most wasteful and harmfull. Subtractive Process: This is the conventional technique for making PCBs. It is based on a laminate core clad on both sides with a very thick layer of copper foil. Photoresist is deposited and patterned, revealing copper to be removed. Then the substrate is etched and the email substrate is etched and extraneous copper is cleaved away. One major disadvantage of the subtractive process is undercutting. As copper is removed from the etchant in the vertical direction, it is also removed in the horizontal direction beneath the photoresist. This leads to line cross-sections that are trapezoidal which restricts how narrow and close lines and spaces can be. It is usually not applicable to fine-pitch IC substrates. SAP (Semi-Additive Process): SAP is basically an additive process processing a dielectric substrate that is devoid of copper cladding. A very thin seed layer of copper is deposited across the whole area, commonly through electroless plating. Photoresist is spun on and then patterned to open the areas where the circuitry is wanted. The copper is then electroplated in these open areas to the desired thickness. Finally the photoresist is removed and the thin seed layer is rapidly etched. SAP can produce extremely fine lines and spaces with almost vertical sidewalls but it is an involved and expensive process. mSAP (Modified Semi-Additive Process): shares mSAP is a semi subtractive/semi additive process. It begins with a laminate core with a thin layer of copper foil. This thin foil is the seed layer for subsequent plating. Like SAP, photoresist is spun on and patterned to create circuit traces. Next, copper is electro plated onto the exposed thin foil to form the needed thickness of the circuit. The photoresist is removed after plating. The essential final operation is the flash etch to remove the original thin copper foil in the unplated portions. Since the starting copper foil is thin, the undercutting in the flash etching is very little enabling much finer features compared with the subtractive process, and more cost effective and more suitable for the existing manufacturing system infrastructure than pure SAP. A mSAP Substrate manufacturer can confidently achieve line and space from 12 to 25 microns.
The mSAP IC Substrate Manufacturing Flow
The mSAP IC substrate production process is an elaborate, multi-stage process requiring rigorous environmental control and extremely high precision machines. A top mSAP Substrate supplier has a well-defined process flow to maintain yield and reliability. It starts with core preparation and drilling. The substrate material, normally a high-performance epoxy laminate with woven glass fiberglass, is drilled with holes to provide vertical electrical connections. After drilling the holes are processed to remove resin smear, and then electroless copper is deposited on the entire surface. Resist lamination and imaging follow. A dry film photoresist is laminated to the copper clad panel and exposed with high-resolution direct imaging technology. The panel is developed to open up the thin copper seed layer under where the circuitry was formed with the copper seed layer. Copper pattern electroplating thickens up the traces and fills the vias to the desired thickness. Then the resist is stripped and the thin seed layer is removed from the non-circuit areas by flash etching. This process step is what separates mSAP from subtractive etching and allows you to define fine-line patterns. The opportunity in solder mask application and surface finish, final inspection and testing.
Important Process Factors and Problems
The mSAP process lends itself to multiple advantages that have made it the preferred technology for high-density IC substrates. The main benefit is the possible resolution of fine line and space. Enhanced mSAP allows for line and space values as small as 15 micrometers with good dimensional control. The high density of routing is critical to support high input output counts from advanced chip packages. mSAP produces nearly rectangular cross-section and vertical sidewall conductor traces. This profile greatly enhances signal integrity, particularly at high frequency. By employing thin copper foils and high performance imaging techniques, an mSAP IC Substrate supplier can provide enhanced layer-to-layer registration, which is crucial for intricate multi-layer substrates. But mSAP is a major hurdle. It is a process demanding very high purity, otherwise the micro-particle contamination results in defects. Accurate management of plating uniformity, etching rate, and photoresist characteristics is important to maintain high yield. The best mSAP IC Substrate manufacturer has to take advanced technology as backbone to surmount these difficulties by means of process engineering and quality control.
Functions of the mSAP IC Substrate Manufacturer
Selection of the appropriate manufacturing partner is critical for firms employing mSAP technology. High-end mSAP IC Substrate manufacturer should have world-leading facilities such as high precision laser drillers, direct imaging systems, advanced plating lines etc, and at the same time advanced mSAP IC Substrate technology know-how and expertise in materials and process.
In addition, top mSAP IC Substrate manufacturer also provides design for manufacturability(DfM) support by working with customers in the early stages of design to finalize the substrate design that fit for the mSAP process. It is a co-optimization to get the highest yield, lowest cost and shortest time-to-market.
Conclusion
The mSAP IC substrate technology has given ratentation for growth in the semiconductor industry. Utilizing the advantages of additive plating and the convenience of thin copper foils, mSAP is a scalable and cost effective process for the production of high density interconnects (HDI) used in current and next generation electronics. For semiconductor companies and system designers, gaining a thorough understanding of the complexities of the mSAP process and working with a best-in-class mSAP IC Substrate manufacturer is critical to enabling product differentiation success in an ever more challenging electronics market.
