Improve Laminate Quality With Fab Notes
Control Process, Elevate Standards via Latest Materials
Fab notes are a great tool to control the quality and performance of your PCBs. However, when written incorrectly, they can have quite the opposite effect. In this newsletter, we will be discussing the effects of laminate callouts.
With the onset of RoHS compliance, fabrication notes take on a higher level of importance. Previously, FR4 has been used as almost a generic term for material type. Typically, this has referred to 130Tg FR4 which is almost an all-purpose laminate. With lead-free assembly temperatures, there are more critical characteristics that must be addressed.
Common callouts for material often tend not to address these critical characteristics. Here are a few of the current callouts and the potential issues that may arise.
Callout: IS410 / 370HR
Potential Issue
Locking yourself into a laminate by brand name. This limits your supply base to those that use those particular laminates. Also, it limits your product to not taking advantage of new, improved materials that may come to market over time. Also, these are phenolic materials that have a host of issues, as addressed in our lead-free webinar and the "Tired of Delamination" section of this newsletter.
Callout: FR4
Potential Issue
Standard FR4 materials are not capable of surviving lead-free assembly on most designs.
Callout: RoHS Compliant
Potential Issue
This can include standard FR4 material. While standard FR4 is RoHS compliant, it is not necessarily lead-free capable.
Callout: 180�C Tg
Potential Issue
Tg does not guarantee adequate Td. Td, or Decomposition Temperature, is one of the most critical characteristics of a lead-free assembly capable material.
Callout: 340�C Td
Potential Issue
This high of a level of Td may prohibit the use of better performing materials that may save yield and cost.
Saturn Solution
We propose that fab notes be used to not only control the quality of material used on the product, but also to take advantage of new material and technology developments that will occur over time.
The best way to accomplish this is to refer to industry standard IPC 4101 material categories. There are currently 6 individual IPC categories for lead-free capable materials. Generally, they can be grouped to form 3 primary lead-free material categories.
We are asked for our suggestions quite frequently. While each design and operating requirements should be reviewed to 100% verification that a particular material category is appropriate, the following provides a good starting point.
If previous material was standard 130Tg FR-4: "Material should meet or exceed requirements of IPC 4101/101 or /121". Using this callout allows your supply base to take advantage of /101 or /121 materials as they are lower in cost. Also, if your supply base only uses /124 or /126 materials for example, they can still do so as those materials typically backwards qualify to the lower IPC 4101 categories.
If previous material was 170Tg FR4: "Material should meet or exceed requirements of IPC 4101/126 or 129 (or /99 or /124 if you can go down to 150Tg)".
If you view our lead-free cost reduction webinar, you will see lab test results showing the superior mechanical performance of /99 and /124 materials over /126 and /129 materials. In effect, the mid-grade materials are more robust than the higher grade materials. 
