Issue link: https://iconnect007.uberflip.com/i/1441485
72 DESIGN007 MAGAZINE I JANUARY 2022 Shaughnessy: From our surveys, we've learned that laminates are a problem. ey can't trust the datasheets, they don't understand the properties, or both. Amla: Right now, people are trying to model materials. ey want to do this work up front and they need some information. ey want to find out properties like the shear modulus of the material, the CTE, in X, Y and Z, whereas the datasheets just publish one data point. e issue is that there has to be a computational engine that can help predict the properties for a multitude of configurations. What is needed in the industry is an engine that can help you run these simulations and get a whole gamut of properties out—solder joint reliability, CTE, Z-axis expansion, etc.—because what you have now is a single point estimate in datasheets, and there's no way that the supplier can do that much testing to include all possible data requirements. For example, now you're building this board. e datasheet says the CTE is 40 ppm/°C. You say, "I'm going to use this material." en you use 1078, 78% for that construction, and lo and behold, you find out your CTEs are 85. en you ask, "What happened?" e conclusion is that you can't trust the data because you took that one data point, and you started treating the laminate as silicon or any other isotropic homogenous material. Silicon is silicon, with a 2.6 ppm/°C CTE, and it does not change with different configurations—but that doesn't happen with composites; every composite structure will behave as a function of its parts. at's the basic misunderstanding that leads to a lot of confusion and finger pointing, because people don't understand that these are com- posites. ese composites have glass, which is almost 20 times stiffer than the resin and prop- erties of the composite lie somewhere in the middle, which can't be eyeballed and needs to be computed. en there's a glass transition, so all those properties come into play. So, the confusion is mainly because most people only understand bits and pieces of the problem. Barry Matties: One of the things that we hear, Tarun, is that the performance specifications of a material are optimal, but real world is differ- ent than what they might get in laboratories. It sounds like that's what you're describing here. Amla: No, in the performance specifications, the information is given, but now you're just putting it together. You're making a board and you want to have certain dielectric spacing. What happens is that gives you rise to the over- all board properties, so this is the discussion I've been having with some people who asked for low CTE laminates in X and Y, and one of their vendors developed such a material. But then when they built the boards, they said the board CTE didn't change much. It was still about 18.5 in X and Y, and the whole idea was to reduce the CTE of the board to improve the solder joint reliability. But designers failed to realize that if you've got a lot of copper in the board, then it will dominate because it is a lot stronger and stiffer than the dielectric, and by changing the properties of the dielectric, the effect may still not be enough to reduce the CTE. So, that understanding of the physics of when you put all these things together is not there. So, it's not that the laminate guys are not giv- ing you the information. ey're giving you the exact information you are asking for. But that does not mean that the laminate proper- ties will transport over to the board and hence Right now, people are trying to model materials. They want to do this work up front and they need some information.