FEMAP Model of Circuit Card Assy Help 1

[SolidworksFan]

Has anyone used FEMAP to analyze a circuit card assembly with its components? I am trying to determine the change in the natural frequency of a loaded PWB.

PRO/E (boo hiss) will be used to generate the geometry. Once imported into FEMAP, I changed the PWB to a midsurface (ie shell elements).

The question is how to model (in FEMAP) the small components? The legs of a chip can be quite tiny (less than .026" wide or smaller). So the thickness is even smaller. The mesh size would need to be crazy small for the chip.

Any ideas?

 

[BlasMolero]

Hello!,
Small components like a chip will not stiff the PCB, then the correct meshing approach is to consider them ass MASS, simply put a mass element in the CoG of the chip and attach to OCB using RBE3 elements, this is the most practical & accurate way to model small componentes, OK?.

Best rgards,
Blas.

By the way, in FEMAP use command "Tools > Mass Properties > Solid Properties", then FEMAP will create for you the node & mass element at the CG of the chip.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[SolidworksFan]

Hello Blas:

Thanks for all of the advise. I really like that you are giving specific FEMAP instructions not just general.

Randy

 

[SolidworksFan]

Blas:
I agree that the small chips will not stiffen the board. Just for fun let's say I have a larger chip like a BGA that may add some stiffness. The manufactures give dimensional data but not chip material info. I have an old Solidworks FEA training manual that used Ceramic Porcelain for chip material in an example problem.

Does this seem like a resonable material? I no longer have access to the software so I do not know what properties to use.

Again, I am only playing "what if" games at this point. What material would you folks use to simulate a chip in FEMAP?

 

[BlasMolero]

Hello!,
In this case you can model the big chips as a solid volume and mesh using CHEXA elements. Also use GLUE contact surface-to-surface to attached both componentes. Glue is a simple and effective method to join meshes which are dissimilar. It correctly transfers displacement and loads resulting in an accurate strain and stress condition at the interface. The grid points on glued edges and surfaces do not need to be coincident.

Regarding material properties of Ceramic Porcelain, make a search at

http://www.matweb.com,

or better visit the TMG THERMAL Wizard at the following address:

http://www.thermal-wizard.com/

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48011 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[SolidworksFan]

Blas:

Do you need to model the chips as a separte "part" or can I simply extrude them out of the mid surface I created for the pcb? I have seen that you can assign different materials to the extruded chip.