Hi,
I just talking with my contact at our PCB assembly house, and he said they had difficulty getting the solder paste to flow thru the tiny holes in the screen for this part. I looked on the product page and also at the data sheet for soldering recommendations, but I didn't see any.
Could someone point me to suggested assembly requirements? What solder paste, what temperature profile, what hole size for the screen?
Thanks,
Bob Kruse
Bob,
A .4mm pitch devices will require a stencil thickness of 4mils preferably in a high quality laser cut stencil. The opening of the aperture should be:
Board Layout
In making the pad size for the WCSP balls, it is recommended that the layout use nonsolder mask defined (NSMD) land. With this method, the solder mask opening is made larger than the desired land area, and the opening size is defined by the copper pad width. Figure 5 shows the appropriate diameters for a WCSP layout.
|
SOLDER
PAD |
COPPER |
COPPER
|
STENCIL
|
||
|
Nonsolder mask defined (NSMD) |
0.23 mm |
0.310 mm |
1 oz max (0.032 mm) |
0.275 mm x 0.275 mm
Sq. |
0.1 mm thick |
(1) Circuit traces from NSMD defined PWB lands should be 75 mm to 100 mm wide in the exposed area inside the solder mask opening. Wider trace widths reduce device stand off and impact reliability.
(2) Best reliability results are achieved when the PWB laminate glass transition temperature is above the operating the range of the intended application.
(3) Recommend solder paste is Type 3 or Type 4.
(4) For a PWB using a Ni/Au surface finish, the gold thickness should be less 0.5 mm to avoid a reduction in thermal fatigue performance.
(5) Solder mask thickness should be less than 20 mm on top of the copper circuit pattern
(6) Best solder stencil performance is achieved using laser cut stencils with electro polishing. Use of chemically etched stencils give inferior solder paste volume control.
(7) Trace routing away from WCSP device should be balanced in X & Y directions to avoid unintentional component movement due to solder wetting forces.
