Question about solder mask layers

[san2004]

Dear Frnds,
I am doing PCB Designing for last 2 years.Whevever we generated or verified gerbers in CAM350 we always saw that in solder mask layers solder mask should be only arnd the pads of components. Is this wrong that if for 0603 components instead of two square shapes for two pins we can give only one rectangular shape covering both the pins ? Will it result in shorting of two pins ?
Currently I am verifying one 6 layer board where I saw that for all discrete components they have given only one rectangular shape..similarly for LQFP package for complete one row of 12 pins we can see only one rectangular shape in solder mask layer in gerber viewer software.
I afraid will this result in shorting of all pins ???
Pls help me regarding this ..
Thanks in advance..
Byeee

 

[Anonymous_Ricky]

SOLDER MASK DOUBT

Hi,
the above mentioned process is absolutely ok and will not result in any shorting of pads.
solder masking is used only to provide the masking of etched copper from solders the packages you have mentioned are so small that even if you provide the individual masking for each rather than complete rectangular box it will be so thin that it is absolutely negligible so if a rectangle is provided instead of masking for each pad it is OK.

regards,

Ricky

 

[FvM]

Re: SOLDER MASK DOUBT

Having converging pads in solder mask for rather big parts as 0603 sounds strange to my opinion. It must no necessarily bring on solder shorts, but I would doubt if the used technology parameters and/or padstacks are appropriate.

Most PCB technolgy parameters use enlarged mask pads or not-solder-mask defined (NSMD) footprints. Usual mask to copper spacing is 50 to 100 µm (2 to 4 mil). 50 u is for ultra fine-line (structures of 100 um or below). The mask pad enlargement ist usually achieved in post process, so in the pad stack mask pads are identical to copper pads.

There is a minimal structure size that can be reproduced reliable in solder masks structuring. Particularly small bridges between rectangular pads are in danger of breaking away and worst case deposit on top of component pads, hindering reflow solder. If this minimal width can't be kept, e. g. with 0.5 or 0.4 mm TSSOP pin spacing, the mask pads may be enlarged in padstack to force converging. A minimal mask structure width of 100 um can be expected with today's fine line technologies to my opinion.

0603 has typically 800 um (30 mils) square pads and 700 um pad to pad spacing in reflow footprint. It has enough room for a standard wire passing through. Then the huge solder mask pads could be a serious issue.

 

[san2004]

Re: SOLDER MASK DOUBT

Thanks a lot !!!!!
Its nice to see that still there are some ppl who share knowledge & help others....
Thanks !!