Difference betwen pad layer and top layer in cadsoft eagle

Hey
I want to know the difference between the pad layer and top layer in eagle. Actually i created some libraries from scratch and used smd option and i thought that red colour rectangles are called pad(which i think i am right) but as i see different layers on my board layout while using the component they are placed on top layer. I understand they are the copper markings that will be printed on top layer but what does pad layer actually has?????
thanks in advance

their is a through hole pad and smd pades. smd pades are two types top and bottom. through hole is applicable in all layers

A pad usually shows up in green with the default colour scheme and is the soldering area for a through hole component. An SMD has different attributes. While it looks the same colour as the copper layer you also automatically get a solder paste layer which you don't get with a pad. Both a pad and SMD will have solder resist layers automatically added.

Keith

keith1200rs said:

A pad usually shows up in green with the default colour scheme and is the soldering area for a through hole component

Click to expand...

1. this means in through hole component its just the area where molten solder will fall and it comes in pad layer??? right

keith1200rs said:

While it looks the same colour as the copper layer you also automatically get a solder paste layer which you don't get with a pad

Click to expand...

2. Smd as i get are surface mount component so no drilling is required hence in this case we just mount the component on the board area where copper SMD pad was printed hence connection is made. And all these smd pads are therefore on top layer ofcourse am i right???

The main difference is solder resist and solder paste.

1. yes, solder will be on the pad area. It is the same as copper but not covered in solder resist (look at layer 29 to see the difference between a pad and normal copper).

2. yes, the SMD is the area that soldering is done. Again, no solder resist but also a solder paste mask (look at layers 29 and 31 to see the difference between a pad and SMD [as well as not having a hole on SMD]).

Keith

keith1200rs said:

The main difference is solder resist and solder paste.

1. yes, solder will be on the pad area. It is the same as copper but not covered in solder resist (look at layer 29 to see the difference between a pad and normal copper).

Click to expand...

1.I think i got it now layer 29 tstop is solder resist basically here solder resist layer WILL NOT FLOW ie the green colour epoxy i think?As soon as i activate tstop it gave a covering over pad so thats kind of protecting pad right? copper tracksk however dont show any such covering so they will be covered in solder resist right?

keith1200rs said:

2. yes, the SMD is the area that soldering is done. Again, no solder resist but also a solder paste mask (look at layers 29 and 31 to see the difference between a pad and SMD [as well as not having a hole on SMD]).

Click to expand...

2.IN SMD i have additional covering on as i activate layer 31 that is solder paste right? whats its use?

Solder resist is a negative layer - in other words you get solder resist everywhere EXCEPT where there is something drawn on the solder resist layer. It prevents solder ending up where you don't want it and also helps prevent solder bridging with close pads/SMDs. You can also specify it to be slightly larger or smaller than the pads if required.

The solder paste layer is for soldering SMDs. A laser cut stencil is made from that layer and solder paste (or "cream" as Eagle calls it) is screen printed onto the PCB. The SMD components are placed on the PCB onto the solder paste and then the PCB goes through a reflow oven to solder it.

The will be some tutorial/descriptions of the PCB manufacturing/assembly process on the internet which may help.

Keith

hey thanks a ton
even i found some good docs regarding diiferent layers and eagle online.
again thanks a ton.I really appreciate your help
Aashish