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Connecting top and bottom SMD component pads using via

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3

$begingroup$

I am working on a 2 layer board and the PCB will be a double sided job. Some components on the top layer will have exact mirrors on the bottom right under them. My question is, for SMD components, can I just connect those pads with a via right in the center of the pads?

Does this affect electrical performance or production/assembly in any shape or form?

The reason: The bottom layer is a copper pour for ground and I have pads that belong to GND net so why not?

Please see the picture below (for demonstration porpuses I have moved the top component a little bit higher).

P.S. The components are TVS diodes (SM8J36CA). But my qustion is more general and is about wherever the pad size allows hosting a via in its center!

pcb pcb-design analog pcb-fabrication pcb-assembly

share|improve this question

edited 2 hours ago

JRE

22.2k43771

asked 3 hours ago

Sean87Sean87

1,543123360

$endgroup$

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  Talk to whoever is doing your assembly. Vias-in-pads generally wick solder away from the joint, causing reliability issues.
  $endgroup$
  – Dave Tweed♦
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  I wouldn't try it due to issues that can arise. They do this on BGAs where space is at a premium and it's called "via-in-pad" but they take special measures to make sure it works.
  $endgroup$
  – Toor
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  It's possible, but not recommended. If you're hand-assembling them, it should be okay, if a little harder to keep together. If this is for automated assembly, don't do it unless you really have no other option.
  $endgroup$
  – Hearth
  3 hours ago
  

  
  
  
  

add a comment | 

3

$begingroup$

I am working on a 2 layer board and the PCB will be a double sided job. Some components on the top layer will have exact mirrors on the bottom right under them. My question is, for SMD components, can I just connect those pads with a via right in the center of the pads?

Does this affect electrical performance or production/assembly in any shape or form?

The reason: The bottom layer is a copper pour for ground and I have pads that belong to GND net so why not?

Please see the picture below (for demonstration porpuses I have moved the top component a little bit higher).

P.S. The components are TVS diodes (SM8J36CA). But my qustion is more general and is about wherever the pad size allows hosting a via in its center!

pcb pcb-design analog pcb-fabrication pcb-assembly

share|improve this question

edited 2 hours ago

JRE

22.2k43771

asked 3 hours ago

Sean87Sean87

1,543123360

$endgroup$

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  Talk to whoever is doing your assembly. Vias-in-pads generally wick solder away from the joint, causing reliability issues.
  $endgroup$
  – Dave Tweed♦
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  I wouldn't try it due to issues that can arise. They do this on BGAs where space is at a premium and it's called "via-in-pad" but they take special measures to make sure it works.
  $endgroup$
  – Toor
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  It's possible, but not recommended. If you're hand-assembling them, it should be okay, if a little harder to keep together. If this is for automated assembly, don't do it unless you really have no other option.
  $endgroup$
  – Hearth
  3 hours ago
  

  
  
  
  

add a comment | 

$begingroup$

I am working on a 2 layer board and the PCB will be a double sided job. Some components on the top layer will have exact mirrors on the bottom right under them. My question is, for SMD components, can I just connect those pads with a via right in the center of the pads?

Does this affect electrical performance or production/assembly in any shape or form?

The reason: The bottom layer is a copper pour for ground and I have pads that belong to GND net so why not?

Please see the picture below (for demonstration porpuses I have moved the top component a little bit higher).

P.S. The components are TVS diodes (SM8J36CA). But my qustion is more general and is about wherever the pad size allows hosting a via in its center!

pcb pcb-design analog pcb-fabrication pcb-assembly

share|improve this question

edited 2 hours ago

JRE

22.2k43771

asked 3 hours ago

Sean87Sean87

1,543123360

$endgroup$

share|improve this question

edited 2 hours ago

JRE

22.2k43771

asked 3 hours ago

Sean87Sean87

1,543123360

share|improve this question

edited 2 hours ago

JRE

22.2k43771

asked 3 hours ago

Sean87Sean87

1,543123360

edited 2 hours ago

JRE

22.2k43771

edited 2 hours ago

JRE

22.2k43771

asked 3 hours ago

Sean87Sean87

1,543123360

asked 3 hours ago

Sean87Sean87

1,543123360

1 Answer
1

active

oldest

votes

4

$begingroup$

I am working on a 2 layer board and the PCB will be a double sided
job. Some components on the top layer will have exact mirrors on the
bottom right under them. My question is, for SMD components, can I
just connect those pads with a VIA right in the center of the pads?

Yes, will the assembly house be happy about it? No. Vias wick solder through them, plus using a stencil will apply the wrong amount of solder for the component because most of it will be in the hole.

If you do this, let the assembly house know (or if your hand soldering them who cares?) They will probably need to hand solder this component.

Does this affect electrical performance or production/assembly in any
shape or form?

If the signals in question aren't running at the +50Mhz speed then no, a few nH of inductance isn't going to make a difference. Vias might slow down very fast ESD events, if this is the only inductor in the current path which is unlikely. if adding a 10's of nH to the design makes a difference then run a PCB via inductance calculator and parallel the vias or do something else.

share|improve this answer

answered 2 hours ago

laptop2dlaptop2d

26.3k123381

$endgroup$

add a comment | 

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4

$begingroup$

I am working on a 2 layer board and the PCB will be a double sided
job. Some components on the top layer will have exact mirrors on the
bottom right under them. My question is, for SMD components, can I
just connect those pads with a VIA right in the center of the pads?

Yes, will the assembly house be happy about it? No. Vias wick solder through them, plus using a stencil will apply the wrong amount of solder for the component because most of it will be in the hole.

If you do this, let the assembly house know (or if your hand soldering them who cares?) They will probably need to hand solder this component.

Does this affect electrical performance or production/assembly in any
shape or form?

If the signals in question aren't running at the +50Mhz speed then no, a few nH of inductance isn't going to make a difference. Vias might slow down very fast ESD events, if this is the only inductor in the current path which is unlikely. if adding a 10's of nH to the design makes a difference then run a PCB via inductance calculator and parallel the vias or do something else.

share|improve this answer

answered 2 hours ago

laptop2dlaptop2d

26.3k123381

$endgroup$

add a comment | 

4

$begingroup$

I am working on a 2 layer board and the PCB will be a double sided
job. Some components on the top layer will have exact mirrors on the
bottom right under them. My question is, for SMD components, can I
just connect those pads with a VIA right in the center of the pads?

Yes, will the assembly house be happy about it? No. Vias wick solder through them, plus using a stencil will apply the wrong amount of solder for the component because most of it will be in the hole.

If you do this, let the assembly house know (or if your hand soldering them who cares?) They will probably need to hand solder this component.

Does this affect electrical performance or production/assembly in any
shape or form?

If the signals in question aren't running at the +50Mhz speed then no, a few nH of inductance isn't going to make a difference. Vias might slow down very fast ESD events, if this is the only inductor in the current path which is unlikely. if adding a 10's of nH to the design makes a difference then run a PCB via inductance calculator and parallel the vias or do something else.

share|improve this answer

answered 2 hours ago

laptop2dlaptop2d

26.3k123381

$endgroup$

add a comment | 

$begingroup$

I am working on a 2 layer board and the PCB will be a double sided
job. Some components on the top layer will have exact mirrors on the
bottom right under them. My question is, for SMD components, can I
just connect those pads with a VIA right in the center of the pads?

Yes, will the assembly house be happy about it? No. Vias wick solder through them, plus using a stencil will apply the wrong amount of solder for the component because most of it will be in the hole.

If you do this, let the assembly house know (or if your hand soldering them who cares?) They will probably need to hand solder this component.

Does this affect electrical performance or production/assembly in any
shape or form?

If the signals in question aren't running at the +50Mhz speed then no, a few nH of inductance isn't going to make a difference. Vias might slow down very fast ESD events, if this is the only inductor in the current path which is unlikely. if adding a 10's of nH to the design makes a difference then run a PCB via inductance calculator and parallel the vias or do something else.

share|improve this answer

answered 2 hours ago

laptop2dlaptop2d

26.3k123381

$endgroup$

share|improve this answer

answered 2 hours ago

laptop2dlaptop2d

26.3k123381

answered 2 hours ago

laptop2dlaptop2d

26.3k123381

answered 2 hours ago

laptop2dlaptop2d

26.3k123381