6
\$\begingroup\$

What is the increase of a two-terminal component's height after it has been soldered to a PCB in comparison to its height in an unsoldered state? Any rules of thumb?

I am interested in both reflow and hand soldering.

To understand what the question is look at the picture below:

enter image description here
picture source

There is some extra height added to the component's height relative to the PCB's surface due to solder under the component.

My current understanding is that during reflow soldering nearly all solder fillet is extruded from beneath the component (to the so-called areas of toe, heel and sides), video link. However, there are several hundreds (or maybe tens) microns of solder left beneath the component. If hand soldered, the increase could be greater than if reflow soldered, I guess (due to a greater amount of solder left under the component).

I am going to put several bypass capacitors beneath a chip socket (there are several areas where components lower than 0.5 mm or 1.1 mm are allowed). Thus, I need to be precise.

\$\endgroup\$
15
  • 1
    \$\begingroup\$ It's going to depend on a lot of factors, including pad size, stencil thickness, type of solder paste, etc. I don't think there is a good way to estimate it accurately. \$\endgroup\$
    – DerStrom8
    Feb 26, 2017 at 14:52
  • \$\begingroup\$ @DerStrom8 10x. I guess/hope, adding 0.2 mm safety margin to a component's maximum nominal height (including manufacturing tolerance) should be enough. \$\endgroup\$
    – Sergei Gorbikov
    Feb 26, 2017 at 14:59
  • \$\begingroup\$ Laser cut 0.13mm stencil thickness is common, hand soldering is uncontrolled \$\endgroup\$
    – Tony Stewart EE75
    Feb 26, 2017 at 15:03
  • \$\begingroup\$ @TonyStewart.EEsince'75 10x, pal. \$\endgroup\$
    – Sergei Gorbikov
    Feb 26, 2017 at 15:05
  • \$\begingroup\$ 603 caps may be (0.76±0.25mm) \$\endgroup\$
    – Tony Stewart EE75
    Feb 26, 2017 at 15:07

1 Answer 1

Reset to default
6
\$\begingroup\$

I contacted my foundry (over e-mail and phone).

They said:

1) They use stencils of four heights: 80 um, 100 um, 127 um and 150 um. Standard (typical) stencil is of 127 um height.

2) Height of solder paste after application of a stencil (before heating) cannot be greater than height of stencil.

My comment: I don't remember for sure, but I think they meant, that average height of solder paste is equal (not just not greater) to height of stencil.

3) After heating (reflow) component descends.

So, I conclude:

The height of component after reflow soldering is smaller than nominal (datasheet) component's height plus height of stencil. Or, in other words, the ceiling value for component's height after reflow soldering is component's nominal height before soldering + stencil height.

PS1: I looked at several hand soldered capacitors. I do agree (with comments to the question) that the increase in case of hand soldering is uncontrollable. The additional height due to relatively large solder fillets under and above capacitors was as much as 0.5-0.6 mm (measured with eye).

PS2: Unfortunately, I don't have any reliable estimates how much the component descends after heating.

PS3: As soon as the PCB is produced and components are reflow mounted, I plan to update here about the resulting height and the socket.

\$\endgroup\$
1
  • \$\begingroup\$ I know this was four years ago, but did you ever take measurements of the remaining solder thickness after reflow? I have a similar situation now and any data you have would be really useful. Thanks! \$\endgroup\$
    – echo
    Apr 25, 2021 at 20:54

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.