Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Solder under bottomside SMT components

John Silvestri

#15260

Solder under bottomside SMT components | 24 June, 1998

Has anyone seen a problem with solder under chip components, in-between the glue and the component or in-between the mask and the component? We seen both. What could be causing this? This has only been detected on one of our products. All the rest which use the same materials and profiles seem to be good.

John

reply »

Phillip Hunter

#15262

Re: Solder under bottomside SMT components | 24 June, 1998

| Has anyone seen a problem with solder under chip components, in-between the glue and the component or in-between the mask and the component? We seen both. | What could be causing this? This has only been detected on one of our products. All the rest which use the same materials and profiles seem to be good. | | John | I must assume that the chips are glued to the PCB, cured, then wave soldered. If you are seeing solder shorts under the chips this is probably an indication of outgassing. Epoxy is hydroscopic-that is it readily ablorbs moisture from the atmosphere. The moisture expands forming steam in your curing oven. The steam evaporates, leaving chambers or cavities to which liquid solder easily enters. Typically this problem occures when stencil printing epoxy. Here is a simple test for all epoxies. Dispense epoxy in between two glass slides. Sandwich them together and cure in your oven. If moisture is present you will EASILY see the cavities made from the steam. Heraus makes some anti-hydroscopic epoxies (PD44). Also, check your cure schedule. It is helpful to stay below the boiling point of water and slowly evaporate the water rather than vaporize it instantly. This may slow your line down if your oven is a multi-zone linear type. Phillip Hunter Laughlin-Wilt Group Inc. 503-672-4388

reply »

Bob Willis

#15261

Re: Solder under bottomside SMT components | 10 July, 1998

Yes this can be a killer. Its caused by glues with a high water content or fast curing of glues. When you get solder going through the glue it is litterally sucked in during solder wave contact. If you have never seen it you would never believe it but I have examined the problem for a number of customers. The defect type and examples are on my download evaluation CD ROM "Bob Willis SMT Defect Guide" try it out on http://www.bobwillis.co.uk A glue manufacturer starting with H had the problem first but others have also seen the problem. If the glue is not in the glue it probably an Omega Wave !!!! | Has anyone seen a problem with solder under chip components, in-between the glue and the component or in-between the mask and the component? We seen both. | What could be causing this? This has only been detected on one of our products. All the rest which use the same materials and profiles seem to be good. | | John |

reply »

 Reflow System

Rework Training Materials