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Recent Ask the Experts Questions
March 31, 2020
QFN Open Solder Joints
We are experiencing opens on assembled QFN components at a rate of approx 9%. This component has 2 rows of pads and the failure only appears in rows near the component center.
See the yellow area in the photo. Usually only 1 or 2 pads have opens. Our boards are double side reflow and this component is mounted on the first side. What is happening?
March 30, 2020
How to Eliminate Via Pits
Is there a process or solder paste designed for filling vias that will not cure with a pit in the via material? The pit may require rework.
We have tried several brands of paste and it runs out of the holes causing incomplete fill or in general the paste shrinks when cured. The hole sizes range from 0.005" to 0.025".
March 27, 2020
Bottom Terminated Components and Vias
Should the thermal vias of bottom terminated components be tented on both sides to prevent flux trapping and solder wicking, or is it sufficient to tent on the top side only? Or, should the vias just be plugged?
March 26, 2020
Floor Life of MSD Parts
We run small jobs so a reel of MSD components could be opened and closed a number of times. Each time we put a new desiccant pack and new humidity indicator card in the MSD bag and seal it.
If we total all the times we opened the bag it may exceeds 168 hours. Example: 8 hrs open then sealed for one or more days before we open the bag again for 10 hrs then sealed etc. If the humidity indicator card is not pink, do we still need to bake the components?
March 25, 2020
Components Jumping Around During Reflow
We reflowed a set of boards using a lead-free solder process and had issues with components jumping around from their initial placed position.
We then changed the process to leaded solder and had no problems. What could be causing the problem with lead-free?
March 24, 2020
Partially Visible or Hidden Solder Connections
This issue relates to IPC J-STD-001 section 4.18.3 - Partially Visible or Hidden Solder Connections.
The issue primarily arises out of the 75% barrel fill clause in IPC-A-610 - in which the QE group believes that, if the only view you have from a manual inspection standpoint is not of a top-down view, you have to assume the part is good.
The photo shows a component on a PCBA that we build and inspect. The QE is arguing that the angle of view is inadequate to make a quality call that the barrel fill is not sufficient. I don't feel that this is how this portion of the standard is to be read.
Being a CM, it is not necessarily feasible to add an X-Ray inspection to the process due to added cost. I would like to know how others in the industry work around situations like this?
March 23, 2020
IPC-A-610 Solder Joint Acceptability Question
Per IPC-A-610, figure 5-1, solder connection angle shall not exceed 90 degrees unless there is solder mask on the pad, or you are soldering to a high voltage application. This is the only place this is mentioned. Where other defects are called out according to Class; Acceptable, Process Indicator or Defect, this condition is not.
Per IPC-A-610 18.104.22.168, conditions that are not specified as defective or process indicators may be considered acceptable.
I recently had an operator question me on this. I feel that since this issue is not clearly call itout as a defect, it is acceptable. Our team looked at the verbiage above figure 5-1, and said that since it says we shall not have greater than 90 degree wetting, we need to rework the joint.
Would you please clarify this issue.
March 20, 2020
BGA BAll Sheer Testing
We soldered a lead-free 548-ball BGA. Afterreflow, we mechanically pulled the BGA component off the circuit board surface.See the areas of separation.
In some areas the pad was ripped off the circuit board surface and remained attached to the BGA ball. In other areas the joint sheered at the ball/pad interface.
What should we expect to see? Should all the joints act the same way? Is one attachment result better than the other?
March 19, 2020
Delamination Causing Scrap
We have been experiencing delamination on our printed board assemblies causing scrap.
Is there a way to definitively determine that the delamination is being caused by moisture vs. some other type of defect?
Is it possible to repair delamination in printed board assemblies?