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Recent Ask the Experts Questions
July 17, 2019
Suggested Limit for PCBA Heat Cycles
What is the suggested limit for the total number heating cycles that can be done on one PCB assembly? Our PCBs contain BGAs, leadless components and large fine pitch components.
July 16, 2019
Test Probe Problems After Pin-In-Paste
We are having test probe contact issues with our Pin-In-Paste process. The root cause being the flux residue on the surface of the solder joint. Test probes can't penetrate the residue which is soft & gummy following reflow and within a few days turns to hard and brittle.

Roughly a third of the solder joints lose some of the solder paste volume during reflow process (can be found in the first zone of the oven). However we still have adequate solder joints. In these cases the test probes can make a proper connection.

We have tried using different test probes but feel like we are taking care of the symptom and not the root cause itself. Should all the flux vaporize off in the reflow process? Any suggestions?
July 15, 2019
Blow Holes and Disturbed Joints
We are finding many blow holes and disturbed joints after reflow. Our PCB is 1.7 mm thick and baked prior to reflow at 120 C for 6 hours. The process is non RoHS. Peak temp for reflow is 220 C. What could be going wrong?
July 12, 2019
Adding Chlorine to a DI (Deionization) Water System
We have had a recent issue of bacteria accumulation in our DI (Deionization) reservoir. In order to combat this we have put in a floater (similar to one found in swimming pools) containing chlorine tablets. Is this dangerous to use in our system? What limit should the chlorine levels be in the DI reservoir?
July 11, 2019
Solder Mask Ghosting
Some here are convinced that we have solder mask ghosting on PCBs because our global suppliers are not curing the mask sufficiently. The problem is that our PCB's come from many major suppliers in Taiwan and ASIA, over several different suppliers and board types.

I do not buy the notion the entire world chooses to not cure the mask. Any suggestions on how to get more data on the ghosting issue where multiple suppliers are involved?
July 10, 2019
How Do You Calculate Solder Paste Volume?
I have a connector with 6 rectangular mounting tabs. The tabs are 1.5 mm x 0.6 mm.

How can I calculate the recommended volume of solder paste for these mounting tabs?
July 9, 2019
Solder Balling Splash After Reflow
A lot of balls are observed after reflow process along and under SMD components. (see images)We have not found the root cause, any ideas are welcome.

  • PCB finish surface: HAL
  • Solder Paste: SN62MP100AGS90
  • Reflow oven: Vapor Phase with Galden
  • Problem seen with one specific PCB supplier but not with another one
  • Rebaking the pcb before process do not solve the problem

July 8, 2019
Reflow Profile for Mixed Lead-Free and Leaded
What changes are required for using tin/lead paste on lead-free circuit boards? Does the oven profile have to be adjusted for lead-free boards, or does the tin/lead solder paste determine the oven profile?
July 3, 2019
IPC SOIC Defect Question
If solder touches the body of a ceramic or metal component it is classified as a defect, but NOT if it is a plastic body SOIC. Why is there a difference?

Reference: IPC-A-610, section Flat Gull Wing Leads
July 2, 2019
Burned Chip Repair
I have a circuit board with a burned chip. The manufacturer wants to charge an arm and a leg for a new board. Can this type or repair be done reliably? Where can I turn for guidance? Do you know anyone I can send this board to and have it done professionally?