Lead To hole Ratios are fairly important but not normally a cause for Blow Holes.

If you are using Single Sided PCBs then many things are blamed on lead to hole ratios, when in fact the problem is incorrect drilling leaving a laminate burr inside the hole wall which then naturally de wets solder.

If the problem is with PTH boards then this can be caused by HASL fluids attracting moisture into the holes, sometimes baking works, but sometimes there is too much high boiling solvents left to bake out as they are there to withstands high temperature so stands to reason they cannot be baked out.

This can be tested for as if you leave an Iron tip for 4-5 seconds on the blown joint you will see an acrid smoke come off with the solder fizzing and popping and a black spec appear on the molten solder normally.

If it is only in a certain area of the PCB then it could more likely be thin plating so you get hole wall break out, get that area micro sectioned and wall plating including Copper thickness tested.

If the PCB is Silver Finish then this too can produce blow holes and the only thing that really helps is to flow the PCB twice, we believe there is resist sometimes improperly removed or leached/bled over the holes and by soldering it twice this actually removes the residue and gives an improved solder joint.

Would be helpful to know what solder finish PCB is and what type i.e. single or double sided.

Hope it helps

The blow holes are not really related to the ratio. The recommended hole diameter for laedfree is 0,3mm bigger then the component lead.

Most of the time the blow holes are related to the PCB. Since you tried different parameter and fluxers you may consider a different way.

I had good success with the same problem by running the process temperatures on the lower end. Specially the solder bath temperature as low as 260C and the contact time as short as possible. The preheat was just 100C.

If possible I would try to use a different PCB supplier.

Christian Ott Sales Manager, Seho Christian Ott knows electronic manufacturing companies around the world and their specific requirements. He has hands on experience with Selective, Reflow and Wave soldering processes.

Blow holes have many causes. One possible cause is air escaping from between the layer of the PCB through pin holes in the barrel of the plated through hole. This will happen no matter how much you pre-bake the board because it's air and not moisture being forced out as the board heats.

The only solution is to look to your board vendor to make sure the through-hole plating is 100% with no pin holes.

The IPC publishes manyquality and inspection documents for the electronics manufacturing industry. I think theIPC-2221A "Standard for Printed Board Design" will have the hole to lead ratio recommendation.

Paul Austen Senior Project Engineer, Electronic Controls Design Inc Paul Austen is a 30 year veteran Senior Project Engineer with ECD in Milwaukie, Oregon. Paul has seen and worked with the electronic manufacturing industry from many points of view, including: technician, designer, manufacture, and customer.

Many times this can be caused by humidity or any water on the PCB.

Todd O'Neil Sales Manager, Soldering products, JUKI Automation Sys. Mr. O'Neil has been part of the electronics manufacturing field for 17 years. As Sales Manager for all Soldering products at JUKI, his main objective is to continue to supply equipment providing the "Lowest Cost of Ownership."