search.noResults

search.searching

dataCollection.invalidEmail
note.createNoteMessage

search.noResults

search.searching

orderForm.title

orderForm.productCode
orderForm.description
orderForm.quantity
orderForm.itemPrice
orderForm.price
orderForm.totalPrice
orderForm.deliveryDetails.billingAddress
orderForm.deliveryDetails.deliveryAddress
orderForm.noItems
Page 36


www.us- tech.com


June, 2019


Challenges in Printed Circuit Board Acid Copper Plating


By Akber Roy, CEO, Rush PCB, Inc.


of this method of plating PCBs is the poor throwing power of the electrolyte. This results in excessive plating times for achieving mini- mum copper thickness in areas with low cur- rent density, while high current density areas get too much copper deposit. In a PCB with through holes, the high


U


current density areas are at traces and at the edges around the holes and the low cur- rent density areas are at midway to the length of the hole. This not only leads to wasted copper, but also adds to the cost. On the surface of the PCB, there can be


over-plating on isolated traces when com- pared to larger ground planes, since the for- mer are areas with high current density, while the latter are areas of low current density. Within the hole, the throwing power of the electrolyte sets the challenge in achieving the minimum copper thickness re- quired at the center. The challenge increases lin- early with an increase of the aspect ratio of the hole, decreasing as the throwing power of the elec- trolyte increases In acid copper plating, the challenge is to


sing direct current during acid copper plating has been a staple method for PCB manufac- turers. However, one of the basic drawbacks


fecting the throughput of PCBs drastically. Rush PCB adopts a two-pronged approach to reduce the overall plating time, and to achieve a uniform dis-


specific duration cyclically, creating current flow in a square pulse waveform. Although the current flow is not a constant, the pulse plating technique may cause the plating current density in the on-pulse to increase to more than ten times what is achieved during regular DC current plat- ing. This high current density reduces the excessive potential of the metal ions, mak- ing the deposit a layer of fine grains. This leads to a more uniform deposition of cop- per as a detailed crystalline coating. The ratio between the on-time to the


Rush PCB uses pulse plating and reverse pulse plating to apply uniform copper coatings and thicknesses.


tribution of copper deposit. These two steps are as follows: using pulse plat-


ing and reverse pulse plating techniques rather than traditional direct current for acid plating; and using organic additives during acid copper plating.


achieve proper thickness distribution and surface uniformity without unduly compromising metal- lurgical properties, such as percent elongation and tensile strength of the deposit. Sometimes it is dif- ficult to achieve surface uniformity, because of the formation of nodules. Reducing the current density can equalize the


copper thickness to some extent, but leads to an in- ordinate increase in the overall plating time, af-


Pulse Plating Technique Rush PCB uses the technique of pulse plating


to control the electrodeposition of copper rather than a constant supply of current. Pulse plating relies on the time function to start and stop the current sup- ply, thus improving the physical and chemical prop- erties of the plating film. By modulating the current supply, the technique switches the current off for a


cycle time of the pulse train is its duty cycle. Therefore, a duty cycle of 100 percent essen- tially produces a continuous current as in the traditional DC current plating. The pulse plating technique uses a duty cycle al- ways below 100 percent, the actual value de- pending upon the characteristics of the PCB undergoing the plating. While for most PCB plating applica- tions the pulse plating technique is ade-


quate, more complex PCBs require an enhanced version of pulse plating. Rush PCB uses a reverse pulse plating technique in such cases. This im- proved technique uses an additional pulse in the cycle, with an opposing polarity. Therefore, each current cycle now consists of a forward pulse, a re- verse pulse, and an off period. The time period and amplitudes of the two pulses are individually ad- justable and an electronic circuit controls them. In most cases, a computer generates the necessary waveform. For proper plating thickness and uniformity, Rush uses an amplitude of the reverse pulse that


Continued on next page


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92